Stalling after warming up

Hello everyone,
So i have a 95 Riv with a series 1 supercharged. I had it in the shop about 6 months ago to have supercharger rebuilt and the harmonic balancer replaced. After that visit car ran great until a couple months later. Then i would start the car up fine maybe sometimes having a rough idle, but ran fine. After driving for 15 minutes the car would begin to misfire, it would do it until I would pull over and shut the car off. Then I would turn the car back on and it would run fine for the next 15 minutes. I took the car in the shop and they said it was the lower intake gasket or plenum gasket. I got that fixed and the problem was gone. Now a couple months later again the problem came all back again with it misfiring or stalling after about 15 minutes of driving.

Like i said the car sometimes also starts pretty rough and not idling correctly, and sometimes it will even turn on the check egine light but it goes right off after a restart.

Any help would be appreciated because I am starting to grow sceptical of the shop I am taking it to.

did the shop replace the lower intake gasket, or just re-torque.

Replaced the gasket

Could also be a coil pack starting to go or ICM connection is bad. They would have pulled this when doing LIM most likely. Wonder if you tap on them it will make the car idle worse/better. How old are the plugs/wires?

Cannot say for sure how old the plugs and wires are, i have had the car about a year. I did check them and they seem alright.

did you test the coils with your VOM yet? If so, do they match? (this is important)

I pulled the plugs off each coil pack one by one are seem to be firing alright, one was a little wonky so i swapped it and and didnt help. Do not have anything to fully test coils.

ajgee2011 wrote:

I pulled the plugs off each coil pack one by one are seem to be firing alright, one was a little wonky so i swapped it and and didnt help. Do not have anything to fully test coils.

To test the coils, just pull them one by one (car off of course) and measure:

1. resistance across primary
   
   
2. resistance across secondary
   
   
3. if there is any conductivity between primary and secondary
   

That fully tests the coils.  Any conductivity from primary to secondary and you have a bum coil.  Any coil that is far off in values from the others is a problem too; more on that below.  

Here's your headache: (parts of the following are from http://www.underhoodservice.com/servicing-gm-s-3800-v6-engines/2/)

On this engine, as you know/can see by how it's set up, each coil fires two cylinders at a time; on each firing, one spark plug fires with normal polarity while its companion plug fires with reverse polarity. (by the way this is one of the reasons for all the other electrical fun we have with these cars -- they have what some call a "floating ground.") Because the ignition coil requires approximately 30% more voltage to fire a spark plug with reverse polarity, the ignition coil requires more saturation time (longer dwell) and a higher primary current. This allows the coils to produce up to 40Kv if needed.  AFAIK it's one of the highest energy ignition systems out there *in stock trim* on the SC engine.

The headaches:  the coils for the NA and SC engines are physically interchangeable but electrically different.  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. The SC (supercharged) coils have lower primaries, and higher secondaries, if I remember right, given those ranges.  Point is, if you measure the coils and the values do not match *coil to coil,* that mismatch (plus marginal wires in most cases) will lead to misfiring.  What happens is for one reason or another people get the wrong coils on.  Typically this is when someone with the SC engine gets a coil from a parts store and ends up with a NA coil.  They are sold as interchangeable but that's just wrong -- they will work but they won't work well and fail fast leading to other problems.   Also, because the energy is so high in the first place, worn wires can cause all kinds of problems. More on that later.  Finally, the coils run hot.  If you don't have enough non-conductive tune up grease on the ignition coil ground plate, then the ignition coils will overheat (which maybe might be why your car runs poopy when warm).

If your coils don't match, go to a junkyard and find another car with the 3800 engine same as yours (NA or SC) and buy the coil set.   Measure those with a meter - either at the yard before you buy or at home.  Use the three that match up primary-to-primary and secondary to secondary best, provided they don't leak from primary to secondary. As for wires, you might need to get a set of Delco factory wires.  The energy from this system is really high and it pops or fries  lesser wires quickly over time. The Delco wires don't cost that much even at a GM dealer... but you might try a Delco parts dealer in your town or one of the online merchants via eBay or Amazon.

Finally you need to recheck the wires going into the ignition control module (the coil pack base).  There was a problem with those wires work hardening and breaking inside the insulation, on some of the mid-90s cars.  You will have to check them carefully. Very carefully.

Let us know what you find, we'll continue from there.

Albertj

So i decided to take my care into a different shop. Things were just going a little beyond my knowledge. After 3 days they got back to me and said for starters the intake gasket I just had replaced was leaking along with the thermostat housing. They also said they cannot pin point the exact reason the car is stalling/misfiring yet, but are pretty sure it is an electrical issue, which i was komd of figuring. So hopefully will hear back soon.

I am a body, and stereo guy, I know a good bit about engine work but this was going beyond what I know.

ajgee2011 wrote:

So i decided to take my care into a different shop. Things were just going a little beyond my knowledge. After 3 days they got back to me and said for starters the intake gasket I just had replaced was leaking along with the thermostat housing. They also said they cannot pin point the exact reason the car is stalling/misfiring yet, but are pretty sure it is an electrical issue, which i was komd of figuring. So hopefully will hear back soon.

you could share these posts with the shop....

Will do, will let you know what i find out.

So shop has had my car now sine making this post. They say they hhave tried everything, most recent thing is that they tried 2 different new ECU/PCMs and neither of these have fixed the issue, i have kind of ran out of ideas on this.

ajgee2011 wrote:

So shop has had my car now sine making this post. They say they hhave tried everything, most recent thing is that they tried 2 different new ECU/PCMs and neither of these have fixed the issue, i have kind of ran out of ideas on this.

Hmmm... often with this sort of problem the fix is simple but not obvious. Trying to think of have I seen anything like this before?

This kind of stalling problem can be seen with a dirty IAC circuit - was the throttle body pulled/replaced without thoroughly cleaning it up and replacing or at least resetting the IAC? ?

ajgee2011 wrote:

Hello everyone,
So i have a 95 Riv with a series 1 supercharged. I had it in the shop about 6 months ago to have supercharger rebuilt and the harmonic balancer replaced. After that visit car ran great until a couple months later. Then i would start the car up fine maybe sometimes having a rough idle, but ran fine. After driving for 15 minutes the car would begin to misfire, it would do it until I would pull over and shut the car off. Then I would turn the car back on and it would run fine for the next 15 minutes. I took the car in the shop and they said it was the lower intake gasket or plenum gasket. I got that fixed and the problem was gone. Now a couple months later again the problem came all back again with it misfiring or stalling after about 15 minutes of driving.

Like i said the car sometimes also starts pretty rough and not  idling correctly, and sometimes it will even turn on the check egine light but it goes right off after a restart.

Any help would be appreciated because I am starting to grow sceptical of the shop I am taking it to.

I am still thinking about this. .

I am starting to wonder if you have a failing crank sensor. When they are going bad you can start the car but when they get a little warm they quit. Can't really diagnose because when it fails it does not set a code. You can test them if you pull them, you have to pull the harmonic balancer to pull it though. I think you can also use a Tech I to see if it has quit sending signal during the crank sequence.

My 98, when the first crank sensor failed, come to think of it, it acted just like this. I went around the barn with the service manager at my local dealer about it and finally told them to replace it Customer Request. And that fixed the issue. When the second failed it just died would not start period. That was when I (and dealer)
found out you just don't put in a cheapie crank sensor.


You don't just replace them nilly willy BUT if you have driven more than 2 years / 50K miles since it was last replaced, then it's a good bet for replacement. BE SURE TO USE A GOOD ONE A delco or delphi, not a standard T-series or whatever.

The shop you are taking it to, needs perhaps to see if they are getting a signal from the crank sensor during the startup sequence, and when it stalls warm check again. Also the wiring to the crank sensor could have become bad, it gets hot and oily down there.

Albertj

I did recently have the harmonic balancer replaced, and all of this started happening a couple months after that. I also noticed something today, not sure if it is related but when i really get on the gas in 1st or 2nd gear sometimes i hear a loudish rattle coming from the engine. And this is my second Riv that i own i have a 98 supercharged and a 95 supercharged, the 98 has 295,xxx miles on it and the 95 has 150,xxx on it. But i notice a big power difference between the 2 with the 98 having more power and better response than the 95 that is curretly have the issues.

And the car is not completly shutting off it is just misfiring after warming up and sometimes it can be random doing it some days and not others, and it only seems to do it driving on the highway.

Damn.....

ajgee2011 wrote:

And the car is not completly shutting off it is just misfiring after warming up and sometimes it can be random doing it some days and not others, and it only seems to do it driving on the highway.

Then your check engine/service engine soon light is "on" right?

You/your mechanic will need an appropriate scan tool (not just code reader) to catch this gremlin, and/or maybe an oscilloscope. IIRC the 95 is OBD1 via an OBD2 port. Maybe an Innova 3120? not sure. A GM Tech I Definitely.

I did a quick web search and found causes could include coils (look out for lower output when warm), injectors (something partly clogging one or more), the fuel pressure regulator (leaky but not failed), spark plug wires (conductors and insulators have issues after a long time in service). There is a lot of other info on this site about all of the above.

Thanks for the clarification, FWIW misfiring under load I'd check those coils and wires if you have not already in tracking down this particular issue.

So update on how things are going, after the shop had the car for 2 months theu ended up replacing all plugs, wires, and coils. And they also replaced the camshaft position sensor. After getting the car back it drove great for a couple weeks, then something new came along. The car started shifting wierd. Shift fine into 1st and 2nd, but the when it shifts into 3rd then seems to pause for a second then shift again all while the rpms drop from around 2500 to 1500, when it does the pause you can really feel it shift. It also completely died pn my while day while i was driving about 50 or 55. I pulled over and tried to restart it, and it would start. Ilet it sit for about a minute and tried again and it fired up and drove great. That only happened once and after its been fine for the past 3 days, besides still shifting wierd. And one last issue is that sometimes when i start the car it seems to start a little rough amd the check engine light comes on, i shut it off and start it back up and seems to start a little smoother with no check engine light, this is a daily occurance with thale starting issue.