Hey folks,

strange problem here since 2 months: My car (1988 Firebird Formula 305 tpi) has got rpm drop at cold start.
When I turn the key and start the car, it fires right up and spins to about 1100 rpm, then it drops to ~500/600 for about 3 seconds, meanwhile it sounds like I´ve got an aftermarket camshaft in it, but I haven`t. After that few seconds the engine comes back to normal cold idle speed (1000-1200 rpm depends on the wheather).
To just notice, the car otherwise runs perfectly fine! No codes, no stumble, nothing. Very good gas mileage and strong for how it is till now.

I have the 9th injector, could that beast cause that kind of issues, is that a known problem?

Greetings,

Chris

 

Do you have any means of using a "Scan Tool" either Laptop & Cable or Professional Scan Tool? Monitored startup voltages, pressures, etc? Done any random troubleshooting like checking condition of ignition components or cleaning the throttle body & iac? Just bouncing ideas until an expert chimes in,

 

I had a similar problem, the surging idle is usually a vacuum leak. But as stated above be sure to clean the IAC and definitely check your pcv and ccv vacuum lines. I don't know about what the usual idle for tpi motors are but Mine usually starts at around 1100-1000 and then lowers after a couple of seconds goes down to a steady idle around 500-450 rpm.

 

Also, do you know if that cold start injector has ever been replaced? Unplug that injector and see if that solves the problem. If that fixes it then you found your problem especially if your problem is only at cold start

 

Hey guys! Thanks very much for your answers!

Today I disconnected the cold start injector plug and tested it. It now needs to crank 1 or 2 times longer but will start and idle at the same speed, 1050 rpm this morning. No drop in RPM. I will check this the next days and see what happens.
Also I have tested the fuel pressure, could you guys take a look at the values please?

Fuel pressure, engine cold but running and idling at 900 rpm:
with vacuum 42psi, without 32 psi. It drops slightly to 29-30 psi when I give it gas (2000rpm). After let of the gas it goes steady to 32 psi. After engine shut off it goes up to 36-38 psi after waiting 5 minutes. Again, car runs fine, just has got high INT values (148 was the highest) when go WOT.

Shouldn´t the pressure be higher?? Also how much times should it takes till it drops in pressure?
Fuel filter has been replaced recently.

Greetings,

Chris

 

Heyho,

I want to attach some more infos:
Today I measured the fuel pressure again while clamping off the return line and the pressure increased well over 50 psi.
So my fuel pressure regulator is dead and I will buy a new one. I thought about the Holley AFPR.
Maybe my cold start will be better then also.

 

The Holley is expensive but nice, I have it on my L98 and it’s design is the best out there IMO. The adjustment dial can be turned by hand, no jamming a wrench under there every time you want to make an adjustment and no worry of it not having enough clearance with the plenum.

 

Another idea with the cold start is just get the 9th injector delete kit and have a PROM burned with the 89’ start up sequence. Many tuners can do that easily and a good opportunity to program the fans to come on earlier to have the car run cooler or eliminate VATS before it causes problems. Tuned performance did mine and it was a nice improvement over the stock one, woke the car up just a touch with much better cold starts and a cooler running engine.