liquidroam

LT1 trouble shooting help

So I had a race weekend at Hallett in OK. It ran great Friday morning. Midway through the session right after lunch I just started loosing power. At first I thought I was just not carrying enough corner speed and subsequently exiting at a lower RPM. It got worse fast though. We had noticed after session one that my water pump had started to leak from the weep hole so I planned on changing it that night. when I started loosing power I assumed that the Opti had gone bad from water getting inside or something.

Replaced those that night. Also the plug wires where on their last leg so went ahead and put news ones on as well. I checked all the spark plugs that night and gaped them. A few looked a bit too white but they did not correlate with the dead cylinders that I had.

On Saturday for warm up..... same problem.

We found out that the back three cylinders on the driver side were not doing anything. We determined this by pulling the injector plug on each cylinder one at a time and then replacing it to see if engine reacted. I know I had air because..... well I have no reason to think it would not be getting air. I know it had spark because after replacing the opti i pulled a spark out of one of the dead cylinders and had Tyler turn the car over. Shocking the crap out of myself confirmed that we had spark. Last but far from least I know that the injectors were at least firing because you could feel it and Tyler put a screw to each one and against his ear and could hear them. I at the time what I did not know is whether or not fuel was actually making it through. I ended up find out that Curtis had injectors in his trailer so i put those on. Still no fix.


Back here I ran a compression test. Every cylinder was between 125 and 135psi. Measured fuel pressure at idle with vacuum line pulled from the FPR, 42. With Vacuum line on and on the road, 34-38 WOT.

I am hopefully going to be pulling the codes this weekend, so hopefully that sheds some light. That being said, at this point if anyone has ideas I am all ears.

Injuneer

For more accurate help:

https://www.camaroz28.com/forums/lt1...nature-879835/

liquidroam

Touche...

Adding it to my signature, for here real fast though. It is a 95 car with a 95 engine but not the original engine. LT1 obviously, Manual. As far modifications go since the race series is meant to be budget we are not really allowed to do much to the motor. Dyno is 259hp and 310trq with a 38mm restriction.

Injuneer

34-38 PSI at WOT/max engine load (5,000+ RPM) is too low. Should be no lower than 40 PSI. You’re losing 10% of the required fuel flow at max power demand. But 42 PSI at idle (no vacuum) should be adequate to provide the required fuel.

Fuel enters at the back of the passenger side rail, and leaves through the fuel pressure regulator at the back of the driver side rail. At WOT, the last three cylinders on the driver side are taking the biggest hit. Not sure why that would also be the case at idle, where you identified the problem.

Never seen a case of an obstruction in the rails causing a problem, so hard to correlate the low pressure at idle to three cylinders not firing. Can you shoot the exhaust manifold temps with an infra-red temp gun, to verify non-combustion cylinders?

That's one of the reasons we need the year of the car.... a 93's batch fire injection is a significantly different configuration.

liquidroam

Hard to get a really good shot on the driver side due to more heat shielding but the highest I could get on those is 183 when we shot it at the a week ago. I will be working on it again on Sunday so I will shoot it again and report back. Another one of the guys on our AICMC forum mention the same thing today. I am going to run codes first and then pull the fuel rail, disconnect spark from the coil, zip tie baggies on the fuel injectors and turn it over to see what injectors I get fuel from.