Brett_Murphy said:The Terrible Truck in its natural habitat: On jack stands.
You can see the dent where the tree was growing into it near the back wheel, just in front of the bed. I just plan to tap that out.
Not that this helps with your problem, but it is a good looking truck dent and all.
I don't think it ever drops to zero on purpose. Not that sophisticated
In reply to Dusterbd13-michael :
I was afraid of that.
What is the condition that causes the drop?
Stepping on the throttle more than a wee bit when the engine is warm. It'll do it about half the time when the engine is cold, too.
I posted a video of it happening working the throttle linkage- I may be able to get a better video if you can't see that one well.
Ah. I see the video now.
Unplug sensors one at a time and repeat the throttle test. I THINK you have a tps issue, or possibly map. Only time tbi cuts fuel completely is on deceleration. So, if its sensing decel....
TPS is brand new- like, 5 miles on it. That's what I though it was first.
The MAP's connector broke when I tried to take it off this time. When it was disconnected, it ran like crap and I threw a check engine.
When I put it back, it ran correctly for 15 seconds, then went back to being stupid. That's a new result- last time disconnecting it made no difference, but if the connector has been shot, maybe it's not making a connection.
I'll replace the MAP, just to eliminate it.
Brand new MAP and connector- same issue.
To recap:
1. Good fuel pressure
2. New fuel filter
3. New TPS and connector
4. Fuel pump has 150 miles on it
5. Good vacuum
6. Rebuilt TBI
7. New plugs, wires, distributor, ignition module (forgot that in the last recap)
8. New MAP and connector.
Truck starts and idles fine. While very slowly pressing on the gas in park, if I try to go more than 1/4 throttle, it will surge, then if I keep pressing on the gas, it will cut out. If I immediately let off of the gas, it will keep running, idle fine, etc. This is happening with the engine both cold or warm at the moment, and also happens when in gear.
Grasping at straws....
Have you tried wiggling all the wires in the harness while it's running, so see if there's a bad connection? Could be something eaten by a rodent, or just a bad splice for sensor ground(s)?
Can you build an ALDL cable, and datalog using TunerPro?
(TunerPro is free, and making an ALDL cable is easy-peasy).
I've wiggled the wires, but that doesn't mean there isn't a bad connection upstream. Though, given how incredibly consistent it is, it doesn't strike me as a loose wire- it happens the same way under the same conditions every time.
I'll look into an ALDL cable, though I don't have a portable computer to plug it into- maybe it will work with my Android tablet.
I may just punt the diagnostics at this point, though- I'm getting very frustrated.
True, if it's staying hurt, it's gotta be something significant.
If you can read a datastream of input, you could at least see what it's doing - less guesswork and parts throwing.
I followed this: http://winaldl.joby.se/ and tried using WinALDL on the '88 F-Body TBI I had in my Firefly, but WinALDL was pretty slow (so was the ECU, for that matter).
ALDL instructions were here: http://winaldl.joby.se/aldlcable.htm and I used the self-powering second version. I left it in the V8 Firefly when I sold it.
https://www.tunerpro.net/ and you'll need the correct BIN or MASK or whatever it is that you need to be able to read what's going on.
And of course, the next step will be heading over to Moates for a chip.
Or just go Megasquirt. Or Carb.
I don't know if this will be of any use, but I took some scans of relevant sections (fuel system diagnosis, stalling) from my TBI vette shop manual. Peruse at your leisure.
https://www.dropbox.com/s/cf82hrnaz29kzyj/1984%20corvette%20fuel%20system%20diagnosis.pdf?dl=0
My experience with my 88 TBI truck may not be of any relevance to yours, but I'm going to share it, just since it's so weird.
My truck would get no pulse to the injectors when cranking, but would run normally if primed. Turned out to be the distributor.
Have you tried actually driving it to see if the problem still occurs? I seem to remember my parent's Buick of about the same vintage having a similar issue. The computer would only allow for a certain max RPM while the vehicle was in park or neutral, and pulled fuel if that RPM was reached. As their car aged, it would die if you revved it in P or N, as the computer management was no longer handling things correctly. Of course, this was a totally different engine, make, etc, but you never know how much GM shared between divisions.
Hmmm. That could be worth a test. The TBI needs the VSS to know that the car is moving, and it manages the fuel and ignition differently in gear than in P or N. You could just make the switch always "see" Drive, and see if it makes a difference, ALTHOUGH, the TBI computer I messed with would totally drive (relatively) fine with the switch either thinking it's in P/N or in D, and it still drove fine (not the problem you're having here).
It happens when moving- and, given where I live, I'm trying not to drive it on the streets much, because I'll get killed if I step on the gas and nothing happens.
If it's an issue with the VSS you should be popping a code that follows that.
Is the speedo electronic, and does it work?
I think the speedo is analog, and it works.
It's one of these:
Here is an interesting thought-
Could the fuel pressure regulator be opening and just allowing the gas to go down the return line? It's a pretty simple system, being just a spring and a valve.
I'm not sure how to test that, since it's nothing but hard lines, and I can't pinch it to block it a bit.
We hit a point where I thought: Well, let's start over.
The fuel tank seems to have disintegrated internally. It had very little gas in it when the truck was sitting, and we drained everything and the fuel tank looked alright with a visual inspection, but apparently driving the truck around knocked a whole bunch of crap loose. So, everything is kind of berkeleyed up, fuel system wise.
A new fuel tank, pump, straps, fuel filter, etc. will run maybe $500. I'm thinking that I'll do that, and start collecting parts for an LS Swap, too.
Could you get just a tank assembly, and filter? Lines should be fine, same with straps. May have to disassemble the tbi and clean the injector screens too.
My plan is to get in there and start seeing how bad it is before I order the parts. We'll see.
Huh... a bit of searching at lunchtime shows that LT1 setups are $300 these days.
Considering how much schmutz the fuel pump apparently drew into the sock, I can take a guess at what happened. Apparently at idle it wasn't drawing enough gasoline through the system to cause an issue, but when I opened the throttle, the act of drawing more gasoline was sucking all of the E36 M3 up against the sock and choking itself out.
A brand new gas tank was a bit more than $100 for a C1500. Bottom line: Truck is running great now. I took it for a good drive and... the passenger side wheel cylinder is leaking. There's another $12 per side and an hour of work.
Now that it's running fairly well, I can start addressing the front end. Everything feels a bit sloppy there.
I'll post a picture of the fuel sock as it came out tomorrow.
Even though the Terrible Truck is still under budget, as all of these repairs count as "replacement with non-performance enhancing parts*, I don't think it will ever be a Challenge car. We'll see. I really got to work on the Camaro if that's going to be the Challenge car, though.
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