4.0L with OHV and random misfires on all cylinders

[Sndsational]

So I have been posting on the page now trying to figure out why truck runs like crap. After a system diagnostic done today, here is the result:

random cylinder misfires on all cylinders.
found that the MAF is fine
new idle air control valve
intake had been smoked and no leaks found
backpressure test shows that cat's are fine
no CEL coming on
new coil pack, wires, plugs

I really need some input here. Can anyone throw ideas on what may be causing these misfires that is leading to poor performance? I have been chasing issues in this truck for some time and just cannot get it to be "right"

Additionally, there have been other things done, but too much to get into right now. please help!!


Thank you all!

 

[Vargas]

Is the wire order correct at the coil pack? 6/5 swap is easily overlooked.

How steady is your temperature gauge? Could misfire be the result of localized hotspots due to air trapped in cooling passages?

Is it driveable? How is the mileage?

Have you checked fuel pressure?

 

[Sndsational]

Thank you for the reply...

I looked at my wires...everything seemed ok, but I will double check. As far as the temperature, it holds steady right in the middle of the gauge...no fluctuation.

Truck is a daily driver...mileage is about 230 miles per tankful...averages about 14-15mpg.

One thing that the mechanic told me was that it could be the valves. He said that if the seals are all rotted and not seating properly that this could cause an issue. Any thoughts?

I did not check my fuel pressure yet. Do not know how...HELP?

Thanks

 

[Vargas]

How about a little more background on the misfire?

Did it develop suddenly, or over a period of time? How long?

Describe the symptoms - Backfire? Stumble/cough? Lack of power? Hesitation? Bucking?

You described it as random. How often does it occur? Does it matter if the engine is cold or warm?

Of those new parts, which ones have been installed AFTER the problem started. Did they have any impact better or worse?


Many auto part stores that rent tools will have a fuel pressure test kit. It will have a whole slew of various adapter fittings. The only pressure reading we care about is at the fuel injector rail. A good reading at the rail means everything in the pump/filter/regulator equation is working properly.

 

[Sndsational]

The truck seems to have developed the problem over the course of time. The parts that were replaced were to try and solve the problem, but at best made a "slight" improvement. The truck still seems to have a rough idle.

As far as the random misfire, that is what I was told, but it seems that the truck cannot get out of it's own way at times. It is like a lack of power. Now the interesting part. It seems as though at times the truck has power and other times not??? I think maybe it could run a little better on the colder days, but not entirely sure?!?!?!

When I am driving, the truck shifts through the gears and at times you can barely feel them...other times, they are firm almost bucking shifts. The transmission, however, is new and the fluid and such is fine (clear and non-burnt). It seems something else is affecting how that is performing, not an actual tranny problem.

I know that when I "get on it", the truck seems to struggle...then the tranny upshifts/revs up (again seeming to struggle to get to speed) and then downshift and cruises. it is not like it is easy for it to do.

I wish I could explain it better.

Thank you for the help, kep it coming.

 

[Vargas]

How long have you had the Ex?

 

[Sndsational]

Maybe around 5 years, give or take. But upkeep has been pretty good and I really do not beat on it. Hope that helps

 

[Vargas]

When did you last change the fuel filter?

 

[Sndsational]

Within the last year

 

[hoss_hanna]

really sounds like an intake gasket problem, i know u had it "smoked" but try an old shade tree trick on it, get a can of spray carb cleaner and start the truck, let it idle a min then start spraying short bursts around all the intake gasket areas, if the truck reves up during this then u can find the air leak. the "random miss" code tells u alot when a miss happens the o2 in that cylinder doesn't get consumed so the o2 sensor reads that there is o2 in the exhaust so it thinks u r running lean and applys more fuel, can really make the engin run funny ie sluggish and surging

 

[joe doe]

check the timing .if plugs,wires,coil pack have been changed and it still runs like that without throwing codes i would check the timing .
timing chain could be going bad .

a leaking intake would throw codes
a misfire would throw codes
low fuel pressure would throw a code

check engine lite on?

ps -i have a 2000 4.0 ohv and i been down alot of roads with it mechanically.misfire on all cyl?sure sounds like a timing chain .enough slack to slip 1 tooth would do it .


are you sure the bulb in the cel lite is working?a misfire in all cyl would surely set the cel off.

 

[Sndsational]

Already did the carb cleaner trick, I thought the same thing that it could have been leaking again. Actually did it before intake was smoked and found nothing.

Timing, to my knowledge, has not been checked. Can try that. CEL light was working and has thrown other codes recently while this problem has been happening.

All great answers guys, please keep 'em coming!

Thanks

 

[joe doe]

what codes did it throw exactly?that will help alot.
code numbers we are looking for ....

 

[2000StreetRod]

Random misfires

Your PCM should detect and report random misfires due to ignition problems and you have replaced coil pack, wires, and plugs.

You stated that your MAF sensor is fine. I wonder how it was tested. The PCM has difficulty detecting a bad MAF sensor.

If you have been negligent in replacing your fuel filter every 30,000 miles then your fuel pump could be failing. I agree with Vargas that you should perform a fuel pressure test. The PCM has no way to monitor fuel pressure which should be 60 to 65 psi when ignition is turned on or any time the engine is running. See My Helpful Thread Fuel pressure test procedure

I also suggest that you test your throttle position sensor. A "noisy" but within range TPS will go undetected by the PCM can create havoc with the engine. See My Helpful Thread TPS Test Procedure

Did you "read" the old spark plugs when you replaced them? The plugs provide visibility not available to the PCM.

Other things to consider are a malfunctioning crankshaft position sensor and camshaft position sensor.

I doubt that your timing chain has slipped. The OHV V6 engine timing chain rarely slips due to the ratchet/hydraulic type chain tensioner used.

 

[hoss_hanna]

i have to aggree with 2000streetrod it is a rare for the 4.0 to "jump time" id check the crankshaft position sensor and camshaft position sensor if u are very shure there is no air getting in after the MAS

 

[Sndsational]

Lot of great info guys!!! Keep it coming. The TPS had been replaced, but that does not mean that it has not failed. I will check it. I also replaced the crank/cam position sensor (whichever one is prone to the "chirping" noise).

As of late there have been no codes, but I had gotten lean codes when the intake was bad. Therefore I am assuming the light is still ok.

When you said "read" the plugs, what did you mean? Never heard of that.

Again, thank you all for the GREAT info...this is giving me a good starting point.

Thanks

 

[2000StreetRod]

"read the plugs"

Lot of great info guys!!! Keep it coming. The TPS had been replaced, but that does not mean that it has not failed. I will check it. I also replaced the crank/cam position sensor (whichever one is prone to the "chirping" noise). . . . When you said "read" the plugs, what did you mean? Never heard of that.
. . . Thanks

Did the electrodes and insulators on the plugs all look similar? Did one or more plugs look like the mixture was lean? Did one or more plugs look wet or carbon fouled?

The camshaft and crankshaft position sensors are separate. The crankshaft position sensor is next to the balancer and is exposed to the elements. The camshaft position sensor is on the top of the engine toward the rear. If either one malfunctions the engine can lose power.

 

[Vargas]

Therefore I am assuming the light is still ok.

Don't. Verify that it works. Light should illuminate during lamp check (KOEO) before starting engine. If it is not working, there may be "hidden" codes.

 

[Sndsational]

Ok, so here is the update....

CEL is working, comes on at startup. Changed the crankshaft position sensor (only $15.00) and at the very best, it only helped a little...if at all.

Next step is the fuel pressure check. I think I may for the giggles of it change my fuel filter too, as it had been changed recently, but before that it had been a Loooooooonnnnnggggg time!

What about an exhaust leak? could that cause any performance issues? Also, not really sure but I think I may have had a hesitation today when I gave it gas?!?!?

I am at a loss, so continued help would be great.


Thank you

 

[hoss_hanna]

an exhaust leak before the o2 sensor may cause some issues...