94 rodeo v6 stuttering problems

[nickpapa]

im trying to help out my girlfriends parents with their 94 rodeo v6 auto.

it has been stuttering/misfiring bad lately. at times it will run fine but will stutter intermittantly.

so far i've replace the fuel filter, plugs, all vacuum lines, cleaned the egr valve, and sprayed carb cleaner by the IMG but the problems are still there. the wires look good but i think they are autozone brand and not sure if that could cause the issue. i've also noticed that the misfiring/stuttering mainly happens under load in drive but not in reverse. although it has stuttered/stalled a few times at a stop.

one thing i did notice is that the pcv valve grommet is ripped at the bottom area where it would site and seat into the valve cover. you can just pull it out with ease. would that cause the car to run like this?

not sure where to go from here so any help is greatly appreciated.

[srpope80]

I would check the wires and make sure it is not arcing even the tiniest little bit. I've seen this alot on all the older cars i've owned/worked on; best way to check is wait until it's dark ouside, and then go and start the car. The darker it is the better. If it's arcing you should see it pretty clearly.

-Scott

[nickpapa]

i will try it again when its dark, but i did spray water over the wires to see if there was arcing but didnt see any arcing or any change in engine idle.

i did notice that the wires were able to come apart or atleast a bit. i noticed it on one wire (going to sparkplug), and i pushed it back together. i didnt try and see if the others did the same but is that normal? i know some wires are rebuildable so i figured these might be as well.

also, as i said above, the pcv valve grommet was ripped at the bottom so it was very easy to just pull up and out. would this cause the problems im having?

[nickpapa]

ok so i just went out to see if the wires were arcing. nothing is arcing, i even sprayed water over the wires to see if there is any arcing and didnt see anything.

i also took the wires off the coil one by one with the car on to see if there is spark. there was spark except for cylinder 6 which had spark but it didnt seem as strong as the others. could that be the problem?

but i do notice that when in drive, it will stutter/misfire, yet in reverse, it doesnt at all??

[trooperbc]

the thing is, as you probably know or are finding out, your symptoms could be caused by just about anything from fuel system, to smog components, to ignition system, to engine mechanical, etc, etc.

Originally Posted by nickpapa

...i also took the wires off the coil one by one with the car on to see if there is spark. there was spark except for cylinder 6 which had spark but it didnt seem as strong as the others. could that be the problem?

could be, and it could be intermittent, especially under load, but i'd think just one cylinder acting a bit weak wouldn't cause the symptom as described.

but i do notice that when in drive, it will stutter/misfire, yet in reverse, it doesnt at all??

this sounds either coincidental, or perhaps a result of the different gearing giving a different affect.

also, as i said above, the pcv valve grommet was ripped at the bottom so it was very easy to just pull up and out. would this cause the problems im having?

again maybe. it ought to be tight, otherwise the leak will affect engine especially at idle. just seal it temp with some cloth and/or tape and see if that affects a change for you.

for no particular reason, i'm thinking egr system. when you cleaned it, did you get that thin little port that looks like a vacuum line to the backpressure transducer (BPT). make sure it's clean and fully clear.

and the plugs, what condition were they? and was there oil in the sparkplug tubes? and the ignition wire set, sounds a bit shoddy(?). definitely suggest a quality set like oem, and if you have oil in the tubes, get the kind that has larger diameter connectors with built in seal rings to seal the oil from shorting out the plugs.

is the stuttering limited to cold or warmed-up driving? any other indicators that might point to the O2 sensor?

finally, back to the ignition, it's possible a coil or more is going. they do go defective idividually, and i've had one short, arc, intermittent (almost) nonexistent at idle but underload a real and growing problem. was able to diagnose using the darkofnight trick and use of cheapo ignition short tester from bigboxstore. also used an inductive timing light to spot intermittent firing. each coil fires two cylinders, the #'s are marked on the coil terminals.

finally2, on the fuel front, check the fuel pressure regulator. one easy check is to pull the vacuum hose off, if there is fuel in there at that port, then the fuel pressure regulator needs replacing.

//bc

[nickpapa]

thank you very much for the reply trooperbc i appreciate it. here are some updates from today:

so i bought 3 new coils from autozone, swapped them in and nothing changed. luckily autozone let me return them.

i also changed the pcv valve and grommet as the old grommet was ripped, and nothing changed again.

you asked if the symptoms change when hot or cold and the answer is no they dont change. since you said that, i decided to pull the fuse for the o2 sensor and nothing changed again. not sure if that fuse controls all 4 o2 sensors but regardless nothing changed.

so since i live on a hill, i thought i'd try reversing up it a good amount to see if it will stutter/misfire and it did not. once i put it in drive (even going down hill) symptoms came right back.

also the valve cover gaskets are shot as there is oil on the wires. but the wires i have i think are the ones that seal to not allow oil (as trooperbc explained it). the wires on there now look like these


i also noticed that there is an occasional pop coming from the airbox (im almost positive its the airbox) while it is stuttering/misfiring.

as far as the egr valve, i took the one that is by the firewall which says egr on one side and vsv (could be wrong) on the other side. i just sprayed some carb cleaner into it and had some black stuff come out of it. not sure what you mean by transducer, this is the first time working on an isuzu so im not to sure on that term.

other than that, i had my brother put it in drive, hold the brake and give a little gas with the hood up so i can see if maybe there will be arcing that way but again i didnt see anything.

so atleast now we can narrow it down to not being

fuel filter
plugs
coils
pcv valve

i also spoke with my girlfriends father and he said when he bought the car it acted like this (but not as bad) brought it to a mechanic, he said he couldnt figure it out and gave it back to him and apparantly it drove fine for about 2 months until now.

[nickpapa]

any help is greatly appreciated guys!

[trooperbc]

Originally Posted by nickpapa

....
so since i live on a hill, i thought i'd try reversing up it a good amount to see if it will stutter/misfire and it did not. once i put it in drive (even going down hill) symptoms came right back.

well i guess you gotta go with what you're finding out, whether it makes a lot of sense or not. there really isn't anything engine or computer wise that cares whether you're going forward or reverse -- except the the trans inputs, of course. exactly where to go with that, i'm not sure from here, and at this hour.
first, i can assume no problems in N neutral?
if it were happening to me, and i noticed this forward/reverse thing, i'd guess i'd start looking at the trans mode switch system, which is what tells the electronics part of the transmission what gear you have selected. symptoms of a bad or problem switch are usually quite different, however.
how about, crawl under there and follow the wiring and see what you can [quote]see. the wires are right up there by the exhaust pipes and if they got dislodged maybe you've go a singed wire or two. the mode switch is on the outside of the trans, drivers side, where the the gear selector arms are.

that's where i'd start anyway.
mmmm... or

....brought it to a mechanic, he said he couldnt figure it out and gave it back to him and apparantly it drove fine for about 2 months until now.

i can't figure it out ! [see if that'll last 2 months....]

//bc

[nickpapa]

thanks for the reply trooperbc.

i have a little bit of an update from yesterday, i decided to take a spin in it right when i got home from work where i know the engine was cold. i started it and just started to drive. it hesitated a very tiny bit and all of a sudden it was driving normal with no problems at all. as soon as the engine warmed up a little here come the bucking/stuttering again. so i was thinking maybe o2 sensor? i am going to do the same thing when i get home today and see if it acts the same.

as far as the trans switch, i think that is a good idea but as you said the symptoms shouldn't be this way. so i think your right on how it might not be that because even while stuttering/bucking, i can feel the trans switching gears according to engine speed.

i will also try to reverse when the truck is fully warmed up and see if it does it.

maybe a bad ground? anybody have a diagram of where the grounds run?

again, thank you trooperbc for the help

[FL 3.2L]

It does sound sensor related. As soon as the engine gets warmed up it starts relying on several sensors to adjust the mixture. MAP sensor, O2 sensors, MAF, temp sensor, or something similar?

[FL 3.2L]

Has anybody put a scanner on it yet?
How about pulling plugs and checking their condition?

[nickpapa]

plugs are brand new. if you look a couple posts up i listed what was replaced. so far this is what has been replaced/looked at:

Plugs
Vacuum Lines
PCV Valve
Fuel Filter
All 3 Coils

i took it for another drive when i got home from work. when it was cold, it was drivable but still had a stutter here and there, once it warmed up, it was like pulling teeth to get the thing to move. but again when it was warmed up, i reverse all the way up my hill with not one stutter. freakin crazy. i dont get it

im going to replace the o2 sensor on saturday. hopefully that works but with this whole reverse thing it makes it so much more confusing.

also when in drive at idle it will stutter and want to stall, and if i put it in neutral it will idle perfect.

[FL 3.2L]

Read it all.

If you have a cylinder missing, it will foul a new plug and you can see it if you pull it.

[trooperbc]

Originally Posted by nickpapa

thanks for the reply trooperbc.

i have a little bit of an update from yesterday, i decided to take a spin in it right when i got home from work where i know the engine was cold. i started it and just started to drive. it hesitated a very tiny bit and all of a sudden it was driving normal with no problems at all. as soon as the engine warmed up a little here come the bucking/stuttering again. so i was thinking maybe o2 sensor? i am going to do the same thing when i get home today and see if it acts the same.

as far as the trans switch, i think that is a good idea but as you said the symptoms shouldn't be this way. so i think your right on how it might not be that because even while stuttering/bucking, i can feel the trans switching gears according to engine speed.

i will also try to reverse when the truck is fully warmed up and see if it does it.

maybe a bad ground? anybody have a diagram of where the grounds run?

again, thank you trooperbc for the help

okay, i've been thinking about this off and on today. here's my latest take:
iirc.....there have been a number of posts here or other sites where irratic and poor running ended up being traced to a messed up brake light. they fixed the brake light problem (might even have been a burnt out bulb; remember maybe a ground issue in another), they fixed that and fixed their driveability problems. i also believe trailer wiring connectors have also caused such problems. why? electricity does wondrous things and backs up places when it stymied, especially it seems with isuzu's.

now, in your case, maybe a clue is that all is well in reverse. that mode switch is really a triple-threat device 1. instructing the trans electronics on gear selection 2. neutral safety switch (will start only in N or D) AND THREE 3. the backup light switch. maybe, just maybe, when you are in reverse, the electrical circuit is completed back there, with the electrons going to the backup lights. without the backup lites working, the electricity is looking to complete its deviant circuit some other way, which ends up causing your problem(s).

anyway, that's my big idea. check the rear light assemblies, bulbs, contacts, etc, and trailer light wiring/plug, too.

//bc

[trooperbc]

....AND check out focus2win's neat little trick of pulling fuses....maybe there's something in it for you.....

http://www.automotiveforums.com/vbul...07#post5033807


//bc