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3.5 mystery misfire

21K views 95 replies 12 participants last post by  Ruggels 
#1 ·
3.5 ES car will misfire or stumble @ 2000+rpm the problem is worse at exactly 2k rpm where it will miss/stumble repeatedly, or at least every one second..... at above 2k rpm the miss/stumble will happen about every 5-10 sec.... when the hood is popped and listening to the problem you can hear a slight hiss type noise (best i can describe it) coming from cylinder 3 or 5 area but only when the stumble happens.... about once a trip the cruise light will flash only when the stumble happens (usually on freeway at around 2.3k).... also while at idle a small clank can be heard from the #3 or #5 cylinder right where the valves are (its very quite and can only be heard if you really listen or put ear close) my dad said it was a lifter or valve sticking and eaither a oil change or oil additives will fix that?..... tach (means rpm gage right? :smileyvault-newhere) will vary on the misfire its hard to explain, while in park, about 70% of the time the missfire will drop rpm only about 100-200 but other times the rpm will drop 300-600 rpm.

things already tried

1)fixed pinched fuel line
2)replaced fuel filter
3)new crank sensor (ended up new sensor was bad and the original worked better have not tried a new "working" sensor)
4)replaced drive belts/water pump/timing belt/ TB tensioner (more just needed to be done then assumed the problem)
5)replaced faulty coil pack (read 16.4 ohms with new pack reading 12)
6)plugs were replaced about 100 miles or less before the problem started
7) sprayed carb cleaner around manifold gaskets and intake hoses with no vaccum leak detected
8)just tested the wire ohms today and they dont seem right to me they are as follows
#1-12.6
#2-20.7
#3-18.2
#4-22.8
#5-20.4
#6-21.9
seems even worse when they are lined up next to each other like that :baseballbat:

is it possible the lifter/valve sticking as mentioned before could be causing the misfire? or possibly the timing is slightly off?(i would assume it wouldnt only effect the #3 or #5 lifter but instead the whole side of the block thats off) but just your opinions would be appriciated

the engine is throwing NO CODES, no MIL or key dance codes as far as the car is concerned nothing is wrong besides the rare cruise light flash.

i feel my next course of action will likely be new wires depending if they are good or not, then, if nothing else look into compression/vacuum test, and getting the car plugged into a scan tool.

only good thing from all this everything i have replaced so far needed it :hit1:
 
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#4 ·
thats one of the things i was thinking when i was spraying it because i noticed even after taking off the black metal cover on the penilem or w/e its called, i still couldnt get much access to spray the lower gasket


can anyone verify those plug wire resistances??

also is their a way i could test the cam sensor with my multimeter instead of throwing 50$ into a maybe solution
 
#5 ·
When were the spark plug wires last replaced? They can easily wear out at 30K miles. Measuring resistance is not sufficient. A wire can become more inductive with wear.The connection from the wire to the coil pack can also easily corrode. When the spark plugs were replaced, did you use Champion coppers? The electronic engine control system is designed to work best with those plugs. If I were you, I'd first spring for a new set of wires. Use dielectric grease at the ends to block moisture.
 
#6 · (Edited)
champion coppers, yes, i checked the connections on the inside of each end of every wire when i tested em and no corrosion was visible, no idea when last replaced, they were all lacking grease but i doubt that would cause an issue??

what is the resistance range per foot of wire... ive herd 3000-5000/ft and 2000-4000/ft???
 
#7 ·
IMO ohm readings on your wires are high, you should read like 4-6K per foot, get some new wires or take your meter to the parts store and ohm a new wire.
 
#8 ·
BTW - I had the plug boot end on one of these cars that was arching badly to the tube in the valve cover and causing a misfire and it actually didn't ohm badly.
 
#9 ·
i did the plug wires after reading the ohms of the new wires at the store, still no fix and ordered the manifold gasket when i got the wires, any other gaskets i should replace while im inside,,, and i cant seem to find much in the forums about the manifold anyone have any advice?
 
#10 ·
Be careful removing the bolts near the thermostat housing, they tend to seize up. If the bolt looks rough replace it. While you are in there I would replace the injector o rings while you can get to them, its cheap and easy. If your valve covers are leaking you should do those now as well.
 
#12 · (Edited)
finally have the day off tomorrow and the gaskets came in so i started as soon as i got home from work i got the entire manifold taken off and gunna call it a night at that, just a few questions before proceeding tomorrow....

dispite my best efforts (prob coulda been better) it would seem some debris has found its way into one or 2 of the valve cylinders its minimal but i still want to get it... how much would a little debis hurt?.... how hard is it to get to the actual valves, from what i can see if i remove the valve covers i still wouldnt be able to get to were i need?

should i use a gasket sealant? ive heard its not required but better safe then have to pull it all back out right?

since im this far into the engine already i figure might as well do the injector o-rings, PCV valve, valve cover gaskets,... would it help to replace the break booster valve as well?

and throttle body was surprisingly clean the rest however.... is not ive sprayed much down with TB cleaner to sit over night but i dnt think thatll do the trick its really caked on any advice on cleaning?

edit: oh yea and every gasket ive seen so far has been bad enough to crumble very very easily
 
#13 ·
Since you're dealing with a 1st gen 3.5L, I don't think I'd mess with the injector O-rings unless you already have evidence of leakage. The injectors are seated in a rail that is removed by three bolts. If you remove these rails, you won't have to mess with the injectors directly. Just lift all three per rail at a time. There is a gasket below the rail that is made out of the same material the intake gasket is made of so, you'll probably find these are crumbling as well.

The reason I mention leaving the injectors in is because removing them from their rails is a job that requires a bit of finesse to prevent fracturing the rail they are set into. If you do end up pulling them out, there are a couple more O-rings at the ends of the fuel rail to deal with as well.

One last bit... Don't try pulling the injectors from their electrical connector! Instead, find a chunk of hard wood or plastic and carefully push them out from the pintle end.
 
#15 · (Edited)
Yes, there was a recall. Trying to remember now was it #790? I will look and see what the actual number is.

If you can get the recall kit, it has all the gaskets and O-rings for the rails. It would probably have to be special ordered for you as most dealers won't stock a recall part from so long ago.

EDIT:

Yep, it's #790

It also dealt with gluing on reinforcement strips to the fuel rails to prevent them from busting. You'll likely find these are already stuck to your rails.

The kit is part number: CAXJ7901
 
#17 · (Edited)
after finishing it all (decided to pass on injectors) i have a no start with code 54 cam sensor not sure weather its the wires or the sensor but is their a way to test each? i dont want to buy a non refundable sensor just for the problem to be in the wires

also the MTV vacuum hose broke when trying to get it back into place so going to get a new one of those as well,,,, i doubt this would cause the no start and code though

i also noticed what looked to be a vacuum line that comes from a wireing harness in the center rear of the engine that feeds toward the driver shock tower then stops as an open line what is this? i cannot find a spot that this would go and their are no connecters on it

she really wants to start, id almost say it does, but its very clanky and dies right away
 
#18 · (Edited)
after getting the MTV hose i was able to get her started and the code 54 went away but the original problem of the misfire is still in play.

i cant remember if i said how i have a valve or lifter "sticking", but when she was unable to start last night the valve/lifter was clanking real loud and then when i got her started it continued for a few moments before quieting down to the same level previously. i assume that this is because of a lack of oil and it took a few moments for the pump to circulate it to the lifters

what are the chances that lifter is causing my miss?
 
#19 ·
found where that line went... i was looking all around the engine for somewhere to connect when it ended up being the cruise control... was also surprised to find that the cruise control is controlled by oil because when i was driving and the cruise didnt work (because of disconnected line) i found a rather large oil leak at next stop and began to panic, but after connecting the hose back on the leak went away and cruise came back.

i think im going to try another crank sensor and go OEM since my last i took back after putting it in and it started a ticking comming form the trans.... i also noticed that on first startup after it sat overnight the trans will give the same ticking but will go away at warm op temp, any other suggestions?
 
#20 ·
Cruise Control is operated by vacuum. If you had an oil leak at that point...maybe a PCV issue? Where Oil in the upper plenum was getting pulled back to the Cruise Control Servo?
 
#22 · (Edited)
UPDATE



more things done without any effect,

got the wire/coils still nothing....
did the intake gaskets, added a new PCV valve, did a few other things while down their an still nothing...
got new cam and crank from the dealership and man was i glad i spent that $140 for nothing...
also redid the timing belt with no change...

the only thing that has made the slightest difference is the crank sensor helped while above 2k but the miss is still very prominent.

idk what to do now im kinda out of ideas any help would be really appreciated... and before someone says injectors, idk how on earth that would cause the cruise light to flash
 
#24 ·
i have yet to do a compression test half cuz im scared to see, half because i didnt think that that could cause my cruise light to flash, but seeing as im out of ideas that seems to be next... if it does end up being compression issue then am i looking at a rebuild?
 
#25 ·
Yes, you'd be looking at a rebuild.

As for your blinking light - check the pins in the connector for the cam sensor... Make sure they are fully seated in the plug, and that the pins are clean on the sensor. Also, make sure that the pins are actually being grabbed tight by the individual connectors in the plug. Is the catch clip intact on that sensor?
 
#26 · (Edited)
ok so compression test reads as follows (the diagram is front to back since i am not 100% sure thats were each wire goes my new ones dont have the little luxury of my old saying on the wire what is what)
(5?)x-165 (6?)x-165
(3?)x-145 (4?)x-155
(1?)x-150 (2?)x-165

the pins on the connecter were tight i didnt want to pull too hard but giving a nice tug wouldnt free any of them..... if i think i know what u mean by the catch clip then no its been broken off, but the plug does not move after you let go of it i watched closely for that after i first broke it off a while ago

any ideas next? id assume the comp is ok since anything ive seen bad is more like under 100's, ive redone the timing 2 times and didnt change it for better or worse but my dad really thinks thats it, what are the chances that it would start and run fine but then come into problem if the timing was slightly off
 
#28 ·
yea i was glad to see good results on compression, the local pick' n' pull had a 50% off everything sale and a saw a few good 3.5s so if i had to get one that woulda been the time.

guess its time to start deciding weather to buy my own scanner or take it too the shop, as a 94 i have a OBD1?, do they make a OBD1/OBD2 scanner? i wouldnt want to buy a OBD1 just to never use it on another car.
 
#29 ·
It is OBD1.... But I don't know what a scanner is going to get you...

I think it is time to go over the vat with a fine tooth comb... Check every electrical connector - ideally one at a time, then test run. Unplug each one, look at it, plug it back in then try again with the next one. Also, go over each wire harness one at a time, looking for damage...

The only other thing that come to mind is that there is a thread here on the board about how all the engine sensors run on the same 5 volt line, and an intake air temp sensor can make the voltage bad for something else on the line, giving you fits... I can't search right now, but see if you can find it.

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