Re-post..truck starts well, then misfires badly... (1 Viewer)

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My old post said it goes to 2000rpm's and then dies, but that's not exactly correct. It seems to start everyday after sitting overnight or until it cools off and runs well for 2-3 minutes before starting to misfire, hesitate and generally run like crap. I've gone over every vacuum hose, checked the air cleaner intake from MAF, fuel pressure etc. Still the same thing, after a week. I replaced the PCV valve, took out the brand new plugs(black from misfires), checked all electrical connections. Fuel filter's next, but I doubt it. I get no codes, no check engine light, nothing. My exhaust system leaks at the O2 sensors, but that I can't believe that would be it.
I'm thinking now it's gotta be either the MAF(remember no codes tho'), the Ignition Module or Emissions/EGR, since the truck runs fine until it warms up. Kinda feels like once it starts emitting warm exhaust, the problem begins? I don't know.... How does one check the EGR and the Ignition Module?

Does anyone have any other suggestions. I'm running out of options and patience, as she was running like a top beforehand, and I miss her!

Thanks guys. :confused:

Nick
 
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Don't know age of fuel pump. Fuel filter maybe 6-7 years and 6-8000 miles.
Re: the O2 sensors; I pressure washed the vehicle, and they certainly could've gotten wet...ya think they're what's causing the problem? Any way to test?
 
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Coil readings

Read the coil ohms just now...Primary Coil Resistance supposed to be .52-.64 Cold. Mine jumps around like a Mexican jumping bean...30, 12, .5, 16, all over the place.

Secondary Coil Resistance is perfect; 11.5-15.5...mine is 12.0.

Gotta be the coil, no? Would a bad coil produce the aforementioned symptons? I hate replacing things to find out the truck still mis-behaves!!!
 
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The coil reading should be steady. You did unhook the wires?

Anyway, It must be something thats on when cold, and should be off once warm. In your case, that devise is staying on. Check all of the sensors on the thermostat housing. And look at the FSM in the trouble shooting section.
 
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Cold start injector is on when cold and then shuts after after the truck warms up. It enrichens the mixture when starting, much like a choke on a carb'd engine. Perhaps the sensor or switch that controls the cold start injector is not working properly.
 
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Replaced coil...not fixed.

I ran out and got a new coil. Tested it beforehand and was getting constant readings, not like the old one. Car started, but began misfiring shortly thereafter. 1800-2200 rpms seems to be the trouble spot. By fooling with the throttle, I could get her up to 3000 and hold her there, but letting go she stalls thereafter.

Guess I'llnstall the new fuel filter. Might as well.

Believe me, I've been through the FSM troubleshooting section.

Where is the cold start injector and switch?
I'll will defintiely check out the thermostat sensors, somehow.

Rebuilding her, one part at a time!
 

tag3

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My 60 would do about the same, 2000rpm stumble, stumble. Ended up being the egr valve had a tear in the diaphragm. Replaced and no more stumble.
 
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Thanks Tag

I suspect the EGR valve as well. I can't figure how to get that thing off though. All the FSM says to do is remove it and replace it with a new gasket...advice?
 
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Cold start injector and EGR

Cold start injector tests fine electrically..3.5 ohms(FSM 2-4 ohms)

How does one test the Thermostat snesors on the housing? No values in FSM.

How does one test the EGR? I suspect TAG may be correct, but I don't want to drop $175 to find out that's not what's wrong? The FSM says connect it to the Intake to see if the engine stumbles or stalls, but it's already stumbling!

What about the O2 sensors? Mike Hanson suggests those. Could they be affecting the misfiring? They seem a pain to test.

Thanks guys. This is quite a dilemna. Driving me crazy.

Nick
 
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Found an old post...maybe?

I found this post from 2008...maybe?

https://forum.ih8mud.com/60-series-wagons/204395-fj62-hesitates-no-power-rough-idles-times-6.html

He had the exact same symptoms, and went through hell diagnosing the problem...kinda like what I'm going through. After reading it, I drained my tank almost hoping it had water in it, added new gas, and got the same result.

So next up is dropping the tank and changing the fuel pump. If that doesn't work, I don't know what to do next. That won't be for weeks because I'm going away....argh...
 

tag3

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Rev the engine till stumbles, spray some carb cleaner around egr and see if rpms increase. Warning carb cleaner is flammable.
 
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This just occurred to me. You say that your problem is after the truck warms for a few mins. Check the accordion intake hose going to the throttle body.

Possible scenario: Cold start injector operasting for a few mins while engine is cold to enrichen mixture. Cold start injector turns off, mixture leans, unmetered air enters intake and makes mixture even more lean which in turn at idle causes a stall. At higher RPM, stumble is not as evident, but truck still doesn't run perfect.

Similar to vac/intake leak on a 60 series where the truck will run off idle or with the mixture richened with the choke engaged, but will stall out at normal idle mixture (with leak).

Does this make any sense?
 
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Just re-read your first post.

Your plugs are black, which would indicate fouling caused by an over-rich mixture.

If you have exhaust leaks near your O2 sensors, it could be reading lean and the computer could be trying to richen the mixture too much.
 
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Been over the accordion hoses, had it off and inspected today, it's fine.
Checked cold start injector switch, also ok. Definitely a hole or split in the weld at the O2 sensor, was why I was getting new exhaust.
But that post I found back in 2008, in a few posts back, hits the nail on the head for my problem. Couldn't a sporadic or faulty pump create the lean condition as well/misfiring?

I sure don't WANT to drop the tank, but after reading that old post, I think it's the way to go. Can't do it for a few weeks though, I'm going on vacation.

Thanks
 
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Aren't your plugs black, as in fouled by too much fuel?

Dropping the tank on a whim is going to be a big pain in the ass.

You said your truck exhibits the same symptoms right after warming up. I would suggest going through the EFI chapter in the FSM step by step and reading what all the components do under what conditions/temps, how to test them, etc.

I'd almost bet on a coolant temperature sensor or coolant temperature switch rather than a sporadic fuel pump especially if it runs better and doesn't stall, buck, or hesistate too much at higher load.
 
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Very good. Of course you're right about dropping the tank. I've been through the EFI chapter, tested what I could test, and am left with spraying Carb cleaner around the EGR later today under misfire to see if it sucks it in and improves the misfire...carefully.

I'm with you on the coolant temp sensor and/or switch, but am unsure how to test...and yes, it does seem to hold farily well at 3000 rpms after warm up, and even idle; 2000 rpm's is the culprit. I don't take it out because I'm afraid of failure, so I'm doing this all in my garage and driveway.

After running, it always smells really rich in there. This sucks, but you're helping...thanks! It's so frustrating.

Nick
 

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