I just installed a TPIS Big Mouth intake and SLP Runners with Ported plenum. The SLP Runners were '89 and later models (without coldstart inj)
This was all installed on my '86 Vette. I changed out the '86 fuel rails with '89 fuel rails. I also installed a factory '89 Prom.

My car has a hard start and will not idle. The engine is running really hot and the exhaust manifolds are getting cherry red. My car will not start without pressing the throttle and holding above 1200 RPM.

I have checked the cranking compression in 6 cylinders and all were 170 psi. I have checked fuel pressure and it is around 44 psi and held at 30 psi overnight. I have also check vacum which is low (around 10 lbs @ 1000 rpm). This has me concerned because it use to be around 19 Lbs @ idle.
I sprayed engine start around the runners and throttle body and found no vacum leaks. I've check and I have no vacum lines disconnected. I set timing @ 6* with the EST disconnected.

I'm at a lose I don't know what else to check. Could it be I need a new Prom burned? I have a mild cam installed, with a catback, free mods, K&N, roller rockers (stock ratio). These were inplace before the TPIS intake, runners, were installed and the car ran fine with the stock prom.
Last thing I have no stored error codes.

Please help. TIA

 

10" vacuum is too low. You may have had a gasket slip or something. It could be leaking on the underside. I would say you need to find the leak even if you have to start taking it back apart .

 

Something ia wrong. My 87 has factory programming and does not have issues. My combo is waaay different from stock. The cherry red manifolds suggest timing, but you verified it is not. Is it possible that the outer ring on the balancer has slipped? If so you are not where you think you are regarding timing. I would check this closely. This could cause the problems you describe. Whenever I install a new balancer, I scribe a mark from the inner hub to the outer, this way I can do a visual inspection from time to time.

 

I didn't verify the timing my neighbor did and I'm not sure he was familiar with the timing marks on my car. I know when I was moving the distributor it started sounding better, but he said I was going the wrongway. I got tired of working on my car and had to just walk away before I got too frustrated. I agree it sounds like timing.

Keep in mind my car was running fine before I started this project.

I hope this TPIS and SLP combo is worth it.

Thanks

 

I did a cylinder head gasket on mine a few weeks ago and when i got it all put back together, it was idling really really high, had low vacuum, and running really hot.
I was really worried one of the gaskets was leaking. I used the propane test but i didn't even increase the idle speed even when i let it suck some right into the throttle body. For some reason my engine seemed immune to the propane test.
Anyway, in desperation, i reset the computer, as well as did the IAC reset procedure.
One of those 2 things fixed it and brought the idle right back down to where it should be.
I dunno... might be worth a shot.

 

Since you suspect timing, verify that the dist is installed correctly.

If ok, it sounds like you will need to start taking things off till you find the errant intake gasket.

 

Thanks for the help. The timing was off, it was way off. I personally verified it and it is at 6* with the EST disconnected. The problem is it will not idle. I suspect its the IAC. I'm going to check that next and cross my fingers.

 

Test drove the car and it seems to run pretty good. Total Knock counts were 12 for the entire test run. I use to get a false knock. At WOT I was seeing 7* knock retard. Is this normal? 0* knock retard cruising around.
Also car is running lean. Thanks everyone for the help.

 

While back ago. My LT1 will not idle found out that the intake gasket was bad (brand new felpro gasket very thin bought from local auto part store) causing major vaccum leaks. I put in brand new GM gasket problem solved

 

Check the timing. If the timing is retarded too much, the air/fuel is not burned in the cylinder, and is burning in the manifold (I know this one!) . Disconnect the timing wire (brown), set initial timing at 6 degrees BTDC, that should do it. Set the timing

 

Checked for vacuum and it is between 18-19 lbs at idle. Timing is set at 6* with EST disconnected.

NEW PROBLEM: Car wants to try and idle at 450-500 RPM. I reset the IAC and the trottle screw is screwed all of the way out. My car use to idle around 650-700 RPM. Car will idle around 600 RPM when its warm, but not cold.

Does this sound like I need to have a new PROM burned to tell the IAC to idle higher. I should mention I'm using a factory '89 PROM in my '86. I converted to '89 fuel rails and got rid of the cold start injector. TIA