Misfire at idle 300 i6 f150

[Lubener]

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

I wouldn't. I have seen many 300's start pinging when the EGR was omitted or wasn't working at all. Best to repair or replace. If he has emission testing, it won't pass the NOX portion of the test without a working valve.

 

[Lubener]

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

Best move along with a new EGR gasket.. Hopefully you were able to break loose the pipe without it breaking. They are hard to come by.

 

[emmett442]

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.

Not 100% on this one, but usually with these old ignition systems, base timing is assumed and the reported number is what's added/removed. With base timing assumed, the computer has no idea where total timing really is.

For example, if reported is 12 and base is 10 in the computer's tune, you have 22 total as a target. Because computer doesn't know where the base timing actually is, if you have base set to 14, you actually have 26 while reported is 12.

That said, the computer targeting 22 at idle in this case seems reasonable to me.

 

[OVERKILL]

Not 100% on this one, but usually with these old ignition systems, base timing is assumed and the reported number is what's added/removed. With base timing assumed, the computer has no idea where total timing really is.

For example, if reported is 12 and base is 10 in the computer's tune, you have 22 total as a target. Because computer doesn't know where the base timing actually is, if you have base set to 14, you actually have 26 while reported is 12.

That said, the computer targeting 22 at idle in this case seems reasonable to me.

OK, I wasn't sure if his tool was thinking it was reporting total or deviation from base, but in either instance I think he's probably well-served checking it with a light to verify.

 

[Joba27n]

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

Replace the distributer is what I do at that point

 

[Joba27n]

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

Long term trims of +25 is saying the engine is running very lean and adding alot of extra fuel. I'm surprised the truck hasn't thrown a lean fuel trim code yet.

Assuming thats your fuel trims at idle, what do they do when you hold the rpms at say 2500-3000 rpm?

Also is this a speed density engine(MAP only) or MAF equip engine? If you have a MAF, what does it read at idle speed with the engine warmed up?

 

[Joba27n]

Replace the distributer is what I do at that point

The "cam sensor" is apart of the distributor and i've found when they start to fail the pcm "misses" the signal to trigger the coil and you get that mis-fire

 

[OVERKILL]

The "cam sensor" is apart of the distributor and i've found when they start to fail the pcm "misses" the signal to trigger the coil and you get that mis-fire

You can test the functionality of the hall effect sensor with a scope or even a timing light though, so it's pretty easy to verify if this is in fact the issue.

 

[D60]

Also is this a speed density engine(MAP only) or MAF equip engine? If you have a MAF, what does it read at idle speed with the engine warmed up?

In Post #5 OP says MAF readings are correct and he cleaned it, so I'm ASSuming the 4.9 did in fact go mass air in '96 like the small blocks.

I think allegedly in certain cases like CA emissions some of the OBS trucks got mass air even a year or two before '96, but I've never witnessed one. There's a lot of urban legend and internet mythology here and I don't know what the truth is. I'm even more curious about reports of MAF 460s, but that rabbit hole won't help the OP.

 

[Mcbeem5]

No one has mentioned this but I remember on old school distributer caps --getting Carbon Tracking-- and this can lead to a low speed misfire! Try and NEW Distributer Cap and Rotor!

 

[ripcord]

You can test the functionality of the hall effect sensor with a scope or even a timing light though, so it's pretty easy to verify if this is in fact the issue.

I think if you want to use a timing light to check the Hall effect sensor (or crank position sensor in Ford's terminology) you have to use a low current LED type test light. A regular test light has too much resistance and takes too much current.

 

[OVERKILL]

I think if you want to use a timing light to check the Hall effect sensor (or crank position sensor in Ford's terminology) you have to use a low current LED type test light. A regular test light has too much resistance and takes too much current.

If it's randomly misfiring, you should be able to pick it up on the plug leads using a standard light, and this will show whether it's only happening on a specific cylinder/cylinders or if it's all cylinders affected, pointing to the trigger (which also controls injector pulse).

If, as you note, you want to test the sensor signal itself, you can't use a standard timing light, but you can use a multimeter, low current LED light, as you note, or, a scope (most preferable of course, to see the waveform).

 

[Orangepeel]

Egr didn’t fix the issue.
Long term fuel trims at idle are +25 when you get the revs up some they get closer to 0. Usually +3-7 which is pretty decent I feel like. So I’m unsure of why at idle the ltft are so far positive.

 

[97prizm]

At idle I’ll get a hiccup every now and then on my 96 f150. New tune up (complete) just done and no change. Seems to affect all cylinders when I watch misfire counters it’s 3 and 5 most often but they all miss every now and then. No vacuum leaks, fuel pressure is good and it runs good and doesn’t miss when driving it. Only sputters at idle every several seconds. Where would you go from here?

I just got done going in circles with my Chevy cavalier. After three sets of injectors and two sets of plugs new wires and an Iac valve it finally passed emissions and now runs well. A couple of the original injectors had a leak. My dad and I replaced just those but got a misfire. The junky amazon no name injectors got it to pass emissions but it would die at idle. I found a cavalier at a pull n pay that had a ton of new parts. So i pulled the injectors, wires, and air filter hose. It looked like it had a major overhaul before it was crashed. The intake and old iac valve were really dirty. I sprayed a ton of cleaner through them then installed a new iac and while not perfect drives better than it has in a while.

 

[Orangepeel]

so checking timing with a timing light is a blast on this truck. The timing marks aren’t there like on the older ones. That being said scan tool reports 10 degrees with spout connector unplugged. At this point I don’t think it’s ignition. The long term fuel trims make me think it’s a fuel issue or possibly air but I’m at a loss.

 

[ripcord]

High LTFT at idle only? Have you checked the Idle Air Control valve? Try unplugging it at idle and see if the idle changes. Also take it out and check and see if it looks gunked up. Maybe there is some carbon or grit not allowing it to close fully, allowing too much air in at idle.

 

[t1snwrbrdr12]

so checking timing with a timing light is a blast on this truck. The timing marks aren’t there like on the older ones. That being said scan tool reports 10 degrees with spout connector unplugged. At this point I don’t think it’s ignition. The long term fuel trims make me think it’s a fuel issue or possibly air but I’m at a loss.

Unsure how accurate relying on the scan tool to read timing is, I assume it’s more so than your eye on a timing mark but idk. Can you get at the timing mark with a tire crayon or white out to mark it so you can see it? Are you missing the pointer? Why can’t you check timing, that’s a little confusing.

It also sounds like a vacuum leak, how do you know you don’t have one? Have you sprayed brake clean / gum cutter around to watch fuel trims or see if it stumbles at any point where you spray?

 

[t1snwrbrdr12]

Is it humid where you’re at? Have you tried spraying ignition components down with water while it’s running?

 

[Orangepeel]

Unsure how accurate relying on the scan tool to read timing is, I assume it’s more so than your eye on a timing mark but idk. Can you get at the timing mark with a tire crayon or white out to mark it so you can see it? Are you missing the pointer? Why can’t you check timing, that’s a little confusing.

It also sounds like a vacuum leak, how do you know you don’t have one? Have you sprayed brake clean / gum cutter around to watch fuel trims or see if it stumbles at any point where you spray?

They don’t have the regular timing marks on the balancer. The little tiny notch is almost impossible to see. Apparently they made it more difficult to check timing on these years. That’s what I read anyway.

Checked for vacuum leaks with carb cleaner and a smoke tester. Nothing!

 

[Orangepeel]

Is it humid where you’re at? Have you tried spraying ignition components down with water while it’s running?

Yep no change