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FIXITMAN
FIXITMAN, Mater Technician
Category: Pontiac
Satisfied Customers: 17406
Experience:  ASE MASTER CERTIFIED, AA DEGREE AUTO/DIESEL TECH
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I would like to continue the conversation on my 1998 Grand

Customer Question

I would like to continue the conversation on my 1998 Grand Prix GTP. When I follow this link: http://mail.justanswer.com:80/track?mailingid=AnsNotEToC&messageid=325&databaseid=0&type=click&serial=635672581391289343&emailid=*****@******.***&userid=86361370&extra=&&&3&&&http://www.justanswer.com/pontiac/9381m-pontiac-grand-prix-1998-pontiac-grand-prix.html?L=T&jats=793624D520F149E8BD26496F3C09FA6C&utm_source=sys&utm_medium=email&utm_content=expert_im&utm_campaign=ir_ppq_a&r=ems%7C2015-05-15%7C325%7Cln=expert_im
I don't get a reply button. I still have the issue, (P300 on WOT), and have tried a few of your suggestions
Submitted: 2 years ago.
Category: Pontiac
Expert:  FIXITMAN replied 2 years ago.
Would you like to continue here or at the previous post?
Customer: replied 2 years ago.
I'd like to follow up on the previous post, but there is no "send" or "reply" button. If you can get the prior one turned on, that would be cool.Here's the current status:
I ordered and installed a new ignition control module. This had no effect, still get the P300 with a noticeable miss above about 3500 at wide open throttle.Next step, I started looking for a failed intake system gasket, as the problem only occurs when under boost and load. I disassembled the supercharger from the intake manifold, and that gasket was ok. But the gasket between the throttle body and the supercharger inlet looked like it had failed around the coolant passage. Coolant is routed up through the s/c body and around the EGR inlet and into the back of the throttle body - it looked like it could have been pulling coolant into the intake charge from this location. I replaced both the s/c -> plenum and s/c to throttle body gaskets, and tried again. The first hard pull at WOT didn't throw any code, and there as a slight miss at about 3800. I then tried a second and third pull, and these set the P300 code again, with a noticeable intermittent miss above 3500. In the past, any WOT pull going past 3500 would cause the P300 to set - this time it didn't set on the first pull.So now I'm wondering if the HO2S has been contaminated by coolant in the exhaust? What is the best way to test the O2 Sensor? There are no other codes, just P300.Of course, any other suggestions are welcome. I can get & post the freeze frame data if that would help.Thanks;Glenn
Expert:  FIXITMAN replied 2 years ago.
Thanks Glenn. If you can post the freeze frame data that would be great and may help us find the issue.
Customer: replied 2 years ago.
Ok, here's the FF data:
P0300 is the DTC that caused this Freeze Frame Data to be Stored
Random/Multiple Cylinder Misfire Detected
Fuel System 1 Status Open Loop Control - Warmup
Calculated Load 60.4 %
Coolant Temperature 87 °C 188.6 °F
Short Term Fuel Trim Bank 1 0.78 % Lean (-)
Long Term Fuel Trim Bank 1 13.28 % Lean (-)
Manifold Absolute Pressure 142 kPaA 20.6 PsiA
Engine Speed 3615 Rpm
Vehicle Speed 92 Kmh 57 Mph
Mass Air Flow 157.45 g/s 20.8 lb/min
Absolute Throttle Position 99.6 %Could it be that the ECU needs time to reset the fuel trim after the coolant is no longer getting into the intake?Thanks;Glenn
Expert:  FIXITMAN replied 2 years ago.
From the readings it seams like the fu trim is low. This does have a new fuel pump on it, right/
Customer: replied 2 years ago.
The fuel pump was replaced 22 months ago (9/2013). I have done the Fuel System Pressure test for VIN 1 as shown in the FSM. It calls for 48-55psi static with ignition on but not started (after pump shutoff). I get a consistent 48psi. The idle pressure should be no more than 3-10 psi less - I get 48psi again (drop of 0), Applying 12-14 inches of vacuum to the fuel pressure regulator should have a drop of 3-10 psi - I get a drop of 6 psi. These all look within spec (albeit on the low side for static pressure). These tests were all done before I replaced the fuel filter. The fuel filter was replaced (part of the diagnosis for this issue), the fuel injectors were replaced in January of 2010, and had an ultrasonic cleaning and flow verification as part of this diagnosis. I can't see my fuel pressure gauge during the road test (where the misfire occurs) without removing the hood (which I can do if that makes sense). I have seen some chatter on the internet about the fuel pump resistor - is that a possible cause?Wouldn't the fuel trim being on the lean side indicate that the O2 sensor is seeing a richer than desired condition, and the ECU is commanding it lean to compensate?Thanks;Glenn
Expert:  FIXITMAN replied 2 years ago.
I would typically use a longer hose and tape the gauge to the windshield and watch the pressure during the issue. As for the resistor that is definitely a high possibility. Typically they fail completely and the car will not start at all, but if it has internal resistance then it will stop building good pressure at certain times. It is located inside of the passenger wheel well.
Customer: replied 2 years ago.
Ok, sorry about the long delay. I extended my fuel pressure gauge, and the pressure is no lower than 42psi during cruise, and increases under WOT acceleration to about 58psi, and stays there rock solid, even when the SES light starts flashing. So it's not insufficient fuel pressure, or likely flow either.Could the O2 sensor have been ruined by the coolant in the mixture, and is now reading incorrectly? The misfire is much less severe now - it's more like a decrease in power from what you would expect, and doesn't necessarily set the P300 on every WOT throttle run. Usually the first one after warmup to 180degrees doesn't set the code, but the second and subsequent ones do...usually.
Expert:  FIXITMAN replied 2 years ago.
The O2 sensors could have definitely been damaged from the coolant. It could have also damaged the converter.
Customer: replied 2 years ago.
Ok, I'm still in there swinging on this one - I've replaced the front O2 sensor, and the EGR tube that goes from the EGR valve to the intake manifold - it had a hairline split in the crimp where the clamp pressed it against the intake. Still no change, although all the things I've done together have improved how the car runs - Now it takes longer at WOT to throw the P300 code, usually it won't set the code on the first WOT run (up to about 75), but will eventually on the second and subsequent ones, although it isn't nearly as soon as it used to be. I can still notice when the car starts to mis-fire, the acceleration rate falls off a bit, but it still pulls.Any more ideas on what to check to isolate the issue?
Expert:  FIXITMAN replied 2 years ago.
What is the ignition timing reading on the scan tool when the 300 code comes up?
Customer: replied 2 years ago.
Sorry it took so long, but I have some data. I've tried to attach a spreadsheet with a couple of charts - the most interesting one is the one labeled "One run".I did two acceleration runs, and both of them triggered the P0300 code. Basically the spark advance for #1 stays at about 12-15 degrees, and doesn't change much when the P0300 code triggers. You can see that the acceleration in first gear isn't as steady as you would expect, then after the 1-2 upshift, the acceleration rate gets more variable, and the P0300 code triggers. The spark advance is at about 13 degrees when it triggers. There is no significant change to the timing when the code triggers.It won't let me attach the file - Do you need to do something to allow that?
Expert:  FIXITMAN replied 2 years ago.
Have you taken your fuel trim readings?
Customer: replied 2 years ago.
Ok, I was able to attach the file - let me know if you can't read it, or if you have questions.
Expert:  FIXITMAN replied 2 years ago.
Any fuel trim readings?
Customer: replied 2 years ago.
Here's the Freeze Frame data for one of the P0300 triggers:
EasyObdII - Freeze Frame Data Report for 327BGN at 23:33
P0300 is the DTC that caused this Freeze Frame Data to be Stored
Random/Multiple Cylinder Misfire Detected
Fuel System 1 Status Open Loop Control - Warmup
Calculated Load 60.4 %
Coolant Temperature 87 °C 188.6 °F
Short Term Fuel Trim Bank 1 0.78 % Lean (-)
Long Term Fuel Trim Bank 1 13.28 % Lean (-)
Manifold Absolute Pressure 142 kPaA 20.6 PsiA
Engine Speed 3615 Rpm
Vehicle Speed 92 Kmh 57 Mph
Mass Air Flow 157.45 g/s 20.8 lb/min
Absolute Throttle Position 99.6 %
Customer: replied 2 years ago.
I didn't log the fuel trim while logging the spark advance
Expert:  FIXITMAN replied 2 years ago.
It looks like you have a lean condition going on. Can you install your fuel pressure gauge and attach it to the windshield and see what it reads while driving?
Customer: replied 2 years ago.
I did that, it was rock solid at about 58psi during the WOT run, even when the engine was mis-firing and setting p0300
Expert:  FIXITMAN replied 2 years ago.
When you pulled the super charger did you also pull the lower intake manifold?
Customer: replied 2 years ago.
Not the last time. I had the lower intake repaired (it was leaking coolant) about 18 months ago, and it was off then of course.
Bad fuel injectors? (had them ultrasonically cleaned and the flow tested ok)
Intermittent open in the injector wiring?
ECU outputs that won't drive the injectors?
Expert:  FIXITMAN replied 2 years ago.
I do not think it is the injectors. I think you either have an issue with the lower intake, or you have an O2 sensor issue. I have also seen a failing converter cause this in some cases.
Customer: replied 2 years ago.
I recently (within the last month) replaced the front O2 sensor. The rear one is 2-3 years old. I have the original converter on the car, but I have a new one I could reinstall (I didn't want to ruin the new one with the misfire condition). Are you thinking a leaking lower intake gasket?
Customer: replied 2 years ago.
What should I look for if I pull the lower intake?
Expert:  FIXITMAN replied 2 years ago.
Yes, I am thinking that there is air getting by the intake.
Customer: replied 2 years ago.
Air going past the MAF, but not getting to the cylinders (leaking out of the intake)? Wouldn't that make the mixture rich, as more air is going past the MAF than is getting into the cylinders?
Expert:  FIXITMAN replied 2 years ago.
Actually the intake leak allows the cylinders to draw in more air than what the MAF tells the computer so it would show a lean condition.
Customer: replied 2 years ago.
With a supercharged engine? At WOT, the pressure in the intake is 4-7 PSI greater than the external air pressure (per my boost gauge), so if there's a leak, then the air in the intake should flow out of the intake to outside, rather than in from the outside.
Expert:  FIXITMAN replied 2 years ago.
It comes back into to the intake system as it will build internal crankcase pressure.
Customer: replied 2 years ago.
I was finally able to get my OBD scanner to cooperate, and give me readings for short and long term fuel trim and both O2 sensors during a acceleration run. I've attached the same spreadsheet as before, with new tabs OneRun20150907, TwoRuns20150907and EasyLogger9715103303. The interesting one is the graph of one run - it shows O2 sensor 1 (ahead of the cat, I believe) with a constant rich condition (0.9+ volts) throughout the acceleration run. It looks like my scanner only reports zero or positive values for PIDs, as the STFT went to zero almost as soon as the run started (I would expect it to be some negative percentage, trying to lean out the mixture). What looks odd to me is the behavior of O2 sensor 2 - Should it go all the way to zero? And how can there be MORE oxygen after the catalytic converter than there was before it? If O2#1 is correct, then I'd think there's a good argument for a leak in the intake tract. Ideas?
Expert:  FIXITMAN replied 2 years ago.
Thanks for getting back with me. It should go rich during acceleration but it should level off and drop down closer to 0 when cruising. The rear reading is fine and should be more stable as it appears to be. What did bank 2 sensor read?
Customer: replied 2 years ago.
There are no bank 2 sensors - it only has 2 oxygen sensors, one in front of the cat, and one behind.
Expert:  FIXITMAN replied 2 years ago.
I did not see a spread sheet. Can you try attaching it again?