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99 4.0 ohv problems :-(

Lean mixture causing misfire

I suspect that the lean condition is causing your misfire. Especially if the DTCs indicate multiple or random misfiring cylinders. You should correct the lean condition before pursuing the misfire condition. I suggest that you perform the Lean condition procedure
and review the Engine misfire procedure that I've just started generating.
 



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$50 on the fuel pump! I just had this problem till my X would bog out under half gas pedal then it died in the middle of the busy city. good times.

Oh and my codes read lean, both banks.
 






or even the egr valve =o but lean code is usually just pcv
 






just tested the fuel pressure.....65psi at idle. it would drop about 3 psi when i would open the throttle hard but that seems pretty normal. i wish i could check it while driving but im pretty sure there's nothing wrong with the pump now. 65 is at the top of the "acceptable range" giving in my repair guide.

i guess i'll check the pcv and egr next.

is there any way to test the fuel injectors? or can they be taken out easily?
 






Fuel pressure good

Those readings indicate suitable fuel pressure but remember there is very little load on the engine when in Park. How long since you replaced your fuel filter?

You can test the fuel injectors electrically with a noid light but not the flow. It's unlikely both bank's injectors would go bad at the same time unless there were deposits in the fuel that clogged the injectors.

Frankly, I can't think why a PCV valve could cause a lean condition. The air flowing into the crankcase and out of the PCV valve into the intake manifold is metered air. If the valve is stuck open there is no more airflow than normal. If the valve is stuck closed there is less airflow than normal which results in a slightly richer mixture. If you plugged the port on the main intake tube that connects via a hose to the valve cover port and installed a breather on the valve cover port then there would be unmetered air entering the system.

A lean condition results from less fuel than the PCM requests for metered air or air entering the system that is not metered or a combination of the two.

Did you test the MAF sensor and TPS?

Does the engine flare when cold started? Do you have the SOHC? If so, I suspect that your intake manifold gaskets are leaking but you should eliminate other possibilities first.
 






Those readings indicate suitable fuel pressure but remember there is very little load on the engine when in Park. How long since you replaced your fuel filter?

You can test the fuel injectors electrically with a noid light but not the flow. It's unlikely both bank's injectors would go bad at the same time unless there were deposits in the fuel that clogged the injectors.

Frankly, I can't think why a PCV valve could cause a lean condition. The air flowing into the crankcase and out of the PCV valve into the intake manifold is metered air. If the valve is stuck open there is no more airflow than normal. If the valve is stuck closed there is less airflow than normal which results in a slightly richer mixture. If you plugged the port on the main intake tube that connects via a hose to the valve cover port and installed a breather on the valve cover port then there would be unmetered air entering the system.

A lean condition results from less fuel than the PCM requests for metered air or air entering the system that is not metered or a combination of the two.

Did you test the MAF sensor and TPS?

Does the engine flare when cold started? Do you have the SOHC? If so, I suspect that your intake manifold gaskets are leaking but you should eliminate other possibilities first.

Intake gaskets were what I initially suspected, but then I re-read and saw "99 4.0 OHV"... doh
 






yea its ohv.....ive listened for vac leaks around the manifold anyways, didnt seem to be one. truth be told im pretty confused at the moment. i agree with what 2000streetrod said that i only got a FP reading under no load, but i feel like if its showing the perfect factory reading then i can somewhat give it the benefit of the doubt and assume its working properly.

i also agree that i do not believe either the egr or the pcv could be causing this issue.

i dont think enough air could be coming into the system unmetered that the problem shows under load and at a high degree of throttle. a vac leak just doesnt fit the bill. its either an ignition/timing problem or a fuel shortage. on that note, is there not a code that will throw up the CEL if the MAF is suspected to be faulty? or is it possible that because it is functioning, just not working 100% that it does not recognise the MAF as the culprit and it can only show me the multiple bank lean codes?

one more thing, if it is an ignition/timing problem wouldnt it throw up misfire codes?

its hard to tell if the misfire is due to a lack of ignition or a lack of fuel. if you go by what the computer says it fuel......maybe i will go get some MAF cleaner.......

i almost forgot.....the TPS. the main purpose of the TPS is to account for rapid throttle changes right? well i can change throttle positions as fast as i want and thats just fine. i just cant go past a certain amount of load/throttle. once i ask for too much torque it starts to stumble. and i wouldnt say it feels like a complete misfire, it feels like a very weak fire.
 






fuel filter?

You never mentioned how long since you changed the fuel filter!

I agree that an intake leak should have the most effect when the vacuum is strong (idle). Do you have your own code reader? If so, you can determine if the lean DTCs get set at idle.

A stuck open EGR valve should set a DTC and would make the idle rough.

Is the intake system stock?

Did you test the TPS and MAF sensor with a voltmeter?
 






fuel filter is new. i have a k&n panel filter, removed that restricter from the airbox. i have a throttle body spacer which i would like to remove bc i think it is rubbish, and a highflow muffler.

it idles fine most of the time, but it has on occasion had a period where is runs rough for a minute during warmup. it will be running fine then it will start to bog down and struggle for a minute then usually it will go back to normal and be fine. or if when it starts to bog i give it some gas and let it rev up a little it will resettle back to normal. that doesnt happen very often. very rarely really.
 












I suggest that you clean the MAF sensor with MAF sensor cleaner. If the air filter is well oiled it will contaminate the MAF sensor. Test the MAF sensor and TPS with a voltmeter. Otherwise, I wish you luck.

He got a new one from NAPA but I'm still skeptical. It would be great to know the "BARO" parameter or even voltages so the MAF can be taken off the list or replaced.

A scan tool can also read EGR, and determine if there is any flow at idle. There are rare instances where a bad DPFE can cause those codes, but its just a guess.

Also, an oiled K&N filter is not MAF friendly.
 


















thanks that was a good article
 






DPFE "usually" gives codes?

Curious as to whether this would malfunction without throwing a code....

?
 






i think maybe the MAF has gone bad. it used to be when the engine was running if i would unplug the MAF the idle would get pretty rough. right now if i unplug the MAF it doesnt change all that much, it seems to change more when i plug it back in, the idle gets kinda crappy for a few seconds then smoothes back out.
 






DPFE "usually" gives codes?

Curious as to whether this would malfunction without throwing a code....

?

Yes, its possible. It may not reach a certain threshold to give a code, but cause driveablity symptoms or set other codes. It can also work intermittently in a way that doesn't satisfy the criteria for a hard fault. The MAF is the same story, unless its close to death a code won't be set.

Remember that OBDII allows for a fudge-factor of I believe 50% over the limit before triggering the light. It can also compensate by using more gas, IAC cycles, etc. This also helps compensate for aging components. You won't get a code but the car won't run optimally either. The PCM software (written in C) is available and gives real insight into "the womans mind" so to speak.

That is why live scanner gives REAL clues into what is going on, and you can see the numbers yourself instead of relying on a computer to set codes.
 






what is a good live scanner is can buy/where can i buy it
 






ok,ready.......
those codes are thrown when the upper plenum gaskets are leaking .over time these rubber type gaskets get compressed to the point where they wont seal anymore .then the code gets thrown.

this is the gasket sets right under the "upper plenum"no need to remove the intake just the upper plenum .
under there you will see 3 sets of gaskets ......they are rubber or plastic looking and theres a set for each intake runner so theres 3 in the set .

buy this gasket at the dealer .its affordable .replace those and your cel will go out and your engine will return to normal .

i had to do this last year on my 2000 ex sport with 4.0 ohv engine .

i am surprized more folks didnt chime in and know this answer .

next time do a search on here by inputting those codes into the search window and you will find your answers faster .

this is the fix,dont mess with the other stuff.my ex threw the same codes and it went away once those gaskets were replaced and has never returned.
 



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Good advice!

I suspect that the lean condition is causing your misfire. Especially if the DTCs indicate multiple or random misfiring cylinders. You should correct the lean condition before pursuing the misfire condition. I suggest that you perform the Lean condition procedure
and review the Engine misfire procedure that I've just started generating.

joe doe said:
. . .
i had to do this last year on my 2000 ex sport with 4.0 ohv engine .

i am surprized more folks didnt chime in and know this answer ..
 






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