possible belt slippage?

as i was heading to my brothers house, he was driving next to me in his dakota. decided to try and race me which is always funny. when i gave it some gas (about 3/4 or so) it started to buck pop and backfire. let off. plugged scanner in. no codes. did another pull watching the scanner and the fuel trims were bouncing around pretty bad as it started to buck. so did one more pull and watched the boost gauge (in a bad spot to watch while driving) and as it climbed to about 7, it would start to buck and bounce between 3-7. only thing i could think of was belt was slipping. im replacing the belt later today but is there something else that would cause this? and not throw a code?

How many miles are on your car, and when did you last replace your ignition wires?

121k replaced wires 6k and plugs 2k ago

rpms werent really bouncing around. they were still slowly climbing.

If you can log data, and you see it loosing boost before everything else, it could be the belt, but you would loose boost anyway almost instantaneously, so I would suspect you have another issue and the loss of boost is the immediate result. Normally, a slipping belt would show a sharp loss of power, not much else.

Did this problem start all-of-a-sudden? Does it show any KR when it happens?

no knock when i was scanning. cant data log. dont have aldl cable yet. wasnt sure if the belt was slipping then grabbing again. and ya that was the first time it has happened. scared me pretty bad. haven't put the foot down to see if it happens again till i change the belt.


one thing i was thinking was. i posted earlier about it. every once in awhile i get 2 codes saying spark advance isnt toggling. i just turn the car off and back on. goes away. dont know if that could effect me even tho the ses light wasnt on this time?

Has the belt ever been changed that you know of? If not, at 121k it's time.

If that's not it, it could be a failing coil pack or a fuel delivery problem (injector, filter, pump). Keep us posted when you figure it out.

the belt was changed around the 70k mile mark the previous owner said. so i just changed it. 1st holds 7. 2nd spiked 7 instantly dropped to 5 then 3 and held 2 thru 3rd gear. i changed the plugs every oil change and the wires every 3 oil changes. will be checking the plugs when the car cools down. how do i check the coil packs? and how will that affect the boost? i have gone over my vac lines and all are still secure and zip tied so i dont think boost leak..

Anything that effects the engine's operation will also affect boost, because the blower is directly driven by the engine. If you have a miss, lack of air, or lack of fuel, etc., it will result in reduced boost almost instantly. Unless you can verify engine RPM is still high when you loose the boost, it's hard to point fingers at the belt. It's possible, but it could also be just about anything else.

For the coil packs, I would buy one and swap it one at a time in place of the three. The problem will go away when you replace the failed one. Coils are hard to test with our engines, because there are two stages of spark: normal & in-boost (higher spark). It is very possible for a plug, wire, or coil to work fine in normal driving, but to act up when in boost.

i guess i forgot to mention the rpms were at 4500 at the 2-3psi. normal is 9. 2.5 pulley

Based on that, it sure seems like this is spark related. That's my opinion, but you'll need to inspect or swap the components to verify which is making the problem.

anything else i should check. could the spark toggling problem be related even if the ses light wasnt on? possible ignition module?

I don't know if the 95 records the misfires in the PCM that will happen with something going wrong in the ignition system.??/
But to check coils, you need to use an Ohmmeter and measure the primary resistance as well as secondary resistance.
I don't know what the readings should be, but I can look it up in the 1998 FSM if you want.
You will also want to clean the upper and lower surfaces of the Ignition Control Unit of any corrosion while you have the coils off.
Make sure you mark your spark plug wires with some tape and a pen before removing them to avoid hooking them up wrong after.
Two small diameter but long screws hold each coil pack down to the ICU. Remove them carefully and turn them over for access to the primary connections and measure resistance between the two male connections on each coil and record your numbers. To measure the secondary resistance you just need to measure the resistance between each tower in the coil pack itself (where the spark plug wires go) and record the results for comparison later.
After you have all 3 coils off make sure you clean the male connectors on the bottom of the coils and use a ScotchBrite pad (or fine sandpaper) to clean the top of the ICU.
Now lift the ICU off the steel mounting pad and clean the corrosion from the bottom of the ICU. You will want to loosen and remove the electrical harness from the front of the ICU before trying to lift and flip the ICU over as these wires can and do become brittle over time. I forget the size of the socket required but it is small metric, same as the coil bolts.
After cleaning all the surface rust off both upper and lower surfaces of the ICU you want to spread a thin even coat of Dielectric grease on the surfaces to help retard future corrosion and promote a good ground.
Speaking of ground there is a small diameter Black wire coming from the ICU than is bolted to the engine block.
Remove the nut securing it and inspect that wire for any fraying and corrosion as well. This ground wire is very important in the operation of the ignition system. If it is broken off or frayed in any way you will want to repair it and clean the connector.
This is a known area for corrosion and a problem spot that needs to be done for preventive measures as well as step #1 before replacing any coils or ignition wires.
Inspect everything in this area carefully and clean it up good and apply Dielectric grease to the surfaces as well as put some on the pins of the large electrical connector that you removed from the front of the ICU.
Put everything back together carefully and report back with the resistance measurements that you have taken of the coils primary and secondary circuits.

Quote :

But to check coils, you need to use an Ohmmeter and measure the primary resistance as well as secondary resistance.

Does this technique work for supercharged engines, which use a higher voltage when in boost? If so, how do you trick the coil into producing the hotter spark?

I ask because 95ParkAveUltra says his engine runs fine at idle and for normal driving, but has problems as soon as it builds boost.

EDIT: found this info here: http://www.underhoodservice.com/Article/40247/servicing_gms_3800_v6_engines.aspx

"If you test a coil with an ohmmeter, the test specs are 0.5 to 0.9 ohms for the primary terminals under the coil, and secondary resistance of 5,000 to 8,000 ohms at the high-voltage terminal."

Yes, it is just a "static" test that can sometimes reveal a problem.
If a coil is failing under load you may or may not be able to tell by a simple resistance check but it is a good first check.
This applies to any coil, regardless if it's a "two speed" coil or standard coil.

AA,
That's a good find with some very pertinent Tech info.

so last night pulled the coil packs off and cleaned it all up. not really dirty. didnt get the primary resistance just secondary. which was 5.8-5.9. on my way home did another pull just as i left and held 5psi 1st-3rd. on the way back held 9psi with no problem. same thing today. not sure if any of that fixed the problem but my brother just now mentioned that when we were scanning yesterday my injector pw at idle is 3.3ish and as i would get into it, it would jump to 0.0

i scanned it today and 3.3 at idle wot is 30-33.2ish. is my injector pw suppose to ever be 0.0? this is obd1 so not sure what im looking at. also my LT FT is at 159. normal is 130ish.

your fuel trims should be around 128-129 thats pretty much zero point for the obd1, not sure about your injector pw,...

ok... well been keeping an eye on the scanner past couple of days. seems fine really havent got into it much. first and second hold 9psi just fine. today second gear bounced around alil but 3rd blows. right when it shifts into 3rd boost drops to 2psi. (got beat by a damn mazda 3 tonight, ran from me in 3rd ) not sure what to even check next. will be changing wires this paycheck. could bypass valve be failing or something along those lines.

check vacuum lines and your bbv. Use a vacuum pump to actuate the bbv and make sure it holds.

ok so i changed the spark plug wires. no change. thinking dirty map. i am getting lean fuel trim code same as https://rivperformance.editboard.com/series-ii-engine-transmission-f4/code-p0171-lean-condition-solved-dirty-maf-sensor-t6354.htm

however i dont really know where the map is located and how to clean it. plz help

.. 95 has no MAP.

is your MAF clean?

dont think i have ever cleaned it. would that cause that code? my fuel trims are maxed out at 160ish right now, way lean at idle thru the rpm range. what are the two black sensors on the bottom of the throttle body?

didnt know the 95 didnt have one. funny cuz autozone lists replacement part for it haha

95ParkAveUltra wrote:

dont think i have ever cleaned it. would that cause that code? my fuel trims are maxed out at 160ish right now, way lean at idle thru the rpm range. what are the two black sensors on the bottom of the throttle body?

didnt know the 95 didnt have one. funny cuz autozone lists replacement part for it haha

I doubt it will fix the code, but its a free thing to do that might make a difference.

If you have checked out all the ignition stuff that was suggested in this thread, maybe the next step would be to look into fueling, since your trims seem to be all over. Maybe see if you can check rail pressure, and that your FPR is working. I know the fuel pressure regulator behaves differently under boost vs not boost. The lean trims can indicate a fuel problem. I'm guessing fuel filter, FPR, or pump. If it was just an injector you should be getting a misfire code.

Cheap things to throw at it are MAF cleaning(free), fuel filter. Maybe find a used FPR since they are not really cheap.

Pump would be last resort, or if the rail pressure test was low. I believe you should have at least 45-50 PSI with the vacuum line off the FPR.

The two black things under the TB should be you Idle Air Control, and Throttle Position Sensor.

i dont think the 95 stores misfire codes. when i scan and watch engine section 2, which contains misfire 1-6 and maf fail and pass. i get codes present: yes but doesnt say which one is failing. ive tried watching for misfires while driving but nothing comes up. just switches from codes present: no to yes. i will clean the maf and change the fuel filter tomorrow when i have a chance. will pick up a pressure gauge this weekend.

i do have a small vac leak somewhere but its been there since before the problem started. just cant seem to find it. so i dont think that is the problem unless it has gotten worse. doesnt sound like it tho. will also try to track it down this weekend.

I always assumed that the "codes present" indicator was a kind of global indicator and not specific to engine section 2. So if it was for instance throwing an EGR code, the "codes present" would always be yes till it was cleared. But I could be wrong.