Fuzzman17

Anyone have an idea what would cause a stock 305ci 92 RS to flood sometimes when it starts? It's never done it when the engine is the least bit warm only if the car has been sitting for 12 hrs. or more. When first started it will fire and die. when this happens the only way to start the car is to give it about 1/4 throttle. You can tell it's loaded up with fuel.
The other thing I have noticed is a split second hesitation when accelerating from a stop when cold. also the throttle seems less responsive sometimes when cold than others in the low RPM range. (less than 1500)

Things I have done to the motor include, Plugs, wires, Changed 1 injector, (the other is about 1-2 years old) Air filter, O2 sensor, IAC, Set the timing, Set the idle speed. B-12 fuel system cleaner in the tank, ran Seafoam thru the engine, Checked TPS voltage.

Engine generally runs well and pulls strong to the shift points. Last owner had changed the cap and rotor 2-3 months before I got the car and the fuel pump about 1 year before. O2 cross counts look good. Engine pulls about 30 kpa @ idle. Idle will vary +/- 25 RPM in park.

One other thing, the emissions test shows a momentary spike in HC (1.20-1.45) when accelerating. Tech said it could be caused by a slight misfire and that the cat is weak. The car was staying in open loop till I changed the O2 sensor. I was told this was the likely cause of the cat. going bad but the car gave the same emissions readings before the O2 sensor was changed.

Anyone have an Idea what I should check next???

JaybirdLSSU

Sub'd to follow along, I'm having the same issue with my truck (91 K1500 5.7). I've replaced everything you have such as the plugs, wires, cap, rotor, fuel filter, and O2 sensor. I also replaced the coolant temp sensor as someone on fullsizechevy mentioned that when they go bad they read a colder temp than what the coolant actually is. Still no help, I have to crack the throttle in the morning to get the engine to fire but the rest of the time it runs great. I've made sure that there are no vacuum leaks or broken wires in the harness multiple times. My next step is a new pair of injectors as mine are still the factory originals with 200,000+ miles on them. I may also replace the MAP sensor.

Fuzzman17

I'm wondering if the problem isn't my TPS.

https://www.thirdgen.org/tpimod2

Maybe an intermittent problem that I haven't caught with the scanner yet.

Fuzzman17

Found a converter and it would seem that 30 kpa is about 8 in hg. I think there is a problem with my map sensor.

bcmag

if this is ahigh mile engine very carefully check vacuum port at tbody where map sensor hose attaches.have seen these plug up w/carbon which causes low readings and also acts as a sort of check valve on acceleration.....drop in vacuum signal to map on accel is delayed due restriction in port.good news is every time ive seen a couple good squirts of carb cleaner into port in tbody usually clears it right up.or take it off and clean it out...tbody gasket will eventually fail if it hasnt already been replaced.

Fuzzman17

bcmag, thanks for the heads up on the vacuum port. I'll check it out tomorrow if it quits raining.

Fuzzman17

OK, I changed the TB base gasket, Cleaned the vacuum ports, Tried a different map sensor, did a voltage drop test on the MAP ground, Checked the voltage in and out of the MAP, and compared voltage out of the MAP with what my scanner says. There was less than 0.05 difference.

Reading with engine off 99.65 kpa. I'm less than 1000 ft above sea level 43* day seems OK. Vacuum gauge shows 17 to 18 in hg @ MAP sensor. 2nd MAP sensor was a different P/N than the one on the car but they read the same.

1.20 VDC = 32.86 kpa engine @ idle.
4.74 VDC = 99.65 kpa. engine off. VOM read 4.78
Voltage drop 0.01 @ idle, 0.08 Engine off on the ground wire.

I'm thinking either the wrong map sensor or a bad ECM.
Right now I'm leaning toward a bad ECM. (had problem with the ECM running the battery down that just went away by itself.)
Can anyone else think of anything else I should check before I change the ECM?

Fuzzman17

Did some research last night on MAP sensors. looks like the ECM might not be the problem. Back to having the wrong MAP sensor. have to let all I learned soak into my brain for a bit. and get my vacuum pump fixed.

bcmag

dont forget map is not a representation of actul engine vacuum .it a measuremuent between atmospheris press. and negative press. of engine .example baro=29 intake vacuum=18 in. map reading on scanner =11 in.

Fuzzman17

Yeah, I remembered that while I was in the driveway trying to figure out why the kpa reading was the inverse of the vacuum reading. I guess 2 of those rusty old brain cells finally made contact "Manifold ABSOLUTE Pressure". Duh. That's the difference between the baro. and the MAP sensor.

Well at least the map sensor has been checked out within an inch of it's life. LOL

The thing that had me screwed up was that I remembered reading the MAP should read at least 50 kpa but I think the reference was to a baro sensor.

Things left to check: Ign module, coil, and ESC.
Things to double check: Timing, Plug Wires.

Thanks for the reminder bcmag.

Fuzzman17

Pulled the dissy because a screw broke off in it when I tried to pull the cap. Removed the screw, regreased the module, (it was beyond dry) checked the bushings, put dissy back in with new cap and rotor and my problems seem to have gone away. Still took a new cat and 2 gallons of E85 to squeak by the emissions test.

Folks at the test center said that Camaros and Fire Birds have trouble passing. That seems odd to me. My friend that is a cert. GM mechanic had to take one the same as mine 18 times to get it to pass. Only in Indiana.