Mr_Asa New Reader
1/10/20 5:27 p.m.

So, March-ish I had to replace the engine in the DD, a '93 F150 4.9L Inline Six.  While I've built engines before, this was the first engine I built wholely on my own with no help from anyone, so I may have berkeleyed something up good and proper.  Doesn't completely feel like it though.  Mods include a slight compression bump, mild cleaning of the ports, Chevy I6 rocker arms (to go from 1.6 to 1.7 ratio), and an old MSD 6A box a friend gave to me, so nothing crazy.

Symptoms:  Runs decent at startup, runs great at anything above idle, idles okish when cold, idles like dog E36 M3 when its hot.  

Thoughts: I'm not 100% confident on the valve seals or the valve adjustment, although it has hydraulic lifters and there was the same amount of play on each rocker arm.  This issue in cofidence is due to my inexperience with installing any sort of internal mods on the vehicle.  In the pictures below, the ugly one is #5, don't be fooled by the oil on the outside of the plug as that came from spraying the cylinder with brake clean during an initial no-start condition when I installed the engine and the nastiness getting on the plug's exterior.


EDIT: Ok, so it seems that I need to update the symptoms.  When its hot, if I haven't been on the highway/interstate it doesn't run poorly.  Small hiccup as if its got an intermediate miss, but nothing like when its actually idling horribly.

The idling horribly is similar to a carb'd motor that the idle is set too low, like its about to shut off.  No surging with it, it doesn't catch up and run well, it just sort of almost constantly dies

Shadeux Reader
1/11/20 6:45 a.m.

As to the hot idle I would look at fuel or vacuum.

Is that enough gap for a MSD 6A?

Paul_VR6 Dork
1/11/20 6:49 a.m.

I would start troubleshooting vacuum leaks, idle valve, and sensors related to efi (coolant/air temp)

Dr. Hess
Dr. Hess MegaDork
1/11/20 7:40 a.m.

#5 is burning oil.  Why?  Valve guide?  Seal?  Rings?  Did you do a leak down or compression test?


I would also look for a vacuum leak, such as manifold to head in particular, or maybe injector seal.  When idling (hot and not well) spray a little carb cleaner around all gasket areas.

Toyman01 MegaDork
1/11/20 8:21 a.m.

Got any video of it running like crap? Might be valve lash tightening up as the engine comes up to temp. 

Mr_Asa New Reader
1/11/20 8:32 a.m.

I'll start checking for vacuum, and do a leakdown and compression test.

In reply to Shadeux :

I was told 45 for the gap.  Think I should go with more?

In reply to Paul_VR6 :

Of the sensors and solenoids, only two are old (and those are from a running engine.)  Old sensor is the knock sensor, old solenoid is one of the EGR vacuum vent/purge solenoids, only reason it remained on there is because I haven't been able to find one to replace it.  Doesn't mean that these new sensors are good out of the box, but its rare for me to find one that isn't.

In reply to Dr. Hess :

The oil burning is almost more of a concern to me than the idle.  I can live with the idle since it runs well at speed, but a newly rebuilt engine shouldn't be burning oil.

Mr_Asa New Reader
1/11/20 8:32 a.m.

In reply to Toyman01 :

I'll try to get one later today

Curtis73 UltimaDork
1/11/20 9:20 a.m.

I would think a gap would be more like 050-052, but I don't think that's the issue.

Sounds to me like a vacuum leak or a valve not closing.  On a vacuum gauge that would show up as pretty wild fluctuations.

But I have to say, congrats!  That is a major accomplishment.  The first one I built was a BBC and the cheers and screams that came out of my mouth when it fired up were almost as loud as the open headers.  Good job.

Mr_Asa New Reader
1/11/20 9:32 a.m.

In reply to Curtis73 :

I think I've got a vacuum gauge I can plug in somewhere.  I'll dig it up and see what she's doing.

Thanks! I'd feel better about the swap if I hadn't had such a stupid screw up during the build.  The 300 uses timing gears.  To time the cam and crank, you just line up two dots.  I did that, I remember doing that because it took two or three times to line them up properly as I kept getting one tooth off.  Got it in, took a pic cause I liked the look, put the build on pause for a couple weeks while I dealt with other crap.  When I came back to the build I realized I needed to remove the crank or cam for some reason or another.  Did so and put it all back together.  Somehow in that, I got the cam and crank 90 degrees off from time.  After I got the engine in, it took me two or three weeks of trouble shooting to try and figure out what was going on because I was so adamant that the cam timing was good, after all I had a picture of it being right.  Finally I broke down and pulled the timing gear cover to find this.  It really shook my confidence in my skills and how good the engine was going to be.

gearheadmb SuperDork
1/11/20 10:04 a.m.

I had the exact same symptoms after installing a head gasket on a different engine that overheated. The problem ended up being that the head warped causing the valves not to seal. I was pointed in the direction of that diagnosis by the vacuum gauge fluctuating wildly as mentioned above, so yeah, vacuum check and compression check is where I would start. It was fixed by getting the head milled and a valve job.

No Time
No Time Dork
1/11/20 10:05 a.m.

How was it running before the rebuild?

When you did the rebuild, what did you do for block prep?

How many miles on the engine since the rebuild?

I'd pull all the plugs and check compression. 

Then I'd check valve lash hot. Make sure it's not overnight or a dead lifter.

as for the oil, I'd wait to see what compression tests and valve lash shows. If the intake isn't opening enough on that cylinder it will pull oil past the rings  




Mr_Asa New Reader
1/11/20 11:33 a.m.


Please see the edit in the first post.  Did some running around this morning to complete some honey-do errands to get it up to temp to try and get some videos and more things for diagnostic support.  Doesn't idle poorly.  I'll try and get her on the interstate in an hour or two.

In reply to Curtis73 :

Vacuum at idle, hot with the mild miss I mentioned in the edit is a rock steady 18-19 inches.

In reply to gearheadmb :

Head and block were milled, valves were checked out and were not in need of any touch up except for cleaning up the seats a hair and lapping them in.  Machine shop did this.

In reply to No Time :

I couldn't afford downtime with this, so the engine was (supposedly) a runner but was pulled from a farm truck that the owner's brother had accidentally dropped a tree on the bed.  Was an '87 or '88, I tore it down and other than some slightly excessive wear in the main bearings and some horrendous oil buildup I didn't see anything horrible.  Machine shop put it through their cleaners and got it looking great before they checked everything.  Standard bore, standard main bearings, new cam bearings, milled head, decked block (both lightly done) etc etc.  Nothing stood out.

At least 8K, probably closer to 10K, I'll check my logs.  I noticed this starting to show up maybe 4-5K back?

iceracer UltimaDork
1/11/20 11:47 a.m.

After revisiting the spark plugs, why does #5 show residue/oil all the way up to the boot ?

Could you have missed tightening it properly ?

No Time
No Time Dork
1/11/20 12:42 p.m.

In reply to Mr_Asa :

Good info that it ran well after the rebuild and this is a new issue. 

First thing I notice is the center electrode on plug 5 looks odd, either buildup or something strange going on there. I'd put in a new set of plugs, and maybe go with champion since I've never had good luck with autolites, even when I had fords.

Can you pull injector wires or plug wires one at a time with it running to confirm the cylinder that is missing? Then see if moving the injector causes the miss to follow the injector.





Mr_Asa New Reader
1/11/20 2:49 p.m.

Ok, nice highway drive, got the crappy running symptoms.  Cruising I'm seeing 3-5 inches.  Idle in gear is 14-15 inches (as opposed to 18-19 inches when cold,) idle in neutral/park gets back to 18 inches.  In park right now its not as huge an issue as it was, but still feels like a miss.

Had a CEL pop up while I was driving then turned itself off.  I'll see if I can find my code puller and see what it was.

In reply to iceracer :

Those are the original plugs when I was trying to figure out why it wouldn't initially start (see my reply to Curtis73 five or six posts above.)  Dropped it off with a friend and he and a couple guys poked at it, one of them did a compression test and ended up getting a E36 M3load of oil and crap in the well of the cylinder head.  Couple thousand miles of driving in Florida weather with rain and such and all that crap gets smeared all over.

I changed the plugs before posting this thread and all of them were at about the same torque level.

In reply to No Time :

Yup, there's definitely carbon build-up on that electrode.  Burnt oil?  Dunno.  I did put in new plugs.  Was better for the first drive to work, back, and next day's drive.  That was Tuesday morning, since then we're back where we started.

Can pull plug wires, but moving the injectors easily and quickly is not really a possibility, I'll do that last if I need to.

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