I’ve got a 1999 3.8 manual Camaro. I've posted a few threads so far about my ongoing problem in which I get random misfire errors. So far I’ve changed the fuel filter, air filter, cleaned the air intake manifold, replaced spark plugs, spark plug wires, checked the coil packs and ICM, taken off the fuel rail and cleaned out the injectors which seem to have gotten my car running great but I’m worried about the low fuel pressure. Has anyone had this problem? The pressure should be around 49 - 55 but my car is around 42. Is this enough to cause concern?

 

At what point have you measured the pressure? Is this with the key in ON, but not car not started? Or is this while it is running?

 

Measure with key On engine off, or run the engine, disconnect the vacuum line from the fuel pessure regulator, either will give you the actual fuel pressure from the pump.

 

I fallowed the manual and checked the pressure while the key was on engine off. The pressure in that position was 42 psi, the book says it should be between 49-55. While the engine is running the pressure is the same, the book says it should be 3 to 10 psi lower.

 

If it is the same while running, then it looks fine, according to the book. Which book are you referring to?

 

The book I’m referring to is the Haynes repair manual; what book are you talking about? The book says in chapter 4 section 2 " Start the engine and let it idle at normal operating temperature. The pressure should be lower by 3 to 10 psi. If all the pressure readings are within the limits" (49 - 55) "the system is operating properly" my pressure is lower than spec in both positions by 7 psi.

 

Are you setting a code for misfire? There is really no way to 100% test a coil. I have seen coils past every test but still be the problem. But as a rule normally coils fail when the spark is at its highest load. Which mean when the cylinder is under the most pressure. Hvy load low RPMs. As a general rule high RPM misses come from the primary ignition side (crank sensor/spark modual) or a lean condition. Since a motor need more gas at higher RPMs a fuel volume/pressure issue will show up at higher RPMs.

If you had a way to see what the O2 sensor could see while it was missing it would be easy to figure out. If the system was showing lean then rich when the engine missed it would be a fuel problem if it showed normal then rich then its a spark thing.

 

I was referring to what your book says. 49-10=39. 42>39. That's why I said it seems fine. As for why it is the same with the engine off, and when it is at idle, I'm not sure. I have the same book by the way, not sure why it changed after '98.

 

OK so it’s been a few months and I can officially say I have troubleshooted and fixed the random misfire / cylinder #2 misfire problem! It was caused by a spark plug wire lying over the #2 fuel injector wires. This caused a short Circuit flooding the number 2 cylinder with fuel at the wrong time causing a rich burn and misfire. It’s really my fault for not putting the spark plug wires back in they're proper location after replacing them myself. Also I had to replace the Ignition Control Unit because I didn’t know THANKS TO THE F****** HAYNES REPAIR MANUAL that the ICU is "glued" together with thermal grease to the steel heat sink it sits on and when I took them apart I weakened the heat dissipation properties of the heat sink causing premature death of the ICU (cost me $135.00). In recap if you have a random misfire or cylinder misfire check to make sure the spark plug wires are not laying over any other wires please. And if you want to check the ICU make sure you clean the surfaces of both the ICU and the heat sink and bond them together with thermal grease before reinstalling them. Also if you suspect the ICU most auto part stores can diagnose it for you for free but make sure you call ahead and ask if they're machine works for the Camaro. I REALLY HOPE THIS THREAD HELPS A FEW PEOPLE AND GOOD LUCK!

 

i had the same problem with my 97 3.8 liter. Plug the fuel pressure tester into the fuel rail on the left side as your facing the engine i believe while the car is running. It should be about 50psi. If its lower than that its usually either a bad fuel pressure regulator or a fuel pump. The fuel pressure regulator is much cheaper and easier to replace. To test if its the regulator disconnect the vacuum hose from it.(the regulator should be located in the back part of the fuel rail on the right side of the motor). after disconnecting the fuel prssure regulator vacuum hose if the psi drops i believe that means the regulator is good. If the pressure stays the same that means the fuel pump is bad. In my case the fuel pump needed to be replaced.