I'm a GRM cliche. GMT400 content inside.

Ordered a MPFI conversion this morning. I priced the brake hydraulics refresh and it was surprisingly cheap, so its probably next, but I really need some tint for this thing, and Ive really been wanting to do exhaust. Nothing crazy, maybe a muffler back, but its a weird 2 in 1 out design and I want something that will also work once I do the full exhaust, and to not be obnoxiously loud, and quiet when cruising. Currently leaning towards an 18" magnaflow.

Any exhaust recommendations. Future plans are long tubes, catted X and a single exit in stock location or maybe a dual exit in stock location

I did the MPFI conversion today.

Got the plenum off. Wasnt a bad job, just a bunch of crap and brackets in the way.

I had no intentions of major modifications to this or deleting any emission components, but seeing all the nasty carbon build up really had me considering deleting the egr. With the plenum off I didnt see anything wrong with the old spider. no clean spots from fuel dripping or anything like that.

New Delco kit. Came with the plenum and throttle body gaskets

Got the MPFI unit in

Got her all back together

I also popped a check engine light on yesterday. It was a P0404. EGR code. So when it was all back together I hooked up the scanner and watched actual vs desired EGR position, and the EGR valve (which was installed last year) would work for a second then get stuck and quit responding. So I went ahead and put an EGR valve on it and cleaned the ports in the manifold.

Been chasing fuel trim issues, fuel pump helped but them did still seem to skew on the lean side. I knew the truck had a K&N and figured it was filthy like most of them. Thought Id clean it and the MAF. 

It was quite nasty, MAF didnt look too bad

Cleaned them both. Oiled the air filter and put it back together, and went for a drive.

No codes came back and fuel trims are much better. Im sure the sticking EGR valve (vacuum leak essentially), and MPFI conversion  fixed most of it but a clean MAF and air filter cant hurt.

Even before fixing the EGR the truck ran much better with the MPFI conversion. It had a much smoother idle and seems to have picked up some lost horsepower. After the other repairs this thing runs excellent. Much smoother. Its so quiet and smooth now that sometimes its hard to tell its running. I really need to change the exhaust. Id like it to be more like a modern vehicle, in that at idle and cruising its very quiet but when you go WOT you get a little bit of exhaust sound.  I think magnaflow makes a muffler that can work with the rest of the stock exhaust system.

Next will probably be tint or a brake hydraulic refresh. So far Im very happy with how the truck is progressing.

A good friend just bought an AWD Telluride and hes curious about the offroad capabilities and Ive been wondering how capable essentially a stock truck like mine is with just slightly more aggressive tires, so we have been kicking the idea around about going to an offroad park and running some of the more moderate trails.

140500 mile update.

The truck has been doing good, just doing truck stuff and driving it. Idles pretty good with an occasional roughness, couldn't tell if it was a misfire, similar to how the LS motors seem to miss at idle but not bad.

Then a week or two later I noticed at hwy speeds I was getting an occasional bucking. I figured it was the TCC lockup, since I've had trouble with that before, but I never got the code back, and finally on Wednesday I got a CEL. Pulled the code and got a P0300. Well that explains it. I figured with a new spider, most common remaining problem is corrosion on the cap and rotor. I didn't feel like pulling it to check only to then put it back together and order one, so I just ordered a Delphi cap and rotor on Amazon and it showed up the next day. It was a shot in the dark since I have an invoice for these parts in 2019, but there is a problem with cheap ones so I guess the probably used crappy parts store parts..

The parts came in Saturday so I pulled the cap. 

Maybe I guess right. So I put the new parts on and fired her up. She idles much smoother. I don't think I can get a better idle out of one of these. I ran it around a little and the bucking seems to be gone. I'll know in a few days, but either way looked like it needed one.

Now that I've got a new spider, and it shouldn't be dumping duel into the crankcase I figured it was time for a good oil change. So I grabbed a filter and a couple quarts of magical unicorn oil. It's like franks red hot, I put that E36 M3 in everything.

I ran some oil cleaner for a few minutes and pulled the plug. It looked like diesel oil. Put the new filter on an topped her off. Seems to have about 10 psi more hot oil pressure so that's nice. Don't know if it's just the old oil vs new oil or if it had some crappy, 5 min oil change bulk special in it. After running for a while, it's not immediately black, makes me hope that the inside of this engine may be kinda clean.

Now that I've been driving the 6th gen around, I've gotten used to those bad ass brakes, so I want to do a hydraulic refresh with a GMT800 master next

Update: Just been driving the old girl. Its been doing good, knocking down about 16.5 mpg. Makes me happy because my smaller engined, 2wd, much newer dodge was getting a little less than that. I did manage to break to glovebox and center console lid, so Im on the hunt for those, and today my power steering pressure hose started spraying. I ordered a PS hose, and will put it on in the next few days.

I checked the front end and the lower ball joints have just the beginnning of some play, for now Im just going to monitor them and when they get a little worse, upgrade to the 2500 aluminum arms.

Still want to do the GMT800 master just havent got around to it yet.

Today I hade some time so I installed the new PS pressure hose, changed the fluid a few times and tried to clean up the huge mess it made.

I also ordered some new brake lines since mine looked original and since SWMBO may need to drive this occasionally I'd like her to feel safe, and a normal GMT400 brake pedal can feel a little unnerving to the uninitiated.

New ones in

Old ones

I then sucked all the brake fluid out and wiped out the reservoir again, it was surprisingly nasty after just a few thousand miles, I doubt it was done regularly in its previous life. Then flushed the old brake fluid out of the lines until I was getting fresh Clean stuff at each bleeder.

Afterwards the pedal felt considerably worse than before. I remembered to bleed the ABS and it was noticeably better than before. Feels pretty dang good for a late GMT400 brake pedal. Still has a little more mushy feel than a modern high and firm pedal, but they are very responsive early In the pedal travel and stop the truck well.

I did notice the difference between hot and cold brakes make a massive difference in stopping power, moreso than I'd expect in a decent street pad.

I still haven't adjusted or even checked the rear brakes, and I still want to go through the front brakes and make sure the slides are moving freely and change to a good pad and some new rotors, so I think I've still got some improvement left on the table. I'm starting to wonder if I will end up even doing the GMT800 master, if I finish up the brakes and the pedal gets even a little better, then I probably just pit an new OE style master on and be completely happy with the way it stops and feels.

I did notice the other day my cruise randomly quit working for a few minutes and never bothered to diagnos it, but when I went to bleed the ABS I saw I had a code for the brake light switch. So looks like I need a new brake light switch.

146000 Mile Update.

Truck has mainly been performing DD duties. It has performed fine. I had to grab some drywall for the She-Shed build last a couple weeks ago, and the truck pulled its first trailer under my ownership, trailer is kinda heavy but It only had like 20 sheets of drywall on it so a pretty light load overall. It worked good enough, but it did show some things that are fine putting around town, but Id like to upgrade or fix, so it pulls a trailer a little better. First the brakes, second the steering and suspension. For the brakes Im going to do some high carbon rotors, raybestos truck pads, and K3500 calipers which have bigger pistons and IIRC they dont have the Low drag seals so maybe theyll help a little with the standard GMT400 squishy pedal. After that Ill redo the rear drums with all new parts, probably all stock, doesnt look like anyone carries anything but normal organic shoes, I couldnt find any upgraded friction material readily availble and I dont know if itd actually help or if it would cause bias issues.

I noticed it was leaking oil. Not enough to really ever leave a drip in the parking spot, but I had some wetness under the truck. Appears to be coming from the back of the intake or the V/Cs. Total I lost less than a quart in like 5700 miles. I was delaying doing intake gaskets but Ive known a bunch of these that have lost motors because theyve dumped coolant into the valley. I finally noticed a little coolant loss but didnt see any leaks so I figured it was time. It was a little overdue for an oil change so I figured might as well knock it out now.

I tore it down and to my surprise it already had the upgraded metal gaskets, but the RTV job on the china walls was pretty bad. I cleaned everything up, put some new lower intake and valve cover gaskets on and reassembled. Repair went smooth no real problems. Engine is a little dirty than Id like, but Ill continue to run good oil, and use a cleaner occasionally and I bet next time I open her up shes much cleaner. Did an oil change obviously, I couldnt find rotella T6 5w40 anywhere so I had to use some Pennzoil Platinum 5w30 and a Delco filter.

I had to get a battery the other day. She stranded me. My fault though I noticed a slow crank for a few days and ignored it. She finally wouldnt start and I went and grabbed an ACDelco battery figuring the one in the truck was pretty old. To my surprise it was from 2020. A day or two later I noticed my USB charger draws power even with key off and this thing sits for a week or more sometime. I unplugged it, and will check actual draw eventually but I bet that was it.

I need to get it in the air and pressure wash all the grime off so I can actually monitor it to see if I got all the leaks.

Is your USB charger off the lighter? Is the lighter live all the time? I've re-wired a couple of the lighters in my vehicles so they are key-on only.

In reply to SkinnyG (Forum Supporter) :

It would appear so. As long as you complete the circuit with the lighter or a usb charger its hot.

Ive been spending all my time working on the she shed so the truck has been neglected a little. I decided to do a little work this weekend. I ordered some parts to refresh the front brakes.

Before starting. Standard 20 something year old GMT400 brakes.

I want to upgrade where possible, but on service items (like brakes) I want stuff readily available in local parts stores. I went with raybestos severe duty truck pads, autozone high carbon steel rotors, and whoever rebuilds autozone's calipers. I didnt do normal replacements for the calipers though, they are K3500 SRW calipers. They are the same footprint, but have a larger piston and are supposed to use a standard piston seal instead of the "low drag" setup in the half tons. The low drag calipers are generally considered the root cause of the terrible pedals GMT400s always have, so I figured it was worth a shot, and even if it doesnt help, I still like the idea of having a larger piston and more fluid at each caliper. I think there is something to it though, because its how GM spec'ed the police tahoes.

New pads vs old pads.

An old timer told me that pads and shoes have a two letter code specifying effectiveness when cold and hot, ranging from A-G. Higher being better. I hadnt heard this but decided to check my pads. Looks like my new pads are a FE. So they should work pretty good and a little better when cold. I didnt have the whole series of numbers and letter for the old pads, looks like they could be BBs or Esomethings. Hopefully they are an improvement.

New caliper vs old caliper. You can see the difference in piston size.

only modification needed was to spread the retainers on the inboard pad a little. I think the 1500 calipers use a 2.94" piston and the K3500 caliper uses a 3.15" piston.

Everything installed.

After that I put some new fluid in the reservoir, bled them real quick, did an ABS bleed, then one more gravity bleed to be sure.

I realized I hadnt changed out the diff fluid yet so I did that next. Rear fluid didnt look crazy, just old.

Front fluid was a little more surprising.

Looks like Ive got some water in there.

I let it all drip out, then ran some fresh stuff through until I wasnt getting discolored fluid anymore.

I put the plug back in and filled it up. I should probably look into how this diff is vented, and replace whatever it is. I havent submerged the diff since Ive owned it, but who knows what happened before. Generally when Ive seen them this bad, they were either recently submerged or have a vent problem.

I poked around under the truck, I have a lot less oil leaking now, so I think the intake and valve covers helped. I cleaned it up a little bit, I may have a small leak from the power steering pump, but I didnt really have a trail or much fluid to track so I just cleaned it. I still have a little oil around the bottom of the engine, maybe the oil pan. I had some on the trans pan, but couldnt tell if it was oil or trans fluid, and neither were low so Ill just monitor them until I can figure out whats leaking.

After that I went to test the new brakes.

They made a huge difference, both in pedal feel and actual stopping power. The pedal has the slightest soft spot, but engages much faster than before and hauls the truck from speed much faster. I also did some work on my dads 91 K1500 Suburban today (which has a new master) and the difference was night and day. I still havent done the rear brakes, or even adjust them, and Im rolling on what appears to be the 23 year old 150K mile master cylinder. I was planning on adjusting the rear brakes today if there was a window in the backing plate, but there wasnt and Im not going to pull the drums off until I have all new parts ready to go on. Probably in the next week or two Ill get all my rear brakes parts, and do the rear overhaul. I think because of the mileage Ill probably do a master preventatively and to finish of the brake overhaul, but with the difference the fronts made Im probably just going to stick with the gmt400 master instead of swapping to the gmt800

I finally remembered to take some night shots once I was out away from town and lights to show how the headlight upgrades perform. The only light besides my headlights was a blue sign.

Low beams

High beams

I highly recommend this mod to someone that wants to keep the stock appearance but greatly increase useable light output

In reply to Opti :

I'd read about the k3500 caliper upgrade, but I didn't realize they weren't low drag! I'll have to find a set for my c2500

In reply to Turbine :

That's what I read. I wasn't ever able to verify though. I think it's true because they made a bigger difference than I would expect new but the same style calipers to make

As a guy who likes old small blocks and knows vortec heads are the thing to use and is starting to think about dabbling in EFI, I'm curious about this MPFI conversion you have done.

If you don't mind explaining that a bit, I'd appreciate it.

It seems like project-type folks pretty much avoid the vortec ("spider") generation of fuel injection altogether.  I'm hopeful this conversion you mention might be useful to me in the future (whether in a stock application or in a project).

Thanks!

In reply to ClemSparks :

The vortec motors come with a similar style injection to the conversion but it used poppet valves. The conversion is plug and play but replaces the poppet valves with electronic injectors and moves them away from the intake valve so they don't get so hot.

The vortec motor makes quite a bit more power than a tbi but where a TBI is generally as reliable as gravity the vortec has two major pitfalls. The injection system, where the regulators or lines will leak, and since it's in the intake it's not immediately noticeable and causes all kinds of drivability issues, or the poppets become plugged. Putting a new mpfi conversion is the solution/upgrade. I guess they could still leak, but new is better than 20 years old and however much mileage.

Pretty much every manufacturer making manifolds for SBCs also make one for vortec heads, there isn't a good reason to swap this into something else and keep the spider injection. Mine is a driver/tow vehicle so I didn't want to do any major modifications that would complicate repairs in the future, and I'm not seeking a bunch of horsepower when the rest of the truck is sorted there are some engine mods planned, but nothing crazy and nothing beyond what the stock injection can take

The other is the intake gaskets. Most vortecs I've seen die an early death were because the intake gaskets had failed and dumped coolant into the crank case. They have upgraded metal gaskets. I recommend doing this at the same time as the MPFI conversion, instead of splitting it up like I did.

Even with the MPFI conversion it's still not a great injection system, it takes up a lot of space in the plenum which is already small, hindering air flow, and there are no larger injectors available that I know of for this system. I would only run it in one of these trucks, if putting a vortec in something else use pretty much any other injection system and your probably better off, including tbi.

They do have a solution for the plenum issue, someone makes a plenum spacer which is supposed to make a pretty big difference on these, but most people still convert to the marine manifold (or others) which utilizes convention injectors and mounting location.

Thanks!  I really appreciate your taking the time to explain that all.

Your sentiment seems to line up with the general concensus that the vortec injection setup isn't a good system for adapting into a project build.  I'm with you as well...might as well use it in a stock application (by stock, I mean in a truck...where the factory put one) if you can make it work well for your goals.

Your explanation did a good job of dissuading me from wanting to mess with that setup very much (which I know was your intention ;)).

Vortec heads are great but manifolds to put different things on top of vortec heads are (as yet...for me) prohibitively expensive.   (I've done a couple carburetors on Vortec heads but some day I want to do something EFI)

Update: Im pretty sure I murdered my master cylinder yesterday. Ive been driving the truck since I did the front brakes with no leaks or problems, and yesterday leaving work i went to stop from a slow roll and nothing. Pedal went all the way to the ground and wouldnt even stop the truck from creeping. I threw the parking brake on and limped it back to a parking spot, and headed home for the night.

I slid up under it this morning and I had a ton of fluid at the caliper/hose junction on the right front. Looks like the brake hose bolt loosened up. Not sure how, im generally pretty anxious about repairs and double and triple check everything, but either way my current assumption is it wasnt tight enough and after a few days backed out enough to leak. Im sure it wasnt leaking saturday and sunday.

I tightened the bolt, checked for leaks, then gravity bled everything, and topped off the fluid. It stops but has a considerably mushier pedal than before. Im guessing when the pedal went to the floor on a 150K master I damaged the internal seals, so I added a master cylinder (GMT400 style) to my list of parts for the second half of the brake overhaul this weekend.

Saturday I started on the rest of the brake overhaul, but I had a family members truck to work on first.

Can anyone guess what im doing?

Yay. knock sensors

I did the valley cover, oil pressure switch, knock sensors and harness, and intake gaskets. The engine was a mess. I need to remember to pressure wash it before I work on it again. I finished that up and went to work on my truck.

First time seeing the rear brakes, they didnt look too bad. Shoes had some life, one wheel cylinder had some seepage and the hardware was pretty rusty,

Got everything off, wire wheeled the backing plate then started reassembling.

Adjusted them out and put the new drums on.

Next I moved to the master cylinder.

Bled everything out and did an ABS bleed and this thing stops like a champ now. Pedal feels great and stopping power is greatly increased, over what I started with. Im content in the brake performance and now its time to move on to other systems.

About an hour after finishing I was checking for brake leaks and found a coolant leak. Drivers side end tank is dumping. Sad thing is I dropped a water pump on the radiator and put a pretty big and sharp dent in the core and its not even leaking there. I need to check and see if any of the other GMT400s offer a bigger radiator as an upgrade.

I was looking into a bigger radiator, I read I could use a 3500 rad but would need the shroud also and didn't feel like tracking down a shroud for a 25 year old truck, I'm having a hard enough time finding the k2500 control arms. So I just went with the thickness core available in the stock dimensions.

My truck had about an 1.5" core, and I went with the 2.25" core, which was surprisingly hard to find.

Old one. Cracked

New thicc boy installed

Not sure what I'll do next. I've been wanting to do a magnaflow muffler or tint or upgraded gmt900 body bushings but other stuff keeps coming up so who knows.

If the rear drum adjusters work, the best way to adjust the brakes is find a safe place, accelerate to about 25 MPH in reverse, then slam on the brakes, trying to stop just shy of lockup. Bonus points if you reverse down a hill. Repeat 2-3 times, and your brakes will be far better than they were previously.  Learned that on the Full-Size Chevy forum years ago, and it worked great!

In reply to dj06482 (Forum Supporter) :

I appreciate that. Hadn't heard it before. I'll try it. I think I set them up pretty good, I had quidance from an old timer, but I'll try and report back if it makes it better

149,500 Mile Update

A month or two ago the truck started making a popping. It feels like it right under me. Sometimes it makes it going over bumps, sometimes it makes it when you transition from braking to accelerating. Ive been under the truck a few times looking and havent found anything. I suspected body mounts, because I know some of them have been messed with to install the side steps that arent there anymore, but I dont have the normal cab sag, so Im not sure. I also couldnt actually find anything failed.

I was talking to a buddy and he mentioned he had something real similar that actually ended up being a loose idler bracket. I had someone shake it down and I looked real close at mine, and the new proforged Idler bracket had a little play, that I couldn't feel at the wheel when I shook it down, but made a distinct pop when it moved. I would have got another one or got it warrantied out, but I was short on time, so I ordered the best parts store replacement I could find and put it on.

I rotated and balanced the tires, cleaned up the interior a little and then aligned her.

I'd like a bigger caster split normally but the truck drove fine like that so I left it alone, and I originally set camber a little lower than GM likes and tire wear has been good, so I just had to set toe.

The blower motor has been making a little noise, like a leaf was stuck in it, so I ordered a new one, assuming it was probably the 25 year old original. I pulled out the old one.

Then I remembered how big a problem a restricted evaporator caused on my old dodge, so I figured Id check mine out while I had access.

Im surprised it was this bad. During the summer I checked the AC and temps were very good, and it seemed to blow well. I brushed the evap with a soft bristle brush and blew it out.

Got quite a bit of junk out, so I re vacuumed that side of the cab and put the new blower in. It works normally. It was very mild today and didnt need the HVAC so I have no idea what improvement if any Ive made on the system.

After that I test drove it and the popping is greatly reduced but not gone. Im hyper sensitive to it, so Im not sure if whats left is normal or not. Ill monitor it, but still kind of want to put body mounts on it since the rear one will also get upgraded to the GMT900 mount.

If anyone has ever ran into a similar popping Id like to know what finally eliminated it.

Hey, I'm loving what you're doing with this truck. I have a question, earlier you upgraded to a gmt800 master cylinder and said that was an improvement. When it went bad why did you go back to a gmt400 master cylinder, and not buy a replacement gmt800 cylinder?

In reply to gearheadmb :

The initial plan was to go gmt800 master, then I wanted to see how good a new slightly upgraded system would work with a new gmt400 master. I've gone back and forth on what to do, but I have only installed a gmt400 master that failed shortly after and was replaced with the exact same part that's working fine now.

I may yet put a gmt800 on it to see what difference it makes on a new system.

the gmt800 master is definitely worth it

153,000 mild update. She's been doing good, I've been driving the camaro a lot more, so she hasn't got a bunch of miles, but I do have some updates.

I got a check engine light a while back.

Trans code. YAY. It's the same trans code I got on the way back form Arkansas when I bought it. Initial recommendation was change fluid and see what happens. It went away until just recently. Did a little more research and GMs recommendation is to change the valvebody if the fluid isn't burnt. Everyone else just rebuilds the Trans. I know my trans guy is behind and I figured I throw a 150 dollars and a couple hours time at it to see if I can save it. I wanted a Sonax updated VB but couldn't find one so I ordered one off eBay the guy supposedly uses Sonax parts to update it.

Got the VB down

Interesting, I'm supposed to have 7 check balls, I only see 6.

There it is. Stuck in the seperator plate. I knew this was a problem on earlier 4l60es I didn't know it still happened after 96 or 97

I put a new/updated seperator plate and vlavebody one. Filled it up with fluid, and called it good.

I've also been dealing with intermittent cruise control and I has a stop lamp switch code a while back so I finally decided to change it. Part is cheap, but in the later gmt400s they are a real nightmare to access. I got it changed though

I've still be dealing with that popping over bumps or acceleration and I've been ignoring it so it could get worse and I could actually find it. Decided while i was under there I might as well take a peak.

It felt like it was right under me so I had suspected the trans mount or u joints but had checked them and never found anything. I got under there and started just yanking on stuff....and heard a clunk

It might he hard to tell but the trans to trans mount bolts were loose. I could tighten and loosen them by hand. I tightened them up and the noise seems to be gone.

Im about to go on a long test drive to check the trans thoroughly, but on a quick test drive the trans feels real good, crisp and much less lazy. Not overly hard or harsh, just crisp and responsive. I have no idea if this is from updated parts or fixing broke stuff and restoring oringial performance.