Ok, here goes. I bought my neighbors 1986 F150 (133k) with a 4.9L and a MT. He was getting rid of it because he couldn't solve the misfire. He replaced the distributor, ignition module, cap, rotor, and wires. He also had a guy swap out the 1-barrel carb to see if it made any difference (it didn't).

Upon getting the car, I checked the compression (all between 117 and 136 psi), timing (see below), coil resistances (within spec), firing order, and vacuum checks (all connected; no leaks). The EGR solenoid wasn't working, so I ended up replacing that (the EGR is working). The engine was pretty filthy due to a valve cover leak and the choke stoves were broken, so I ended up pulling the valve cover and manifolds and replacing the gaskets, fixing the stoves, and cleaned/painted everything. One of the push rods (#3 exhaust) was bent, so I replaced it. I didn't notice anything abnormal with the lifter/rocker.

Upon putting everything back together, it didn't make much, if any difference, but it looks nicer . So here's where things got interesting:

Timing: I originally checked the timing with the SPOUT connected (wrong) and it was at like 14 BTDC. I adjusted it to 10 BTDC with the SPOUT connected before I did the above work and noticed little change. After I did the above work, I checked/adjusted the timing by disconnecting the SPOUT, and it seems to run a lot better with the SPOUT disconnected. It is pretty smooth, but I still get a blip in the RPMs every 10-15 seconds. However, when I plug the SPOUT in, it runs like crap and the idle is all over the place. When it warms up fully, it wants to stall at idle.

I then proceeded to check for trouble codes. For the KOEO, I got an 11 hard (pass) and an 18 memory (SPOUT) which I am guessing is due to setting the timing. During the KOER test, I got a code 41 . I rechecked my vac lines and then did a fuel volume test and got >1/3 pint after 10 seconds of cranking. I did not do a fuel pressure test because I don't have a gauge. I decided to just replace the O2 sensor, but you guessed it, no change. The old sensor does rattle pretty good when I shake it though.

Does anyone have any ideas/advice? I am trying to wrap my head around how the SPOUT being connected makes it run terrible, but I only get a code 41. Whoever installed the distributor could have stabbed it a tooth off, but would that draw a code 41? I have the Ford manual and came across the thread below, but I am looking for input on whether this could be 1 problem or 2 independent problems.

https://www.ford-trucks.com/forums/1...back-carb.html

 

I think you should check for a bad computer before you chase your tail any more.

Caps go bad all the time and if you catch it before they corrode the board it is cheap to fix.

 

41 is a lean code. When the spout is plugged in and the engine is running lousy, can you cover the carb with your hand to restrict the air to the engine and it smooths out? That would also verify the oxygen sensor is not lying, you do have a lean condition.

 

I would wonder about the bent pushrod.

 

I pulled the computer tonight and looked didn't notice any leaking/swollen capacitors, burnt components, broken solder joints, etc. Are there any other "checks" that I can do?

I did this once today, and it wanted to stall right quick. I will have to verify this tomorrow because I'm not sure if I had anything unhooked when I did it.

Me too, but unfortunately I don't know if anyone over-revved it since it came as a basket case. I didn't notice any immediate difference post-swap.

Today/tonight, I did do a few more checks based on the previous owner thinking the smog pump was bad:

• The smog pump belt was a little loose, but it is pumping air (tightened the belt).
• I pulled the diverter/bypass valve and that checked out ok as well as the check valves.
• I triple checked my vacuum lines (all ok) as well as the vacuum from the TAB/TAD with the exception noted below.
• I checked the TAB/TAD solenoid V/resistance and both checked out. I have a spare set that I swapped in momentarily just to make sure (no difference).
• I disconnected the exhaust after the manifolds (no difference).
• I rotated the distributor some to compensate for it potentially being a tooth off if someone stabbed it incorrectly. It sounds best near 10 BTDC.

However, I did notice the following:

• When I hook the timing light up (red to positive, black to ground), the engine wants to stall/idle gets really rough when I pull the trigger. When I hook it up to the battery instead of ground, it doesn't. This seems very bizarre to me. I measured 14.45v across the battery and to the frame when the engine is on, 12.6v when it's off. Thoughts?
• The engine seems to run smoother at higher rpms (1500-2000) but still blips. After kickdown, it drops to about 550 with the SPOUT connected, but only about 750 with the SPOUT disconnected. Does that seem low?
• TAD Vacuum: It doesn't seem to be dropping as intended (100-180s after start). When the idle is low, it is pretty rough (borderline stall), the needle is all over the place.

 

I would check the vacuum advance to see if the diaphragm is bad. Suck on the hose with the advance still plugged in. If the diaphragm is good, it will hold a vacuum. If it is bad, it will be like a vacuum leak and cause the engine to run rough.

 

But if there's a spout how can there be a vacuum advance on a distributor with tfi?

 

It is computer controlled.

 

you've never said you set the timing with the spout out, I assume you did but just had to ask.

 

The first time I didn't, but subsequent times I did. When I check the timing with the SPOUT disconnected, I'm at 10 BTDC as required. When I check it with the SPOUT connected, it only advances a few degrees (like 16 or so). The FORD manual indicates I should be at 30 degrees +/- 3 degrees which is way off. I spent a decent amount of time last night with the engine running and the SPOUT disconnected, and I think I was off with my initial assessment that it runs better with the SPOUT disconnected; it seems to run just as bad when it idles down.

Does anyone find it odd that if I hook the negative terminal of my timing light to ground it makes the car want to stall, but if I connect it to the battery it doesn't? I can have it connected to the frame, but as soon as I pull the trigger to turn the light on, it wreaks havoc on the idle.

 

Check for a ground wire from one of the bolts at the back of the engine to the firewall. If it's not there I would add one. You can temp hook a jumper cable from the battery negative to something metal on the cab sheetmetal, and then see if it still does it. You may have a grounding problem with the computer or something in the cab. Obviously the ground from the battery to the engine block is good since the starter works. But you should have a ground from the engine block to the cab sheetmetal. The cab is mounted in rubber cab mounts.

 

Just a little
Is the timing light the type that goes around the plug wire (induction hook up) or the type you pull the wire off the plug and the light goes between plug and wire?


Also because of what you said of the way the light is working and this miss that cant be found and fixed I think now would be a good time to check ALL GROUNDS. I would start at the batt pos, pull and clean the connections there and work my way to the starter solenoid> starter.
Then Batt neg> motor side> motor to frame> motor or frame to body.


Then maybe pull the computer to make sure where it bolts to the body is clean and has a good ground. Also if the computer has a ground wire in part of the harness see if that has a good connection.


Checking the above just takes time no money unless you find bad batt. cables. Me if and the cables look in question I just replace them.
Yea I know they can look good on the outside and be bad on the inside and why most of the time I just replace them any way.


I also question the bent push rod?? Could the cam lobes be going flat and why the miss? Yes compression can be good and have a bad cam.


FYI my 02 Dodge 360 had a miss at idle and everything checked out good. The dealer replaced a lot of things as per the factory and still had a miss they did a leak down test and found bad exh valves that a compression test did not pick up. When they pulled the heads for a valve job they found cracks, motor was never run hot or over heated.


Dave ----


edit: I see the Dave's are thinking the same ----- grounds!

 

OK, this just a shot in the dark.

I just got a 1972 International Loadstar 1700 with a 392.
It ran and started fine but had a misfire we couldnt correct. So we pulled the valve covers to find out we had a Flattened camshaft. The truck ran Great, had power, but the passenger front cam lobe on the exhaust side was flattened, causing a backfire/misfire.

Is this something you have checked yet? we assume the cam lobe on the 392 was flattened from sitting for years, then was dry started. (not by us)
We got the misfire/backfire to stop by grounding the wire to the block as a temp solution to get it home.

This is not something most people think about, and i have 0 experience with the 4.9L 6's, so i dont even know if this may be a possibility, but worth mentioning IMO.

 

Problem solved. The previous owner installed a distributor from an 87-91 for an EFI 4.9L. I needed one for an 84-86 for a carbed 4.9L. The vane cup is different and created a Signature PIP signal when I needed a PIP signal, so I'm sure the computer didn't know what was going it on.

I swapped out the vane cup and it ran a lot smoother, but the RPMs still blipped slightly randomly and still had issues when I connected the timing light to the frame. I swapped out the Ignition Control Module and it runs perfect and the timing light no longer causes the engine to bog down when I connect it to ground. Extremely weird, but glad it's fixed.

I appreciate all the input and thoughts. I apologize on not updating my progress, but it took a while to get the correct vane cup.

Thanks again!

https://www.ford-trucks.com/forums/1...l#post16712642

 

We thank you for working it out and getting it fixed and the big one posting what the fix was so if someone does a search and comes across this post they may fix theirs too.


Dave ----