I have a 1990 l98 with a 6-speed and 106,000 original miles on it. Here is a little history on this car...

Prior to us getting the car it had sat for 3 years without starting. Luckily it started and ran "okay" and even made the 30min ride home. I drove it for a few months until the fuel pump gave out. From there it sat for another 3 years until I could get around to working on it again. Over this summer I replaced the pump and screen, fuel filter and gave it a full tune up (plugs, wires, cap, rotor, PVC valve and air cleaner). It was running better but still not great. I bought a set of Bosch III injectors from FIC and installed those. While the engine was apart I cleaned the runners, plenum, throttle body and installed a new delco Egr valve.

The problem:
The car needs to turn over a bunch of times before it will start and then stumbles a bit until I hit the gas a couple times. Then when driving if I hit the gas hard between first and second there is a second or two of hesitation then it picks up and seems to run good. Under normmal driving conditions, there is a slight hesitation. It doesn't stall at an idle and has lots of power.

So far I have sprayed down the engine starting fluid looking for vacuum leaks which none were found, timing is set at 6 degrees BTC per the label, IAC measures at 1 1/8", TPS is set at .54 volts with throttle closed and 4.23 at WOT. I don't have any codes and yes the service engine light does work. I did have a code 14 or 13 (forget now) but replaced the sensor and that code is gone.

Any suggestions what to check next?

 

If you haven't yet, replace the 02 sensor. 6 years of no use can leave them ugly and rusty. Hook up a fuel pressure gauge and see if you are losing fuel pressure at start and idle. Maybe your regulator is shot. Those a 2 good places to start. Good luck. Willie

 

Thanks, it's definitely worth a shot....

 

Check TPS do search good luck

 

Was there something I missed on it? I did check the voltage with the throttle closed .54 and at WOT 4.23

 

Update....

Checked fuel pressure:
After sitting for a week: 0
Turned on key: 50 then dropped to 45 once pumped stopped
After 2 min (key off): 42 psi

Checked the system per the FSM
key on , then off and pinched pressure line, pressure slowly dropped.
Key on, then off and pinched return line, pressure slowly dropped again

FSM says its a leaking injector(s). These are brand new with less then 20 miles on them.... I will need to talk to FIC

Changed the O2 sensor, the old one was crud covered and looked a little deformed... Anyway, the car is running a lot better but not prefect.

Took the car for a ride and hit the gas hard between first nd second, fuel pressure dropped to 20 Psi and the car hesitated. Pressure climbed and the car started picking up again... Bad regulator maybe?.. Suggestions anyone?..

 

check and clean or replace the Idle Air Control Valve, located on the side of the throttle body; replacement isn't expensive; cleaning it (and the throttle body) is almost free. make sure you clean the passages leading to and from the IAC.

 

THanks for the suggestion... I have already cleaned and adjusted the IAC. I did speak to Jon @FIC and he had me clamp off the return line then turn the key on and check the PSI. I got 60 at first then it slowly started to drop...Looks like a bad regulator. Ordered a rebuild kit so we will see how that goes...