02 Grand Prix SE 3.1

[cool02grandprix]

Ok I will try that,,,,,,What should the fuel pressure be at the rail./.

Brian

[BNaylor]

Originally Posted by cool02grandprix

Ok I will try that,,,,,,What should the fuel pressure be at the rail./.

Brian

Fuel pressure will vary depending on the year of your Grand Prix and engine size. For GPs with the SII 3800 VIN "K" and "1" the target is 48-55 psi at fuel pump prime (ignition to on). Then you will have different readings at idle because vacuum is connected at the fuel pressure regulator (FPR). So you will remove the vaccum line at the FPR and reconnect and then review a total of three readings. Further, this will test the fuel pressure regulator located at the front fuel injector rail (driver's side) in addition to the fuel pump pressure.

The fuel pressure on GM cars with the 3100/3400 60 degree VIN "J" and "E" engine is most likely going to be higher than above. Also, it is a good idea to have a new fuel filter if it has not recently been replaced.

Here is an Actron fuel pressure tester connected to a 3400 VIN "E" and the reading at idle is well over 55 psi.

[bricker82]

I had this exact same problem on my 2000 GP before and the dealer thought it was the cat converter, which was still under GM's 8 yr/80,000 mile warranty on exhaust. So they replaced it, after 3 days of agonizing wait due to them ordering the wrong cat , and I drove it home. And they forgot to put the donut back on...I sounded like a diesel going down the road!

However, I still had the problem. I had also changed the plugs and wires recently. Same code too, come to find out I had 2 bad coils, generating no spark to the cylinders, thus multiple misfires! Replaced them and away I went.

Hope this helps!

[cool02grandprix]

Ok here I go


I went and got a vacuum tester

results
----at idle I had about 14-15 in hg.

----reved to 2000 to 3000 rpm vacuum decreased to 10-13 in hg..

and once idled back to normal around 15 in hg.

and one more thing, with the car starting so good and idling almost perfect, is there any chance of a bad coil pack....the post above this one had the same problem and his was 2 bad coil packs.....

also bricker82 a question for you, How was your start up and idle?


Thanks

Brian

[bricker82]

It was a normal startup and idle after the cat was replaced. Just the same thing when I accelerated, bogged down with minor shaking!

[BNaylor]

Just to be sure what brand spark plugs and ignition wires did you install?

BTW - The vacuum reading at 2000 rpms is abnormal but it is hard to say whether the coils are having the effect on your low engine vacuum problem.

You can check coil primary and secondary resistance with a DMM or use coil tester.

[BNaylor]

I ran this test at 1500 and 2000 rpms respectively so you can run a comparison. Engine vacuum held steady at least 18 in hg and stayed in the green area at both rpm ranges. Your reading is way too low. See below. Idle was 16 in hg.

[cool02grandprix]

ok I went and got a vacuum tester like you have.....

at idle I get 13-14 in hg
rev to 2000 to 3000 and it drops to basically to about 0 (zero) and then at idle back to 13-14 in hg

[BNaylor]

Originally Posted by cool02grandprix

ok I went and got a vacuum tester like you have.....

at idle I get 13-14 in hg
rev to 2000 to 3000 and it drops to basically to about 0 (zero) and then at idle back to 13-14 in hg

Basically we can only give you advice. The decision on what corrective action to take is yours. Based on what I see on the results you have exhaust restriction. Your vacuum readings are definitely abnormal.

Once you have ruled out misfire cause by ignition or a fuel related problem I would seriously consider getting the CAT convertor tested and replaced.

[cool02grandprix]

Just an update on my Grand Prix


Ok I removed my cat, and replaced it.

The engine runs awesome now,,,Has more power now than when I bought the car.

I rechecked my vacuum and it is perfect at idle and 2-3k rev..

My car also runs cooler now, I was having overheating problems before

I just want to say thank you to all the people who helped with the advice, I would have been lost without your help...

I ended up just spending $300 for a new cat and 2 new O2 sensors and put it on myself....

Thanks again......

[clutch492]

Bnaylor is right! I thank him for this post. I have been searching for this same problem on my car.

I saw this post. I checked the vacuum on the engine. It went low as soon as I would touch the gas pedal. I drilled a hole in the exhast pipe on the inlet side of the cat converter and used my bore-scope to look at the converter. It was plugged. Replaced converter and it runs great.

I also know that this is an old post, but if anyone reads this in the future, please know that even though there appears to be good exhaust flow, you still may have a very dirty catalytic converter.

I also had a difference in temperature from the gauge on the dash, to the scanner temp. The scanner would read 186 and the gauge on the dash would go over 210. I figured out what was causing this. It was that the gauge sensor is located in the end of the cylinder head and the computer sensor is located in the block. The heads were getting hot due to the restricted exhaust.