I have a 1995 6M Z28 with around 120k miles on it. I was having some problems with cold starts in humid/wet weather, misfires, and finally it would, albeit very rarely, stall out on me during idle so I decided to replace the coil. I did that last week and overall driveability has improved.

The cold start issue has not resurfaced yet (although it's been pretty dry lately) and the misfires appear to be gone... unfortunately on the way home today it stalled out when I was sitting at a stop light. When I tried to restart it cranked but didn't sound or feel at all like there was combustion going on. After sitting there for a few minutes it finally restarted. It started dying on me again at the next stop light. When I tried to add a little gas it stalled out completely. Again I was able to restart it after waiting around 60 seconds. When I finally pulled into a parking lot I let it idle which it did fine for a while and then it started to drop down to around 500 RPM and then jump back up to 900... it did that a few times and eventually it stalled out.

It runs fine during driving.. the only time it stalls out is when it's idling.

Any suggestions? I replaced the opti, wires, and plugs around the 80k mark and the fuel pump early this year (110k mark). I'm thinking the Ignition Control Module but not sure how to isolate it as the source of the problem. I have an OBDI PCM with an OBDII connector so Autozone won't read the codes for me (if there are any).

-Wayno-san

 

Sounds to me like your injectors need professionally cleaned. At idle, the PW is reduced and it may be a partial blockage does not allow enough fuel. Once it's running under load, it may be getting just enough fuel to run. If you could scan the O2 and fuel trims, you maybe able to confirm such an issue. Easiest way to clean them is on the rails with a product like 3M has.

 

Speedygonzales,
Thank you again for the quick reply. I replaced the fuel filter a number of times (3 I think) during the car's life, the last of which was when I replaced the fuel pump earlier this year (which you helped me with-again, thanks).

I was thinking about your diagnosis and I'm wondering... if this is dirty fuel injectors wouldn't the problem occur frequently and also cause a rough idle most of the time? From what I recall of the stalling it's only happened maybe 3 times (not including the instances yesterday) and everytime it was when the engine was already warm. Otherwise it idles just fine.

What is the acronym PW stand for? (?Pulse-width?)
When you say professionally cleaned does that mean I cannot do it?
Do you recommend a dealer perform this procedure or will a typical automotive service center be able to handle it?

Thanks again,
Wayno

 

Yes PW is pulse width.

Remember that while the engine is cold, that is in open loop, the PCM enriches the fuel mixture. Possibly overcoming a minor blockage. Once it cuts the fuel back, it may be running too lean. Not a good thing. The plugs will tell the story of a lean or rich engine.

You can do the cleaning yourself but it is expensive for the equipment. You need a hose assembly that connects to the fuel rails. A refill can is attached to the hose and the fuel pump is disabled as well as the regulator. The engine is started and allowed to run on the can of cleaner only until the engine stalls out. The cleaning is then finished. I just looked at 3M's website and found basically what I have. http://solutions.3m.com/wps/portal/3...glQF2T43N7Q7bl
That system uses this.
http://solutions.3m.com/wps/portal/3...beGSJX1THS8Hgl
But those kits are over 300. Mine at the time was around 100 because it does not use a regulator.

The corner garage may or may not have a kit to connect a cleaner to the fuel rail and have the engine run off only the cleaner. Most just hang a cleaner over the engine and allow it drip into the intake. Which obviously does nothing for the fuel system. Cleans the intake and valves which is ok but not your problem.

The other solution is to remove the injectors and have them cleaned. You could also raise the fuel rails and have someone crank over the engine to see what the spray pattern looks like on all 8 compared to one another. Just my .02

 

speedygonzales,
Thanks for the info... I haven't had the engine stall out yet since the instances on 10/14. I'm running a bottle of the Techtron fuel system cleaner in the gas tank per the recommendation of a friend. Maybe I got some bad gasoline somewhere?

I like your last suggestion or raising the fuel rail... will look through the manual to see how difficult this is going to be.

I the meantime I REALLY REALLY need to get some new tires and a battery for the car before winter sets in. Tires are well past the wear indicators and the battery, even though it's an Optima, is over-due for replacement. Amazingly it has lasted around 7 years so I feel I got my money's worth.

Will update once I make some progress.

Peace,
Wayno-san

 

120k miles?! Stalling at idle could be caused by a gunked up throttle body. Get some TB spray and clean the IAC, the butterfly plate and passages.

 

Could be your EGR valve sticking open.

 

I'm waiting on a buddy to get a code scanner for me. Want to check if the O2 sensors are working properly. Not sure if OBDI sets the service light for these if they're have issues.

I checked the TB and it does have some gunk on it but appears to be closing completely. I assume I can spray some carb cleaner in there while the engine is running or is that a bad idea? (to clean it)

Does the EGR have a feedback signal that I can check with the scan tool?

 

Not on an LT1. You can manually manipulate the valve diaphragm to see how it is acting. There is some EGR info on my Tech Page.

 

After taking a service hiatus for the winter I need to get back and fix my Camaro. During winter I ended up getting 4 new Falken's and I'm pretty happy with them. Winter traction is adequate and they grip well in the rain and dry.

During winter the car ran OK and didn't stall out on me at all (like in the fall). I still had to crank it excessively after it sitting overnight if the conditions were humid but it always started quickly the rest of the day. The three issues I had this winter were 1) someone ran into it and cracked the driver's side panel, 2) front passenger side shock blew out (Monroe sensa-track (second time)) and 3) the coolant hose coming back from the heating core sprung a pin-hole leak. Luckily I was not far from home and was able to drive it back with cooling breaks/adding water. Not surprising I guess for it being a 14 year-old-car. I should probably replace all the hoses once the weather gets nice.

Unfortunately this past Friday the car started to misfire and stall out again. I also haven't been able to restart it because it's been raining and humid. Since the start issue happens only when it's humid/raining I'm assuming this either has to be the opti or the plug wires? Typically it will start after a few long cranking events but it was REALLY wet this weekend.

I'm going to pick up one of those HEI test plugs after work today to test for spark. I'm assuming that if I want to check for corona/shorts I'd probably need to get the car up on ramps and look from underneath? I last had the spark plugs/wires replaced by the dealer in 2003/72k miles for the labor cost of $350 with MSD 8.5mm "Superconductor" wires and some Platinum Bosch plugs (paid for separately). Should I try to test the wires or am I better off just plopping down another $100 for a new set? Plugs look like a PITA so I'm contemplating having the dealer do it again if they'll do it for a similar fee.

Comments/Suggestions?
-Wayno-san

 

Spoke with a buddy of mine today who has an LT1 Firebird of the same year and he stated that he too has a lot of difficulty starting his car when it's humid or raining. He's never fixed the issue and instead just parks the car in the garage (apparently this allows him to work around the problem). Unfortunatelyh I do not have this option. Anyone else have this problem and, if so, how did you fix it?

Thanks,
Wayno-san

 

As I mentioned above, with 120k miles on the clock your throttle body will have a significant amount of gunk in it. This will affect the idle quality and may contribute to stalling. While I am not sure it is the cause of your problem, it would still be advised to clean it carefully and rule that out.

I would suggest that you remove it and partially disassemble it and clean it. Just spraying carb cleaning in a few passages doesn't alway get it clean. I was amazed at the amont of gunk mine collected at less than half the mileage of yours.

 

Don, thanks for the info... there's a procedure for using "Seafoam" to clean the engine on the MI F-Body website:

http://www.mifbody.com/vbulletin/tut...=view&tutid=11

Would you guys recommend doing this? I've never flooded an engine with stuff like this and I'm not convinced that it's safe/good for it.

Good news! I was able to borrow a Tech 2 to use to diagnose the problem(s). I only have this thing for a day, two at the most, so I need to make sure I have a plan. Aside from pulling DTCs, do you have any recommendations on which PIDs I should check and what reasonable ranges should be? I was thinking I could take a look if the O2 sensors are working as they can make the engine run rich, and I've been getting ~15MPG ave. I can probably check injector signals (I hope)... not sure about OBDI though so I do not know what is / is not going to be available.

Thanks again for all the help!

 

Guys,
I played around with the Tech 2 last night and unfortunately was not able to find anything right off the bat that is the source of the issues. No PT DTC aside for the skip-shift feature, which I have disabled. I did find history (but not current) Chassis DTCs which probably explain why the ABS works so crappy. They were:

C1263 – RF ABS Motor Circuit Shorted to Voltage
C1287 – Red Brake Warning Lamp Circuit Open (is this the IP lamp? If so, it appears to be working fine)
C1357 – Left TCS Motor Circuit Shorted to Ground

I’ll deal with these later.

I jotted down what was going on from about 8 to 16 minutes of idling and this is what the Tech 2 showed:

Idle: 800RPM
ECT: 156F (ended up 204F after 16 minutes)
IAT: 62F
MAP: 32kPa
BARO: 101kPa
BARO: 4.90V
TP: 0.60V
TP: 0%
Left HO2S Bank 1: Varied wildly between 30-800mV (This means it’s working properly correct?)
Right HO2S Bank 1: Varied wildly between 30-800mV
Loop: Closed
Short Term FT Bank1: 123 counts
Long Term FT Bank1: 120 counts
Short Term FT Bank2: 125 counts
Long Term FT Bank2: 120 counts
Fuel Trim Cell: 16
Fuel Trim Enable: Yes
Spark Advance: 20degrees
MAF Sensor: ~8g/s
Knock Retard: 0degrees
KS Activity: 13 counts
Knock Sensor: OK
Low Res Signal: ~18ms
High Res Signal: Yes
Injector PWM Bank 1: 2.8ms
Injector PWM Bank 2: 2.8ms
IAC Position: 42 counts
Learned IAC: 35 counts
EGR Duty Cycle: 0%
AIR control: OFF
System volt: 13.3V
EVAP Canister Purge: 0%
Injector Fault: No
Fan Ctrl PCM A10 (if equipped): OFF (What is this?)
Fan Control PCM A11: OFF

I also observed the following:
• When I command the Evap Purge Solenoid ON both oxygen sensors go to ~20mV so it looks like they are fine.
• When I command Open Loop Status it turns off fuel trim.
• When I disable an injector (any injector), the Low Res signal goes from ~16.5 to 17.5ms.
• I never see the EGR open when driving, but I can hear a little “click” sound underhood when I command it open

Of course it started and ran fine all the time I had the scan tool attached… will drive it around and hopefully it will start stalling out so I can capture the data. Not sure if I’ll be able to get the data off of the tool though….

Peace!

 

Yesterday after about 35 miles of driving on the highway I stopped at a fast food joint. After grabbing a bite to eat I started the car and began to pull of the lot. It started stumbling and stalled out on me. I had the Tech 2 connected at the time and recorded the event until stall. Unfortunately I do not know how to download the data onto a PC, or even if it's possible. I have to return the thing tomorrow so hopefully my buddy will be able to pull the data off of it. In summary, the engine stumbled around a lot at low RPMs and eventually went into Open Loop mode and both O2 sensors dropped to <10mV. Ran like that for a while until eventually it died. The only thing of note that I can tell from looking at the data is that "Injector PWM Bank 1" was on longer the majority of the time when it was stumbling... usually by 2ms or so.

I checked for DTCs afterward and saw 0044, "Bank 1 O2 Lean Exhaust Indicated". The O2 sensors appear fine as they passed the O2 test which I ran later that day after the car acted normally again.

Unfortunately when I rolled into my work parking lot this morning I noticed a lot of smoke coming out of the tailpipe. This does not look good. I made a little video clip with my phone. White smoke means coolant right?

http://www.youtube.com/watch?v=usjv9_Dnepw

Is it safe, albeit not socially responsible, to drive it like this?

Thanks again for the help! Not sure if I should continue trying to fix (and put money into) it or hope that that clunker bill gets passed and get a new car.... :/