Cold Problems with My Grand Prix

When cooler weather arrived I began having problems with my '98 Grand Prix GT (with a cold air induction system, cat-back custom exhaust, and performance PCM). When I first start it, it runs rough (missing, shaking, idling erratically). Once it warms up, it's just fine. I've had it to the dealer and they can't figure it out. The engine has been tested for gasket and vaccum leaks - everything checks out fine. I've replaced a couple of sensors (the air idler control and the air intake temp). I relocated this latter sensor closer to the source of the air, as suggested by a website and this has made no difference. I've listened to my fuel injectors and each one is clicking. I replaced my fuel filter and can hear the fuel system pressurizing when I turn on the ignition. Autozone tested my throttle position sensor as well as my coils and they tested out fine. The car had a complete tune up about 4 months ago (new plugs, wires, pvc valve). I'm baffled and frustrated. I've now spent over $240 on this problem and it still exists. One tech suggested that I move to a warmer climate...not a bad idea, just not practical. I'm hoping somebody has had a similar problem and can provide a solution.

You didn't say whether or not you have any check engine light or stored codes, or if you tested what your fuel pressure reading is at the rail. It's possible to get a bad new plug or wire (what brand did you install?) and did you get the MAP sensor seated when you changed the PCV?

I do have a check engine light - a generic misfired code on all cylinders, according to the dealer. I have not tested the fuel pressure at the rail. The MAP sensor is properly seated. Another person suggested that I replace my plug wires, even though they're relatively new, because sometimes they may have a fracture due to bending or manufacturing flaw - I installed 7mm Autolite wires from Autozone, AC Delco factory replacement plugs. Many thanks!

If you have access to an old timing light, you can use it to test spark on each cylinder. Hook the inductive pick-up on each wire and fire the timing light to a dark area under the hood. Any that don't have a constant flash are where your problem lies. If all the plugs are firing steady, then I would say you may have an injector problem.

If you did not have this problem before putting in the Autolite plug wires then you might consider switching back to the OEM AC Delco Packard 7mm plug wires. The AC Delcos have the best conductivity and least amount of resistance.

On a P0300 misfire code the most likely possibilities are poor engine vacuum, ignition, air intake or fuel (injectors).

Since you have a CAI installed, try cleaning the throttle body especially the place where the IAC mounts. Also clean the throttle body screen and the Mass Airflow (MAF) sensor. Until the engine warms up fully the PCM operates in the open loop mode and depends on the signal it receives from the MAF sensor.







http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

After $218 later (crankshaft relearn procedure, short and long term fuel trim % test, fuel pressure and volume test, cylinder balance test, ignition leak test, spark shut down test, injector specs test and an injector pulse trace - and all this was after the dealer charged me $135 for a diagnosis that was unsuccessful) my repair shop says i have three injectors failing and a weak downstream O2 sensor. The shop recommends replacing the injectors with performance injectors b/c I have a PCM from Digital Horsepower, which the shop claims may cause a high failure rate in stock injectors. (Is this true?) So I now plan on replacing my injectors and at $80 a pop for Autozone's OEM replacements, I'd just assume buy performance injectors. But I am not sure which way to go. The stock ones allow 22 psi - should I stick to this or get some with more or less pressure? I don't plan on doing anything with the stock fuel press. regulator. The shop said my fuel pressure tested at 54 psi - I don't recall what the number was for the volume but the shop indicated it's a healthy one. I'm still leaning toward new wires and possibly coils but I admit I don't understand all the numbers assocaited with the product descriptions. Any advice on the injectors would be great, as would any additional advice on the ignition upgrades. Just to recap, I have a '98 GP GT with a Thrasher CAI, a DH PCM and a Flowmaster cat-back exhaust. My car has 73K miles on it. Thanks guys!

If you did not have this problem before putting in the Autolite plug wires then you might consider switching back to the OEM AC Delco Packard 7mm plug wires. The AC Delcos have the best conductivity and least amount of resistance.

On a P0300 misfire code the most likely possibilities are poor engine vacuum, ignition, air intake or fuel (injectors).

Since you have a CAI installed, try cleaning the throttle body especially the place where the IAC mounts. Also clean the throttle body screen and the Mass Airflow (MAF) sensor. Until the engine warms up fully the PCM operates in the open loop mode and depends on the signal it receives from the MAF sensor.







http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

After $218 later (crankshaft relearn procedure, short and long term fuel trim % test, fuel pressure and volume test, cylinder balance test, ignition leak test, spark shut down test, injector specs test and an injector pulse trace - and all this was after the dealer charged me $135 for a diagnosis that was unsuccessful) my repair shop says i have three injectors failing and a weak downstream O2 sensor. The shop recommends replacing the injectors with performance injectors b/c I have a PCM from Digital Horsepower, which the shop claims may cause a high failure rate in stock injectors. (Is this true?) So I now plan on replacing my injectors and at $80 a pop for Autozone's OEM replacements, I'd just assume buy performance injectors. But I am not sure which way to go. The stock ones allow 22 psi - should I stick to this or get some with more or less pressure? I don't plan on doing anything with the stock fuel press. regulator. The shop said my fuel pressure tested at 54 psi - I don't recall what the number was for the volume but the shop indicated it's a healthy one. I'm still leaning toward new wires and possibly coils but I admit I don't understand all the numbers assocaited with the product descriptions. Any advice on the injectors would be great, as would any additional advice on the ignition upgrades. Just to recap, I have a '98 GP GT with a Thrasher CAI, a DH PCM and a Flowmaster cat-back exhaust. My car has 73K miles on it. Thanks guys!

Are these injectors good replacements for my situation?

http://zzperformance.com/products1.php?id=297

After $218 later (crankshaft relearn procedure, short and long term fuel trim % test, fuel pressure and volume test, cylinder balance test, ignition leak test, spark shut down test, injector specs test and an injector pulse trace - and all this was after the dealer charged me $135 for a diagnosis that was unsuccessful) my repair shop says i have three injectors failing and a weak downstream O2 sensor. The shop recommends replacing the injectors with performance injectors b/c I have a PCM from Digital Horsepower, which the shop claims may cause a high failure rate in stock injectors. (Is this true?) So I now plan on replacing my injectors and at $80 a pop for Autozone's OEM replacements, I'd just assume buy performance injectors. But I am not sure which way to go. The stock ones allow 22 psi - should I stick to this or get some with more or less pressure? I don't plan on doing anything with the stock fuel press. regulator. The shop said my fuel pressure tested at 54 psi - I don't recall what the number was for the volume but the shop indicated it's a healthy one. I'm still leaning toward new wires and possibly coils but I admit I don't understand all the numbers assocaited with the product descriptions. Any advice on the injectors would be great, as would any additional advice on the ignition upgrades. Just to recap, I have a '98 GP GT with a Thrasher CAI, a DH PCM and a Flowmaster cat-back exhaust. My car has 73K miles on it. Thanks guys!



If you plan on modding extensively including a hot cam and roller rockers, etc. they are a good choice. Otherwise the stock fuel injectors are fine.

I've never heard of a DHP re-programmed PCM causing injector failure.

The fuel pressure test at 54 psi is good.

Also, how old is your CAT convertor and is it stock or aftermarket?







http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

have you tried cleaning out you injectors-
did this on my civic:
with the motor running, pull a vacuum line that goes to the motor, preferably the one going to the brake booster. car will start to run rough. put the hose in a glass with about 12 ounces of pure injecter cleaner from you local auto parts store. car will chug and die. let sit for 10 mins. reattatch vac. line and restart car. will crank for a while but will eventually start. lots of blue smoke for a while. the benefit of doing this is that the cleaner is not mixed in your gas tank with 15 gals of gas, it is shot straight throught the injecters. buddy of mine wrecked his injecters trying to pull them out and clean em.
hey bnayler- ever heard of this procedure?

have you tried cleaning out you injectors-
did this on my civic:
with the motor running, pull a vacuum line that goes to the motor, preferably the one going to the brake booster. car will start to run rough. put the hose in a glass with about 12 ounces of pure injecter cleaner from you local auto parts store. car will chug and die. let sit for 10 mins. reattatch vac. line and restart car. will crank for a while but will eventually start. lots of blue smoke for a while. the benefit of doing this is that the cleaner is not mixed in your gas tank with 15 gals of gas, it is shot straight throught the injecters. buddy of mine wrecked his injecters trying to pull them out and clean em.
hey bnayler- ever heard of this procedure?

lol. :lol2: No, can't say I have JimmyV. But here's one that I've used and it works plus sounds a little more kosher. Total cost for parts came out to $50 with an Actron Fuel Pressure Tester from Autozone.

Check out this link

http://www.dans-website.com/cleaning_injectors.htm

I agree pulling the injectors is not the way to go unless you've proven they are bad with a Noid light or coil resistance test. According to GM, 6 out of 10 injectors suspected bad are actually just dirty.






http://i5.photobucket.com/albums/y186/lizzywiz/gtp.jpg
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.

Thanks, guys. I replaced all of my injectors on the "front" of the engine and that has fixed my problem. When I removed the old injectors from the intake, I noticed some grit where they should have been sealed. (The intake gasket was replaced in February.) Makes me wonder if my O-ring seals just needed replaced. I put new seals on the old injectors and lubed all 6 of the rings with plug wire grease. I'm a bit stumped, though, because before I replaced them I listened to all of the injectors with a stethoscope and could hear each one clicking and their resistance was fine.