Misfire at idle 300 i6 f150

[Nessism1]

When Ford stopped making the straight-six in 1996(?) at the Cleveland engine plant, it was like a funeral precession all through the area. Ford had a massive presence in NE Ohio, and many people were associated with that project.

 

[nwjones18]

Try blocking it off entirely. IIRC a quarter or an electrical box KO might work -- don't remember if 1/2" or 3/4"

Not sure how it would affect his OBD II truck, but on my 88 I unplugged the EGR and capped the vacuum line with a golf tee somewhere around 2004 planning on doing something better later... Its still like that and running great. If I recall I was having problems with the truck having lean sounding 'coughs' at idle and eliminating the EGR cleared that up.

Also if you have dual tanks the selector valve can cause some weird issues where you have fuel pressure sometimes and not others.

 

[D60]

Not sure how it would affect his OBD II truck, but on my 88 I unplugged the EGR and capped the vacuum line with a golf tee somewhere around 2004 planning on doing something better later... Its still like that and running great. If I recall I was having problems with the truck having lean sounding 'coughs' at idle and eliminating the EGR cleared that up.

Also if you have dual tanks the selector valve can cause some weird issues where you have fuel pressure sometimes and not others.

I did something similar on my '90 351. But here I'm wondering if his EGR valve itself isn't just stuck open a crack. It clearly isn't stuck because he can actuate it but it may not be fully seated when closed. Since it's easy enough to test this theory, I'd give it a shot if it were me.

As noted, one of the most common culprits of funky idle on EEC-IV is the EGR

 

[Orangepeel]

I cannot see the egr pintle through the intake.
Long term fuel trims are +25 but short terms are between 0 - +5.

 

[OVERKILL]

I cannot see the egr pintle through the intake.
Long term fuel trims are +25 but short terms are between 0 - +5.

You can just take the valve off and take a look at it. They get crusted up and leak exhaust into the intake because they don't fully close.

 

[Orangepeel]

Pulling the spout connector seems to have totally alleviated the issue. So where would you got from here? Tfi pip or pcm?

 

[Orangepeel]

I decided to check the pcm I don’t see any issues with it. Doesn’t look burnt. Capacitors look good. Can I assume it’s good?

 

[Chris142]

I had a 302 Chevy that did weird things idling. Turned out to be bad valve guides letting the valves wobble around and not always seating on the seats correctly.

 

[Mcbeem5]

2) these engines are old enough to have the TFI (thick film ignition) modules. Those were suspected to have issues as they age; the ECU would essentially misfire occasionally because of internal signal leakage in the unit itself, or something like that. And they have external components which also can cause issues

Back in the 80s I had a Ford Escort with 10,000 actual miles got towed into dealership,mechanic said Ford had alot of problems with TFI modules.

 

[ripcord]

2) these engines are old enough to have the TFI (thick film ignition) modules. Those were suspected to have issues as they age; the ECU would essentially misfire occasionally because of internal signal leakage in the unit itself, or something like that. And they have external components which also can cause issues

Back in the 80s I had a Ford Escort with 10,000 actual miles got towed into dealership,mechanic said Ford had alot of problems with TFI modules.

I think it's basically impossible to get a new TFI module that isn't Chinese junk any longer. I keep a spare in my F250. Most auto parts stores have mistakes in their databases, too, and will sell you the wrong part for some models.

 

[D60]

Verified timing with the SPOUT removed? I'm not sure this would cause your issue but if someone recently crammed a cheap dist in there I might wonder about that.....?

 

[Orangepeel]

Here is a video of the egr valve function. Not sure if how it seems slightly bent is normal or not.

 

[OVERKILL]

Here is a video of the egr valve function. Not sure if how it seems slightly bent is normal or not.

Yeah, that looks to be doing a bit of an angle there. I'd hit it with something that removes carbon. I used to love the AC Delco combustion chamber cleaner for that purpose, if you can find it, otherwise something like B12 will do the job.

With the impact of the SPOUT pull, you should check your base timing. IIRC, it should be 10 degrees base. Do you own a timing light?

 

[Orangepeel]

I do I guess I can dust it off and use it. Scan tool reported about 12 degrees though.
I hesitated to do that because the ltft being +25 that made me wonder if it was a vacuum leak or something a long those lines. Short term fuel trim has been as high as +12.

 

[Chris142]

Check valve lash, especially exhaust.

Not adjustable

 

[D60]

I do I guess I can dust it off and use it. Scan tool reported about 12 degrees though.
I hesitated to do that because the ltft being +25 that made me wonder if it was a vacuum leak or something a long those lines. Short term fuel trim has been as high as +12.

Well if the EGR were feeding exhaust gases, would it not also attempt to dump more fuel to compensate?

Exhaust gasee are already spent, but it's still a gas adding to the intake mixture.....I'd think?

 

[ripcord]

Well if the EGR were feeding exhaust gases, would it not also attempt to dump more fuel to compensate?

Exhaust gasee are already spent, but it's still a gas adding to the intake mixture.....I'd think?

No, the exhaust gasses reintroduced into the intake by EGR are mostly depleted of O2 so so no additional fuel needs to be added to the mix. The exhaust gas has the effect of diluting the oxygen in the intake air charge so the EGR has the opposite effect of what you're thinking.

 

[Orangepeel]

Not sure how scientific of a test this is. But I filled the the valve face on the egr valve up with brake clean and it did leak last and down to the stem pretty quick.

 

[OVERKILL]

Not sure how scientific of a test this is. But I filled the the valve face on the egr valve up with brake clean and it did leak last and down to the stem pretty quick.

Yeah, so get cleaning that puppy and see if that helps. BTW, 12 degrees sounds low with the SPOUT in, not that I trust the scan tool over a timing light. We used to set the 302's to 14 initial, which was in the 20's with the SPOUT in, IIRC. Would wake them up a bit over the stock 10 degrees, but required 91 octane not to ping with that much advance.

 

[Orangepeel]

Yeah, so get cleaning that puppy and see if that helps. BTW, 12 degrees sounds low with the SPOUT in, not that I trust the scan tool over a timing light. We used to set the 302's to 14 initial, which was in the 20's with the SPOUT in, IIRC. Would wake them up a bit over the stock 10 degrees, but required 91 octane not to ping with that much advance.

A new one was 45 so I ordered it. Figured since I’m removing it might as well have a new one . Of course with that logic the whole darn truck might be new soon