help quick won't start
Instructor
Joined: Jul 2007
Posts: 174
Likes: 0
From: Toronto Ontario
posible vacuum leak?
If the MAP sensor sees close to atmosphere the injectors will probably inject more fuel than needed. Hook up a vacuum gage to the plenum and crank her over without putting your foot down on the gas ( throttle valve closed ). You should have a good strong reading approx 15-20in Hg. Also check to make sure your TPS is working properly. (0.45 volts at closed throttle, gradually opening throttle to WOT you should see a steady climb of voltage to ~5 volts. Any fluctuation in voltage reading while doing this means TPS is bad and needs replacing). Also MAP sensors can go bad by sending incorrect readings to the ECM. Also 5 volt supply to TPS and MAP sensors could be out of specs ( something lower or higher voltage) throwing the ECM off. The coolant sensor is there to give the ECM a base idle speed ( colder engines rev higher at idle than warmer). So, to recap, check all vacuum hoses to make sure you don't have a leak, check TPS voltage (the sense voltage), check 5 volt supply voltage to TPS and MAP and check sense voltage of MAP ( i'm not sure what it's supposed to be, check FSM).
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
A few things that come to mind. You mentioned the new spark plug tips are black/carboned. You could have weak spark. Make sure that you are getting atleast 1/2" spark on all 8. The fuel pressure seems to hold adequately enough. As long as the fuel pump is working properly, the fuel pressure will not drop off when cranking. Have you made sure the air passages are not blocked and the IAC is working? The IAC could be stuck closed and not letting air into the intake and causing you to have to hold the throttle open to supply enough air.
You apparently have a very rich condition gettin too much fuel, not enough air, or not enough spark. 24# injectors should not matter in this situation. The engine should still run on it's own and if anything just run rich, if that. The ECM is also a likely suspect. It would be nice if you had a spare to swap out, just to use as a troubleshooting tool. Do you know anyone around you with a 90 or 91 that would be willing to let you try?
If the timing was way off, it would cause a similar problem.
You apparently have a very rich condition gettin too much fuel, not enough air, or not enough spark. 24# injectors should not matter in this situation. The engine should still run on it's own and if anything just run rich, if that. The ECM is also a likely suspect. It would be nice if you had a spare to swap out, just to use as a troubleshooting tool. Do you know anyone around you with a 90 or 91 that would be willing to let you try?
If the timing was way off, it would cause a similar problem.
Melting Slicks
Joined: Feb 2003
Posts: 2,642
Likes: 800
From: Saskatoon Sask.
I don't know if the L98 coolant temperature sensor works the same as an LT1, but I just experienced the exact same symptoms on my 92. It turned out to be a faulty sensor. The coolant temperature sensor is just a thermistor which changes resistance with a change in temperature. In my FSM, it shows a chart of the resistance values that correspond to a specific temperature. I unplugged the sensor and placed a 3000 ohm resistor(which corresponds to an ambient temperature of approx. 72*) across the harness terminals and it fired right up. As the temperature of the engine increased, it began to run rough again so I replaced the resistor with a lower value one and it again ran smooth. With a faulty sensor, it was telling the ECM that it was in excess of -40* and the ECM was telling the injectors to supply too much fuel. Might be worth a try.
7th Gear
Joined: Apr 2007
Posts: 7
Likes: 0
From: SAUGUS MASSACHUSETTS
I had similar problem just not as bad . I replaced the ecu with the one from the junkyard ,it is a real common one i think mine came from a lumina $30 i just swapped out the prom. The car got better but still has a glitch . cheap fix if not peace of mind ruling out the ecu
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Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
Ok here goes I tested a bunch of stuff under the hood today and maybe this will help you help me Battery 12.01 (not running) 4.67 volts to Coolant sensor 5.03 volts to MAP sensor Throttle Position sensor 0.551 (closed) then when I opened the Throttle all the way it was a steady climb to 4.36 volts Thats about all I could test. I still need to get a vacum gage and test that. THANKS AGAIN GUY'S YOU ARE A BIG HELP IN DIAGNOSING THIS PROBLEM. 
Pipe
Pipe
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
I also tested the IAC and it was within the parameters. Im testing the sensors with the Mid America kit that has all the test connectors with the pigtails to use the volt/ohm meter with it. THANKS AGAIN Pipe
Instructor
Joined: Jul 2007
Posts: 174
Likes: 0
From: Toronto Ontario
Coolant temp Is resistance measured
You have to measure the resistance coming off the coolant sensor to check to see if it's any good (voltage doesn't help on this sensor). Here's a table of resistance versus temp on good coolant sensors.
degrees F | Ohms
------------------------------------
210 | 185
160 | 450
100 | 1,600
70 | 3,400
40 | 7,500
20 | 13,500
0 | 25,000
Take sensor out of vette, put in a small pot with water on the stove. Stick thermometer in pot. Attach ohmmeter to terminals of coolant sensor. Turn on stove and note the resistance readings versus temp. If they don't match to the table above( within 5% tolerence ), discard sensor and buy new sensor, do same test as above to make sure it works ( otherwise return sensor and get money back!), put in vette and then everything should work.
degrees F | Ohms
------------------------------------
210 | 185
160 | 450
100 | 1,600
70 | 3,400
40 | 7,500
20 | 13,500
0 | 25,000
Take sensor out of vette, put in a small pot with water on the stove. Stick thermometer in pot. Attach ohmmeter to terminals of coolant sensor. Turn on stove and note the resistance readings versus temp. If they don't match to the table above( within 5% tolerence ), discard sensor and buy new sensor, do same test as above to make sure it works ( otherwise return sensor and get money back!), put in vette and then everything should work.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 7
From: Tampa Florida
Gas May Be No Good / Contaminated!
"Car was really hard to start and smoking like crazy" before you changed the injectors?
If all is well drain the fuel in the tank, drain the fuel rails, lines and change the fuel filter....then add "new" gas.
Good luck!
If all is well drain the fuel in the tank, drain the fuel rails, lines and change the fuel filter....then add "new" gas.
Good luck!
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
The sensors seem to check ok unless i'm checkin em wrong. I took a plug out (black sooty) and connected it to the plug wire and it seems to have constant steady blueish white spark when I cranked it over. I still had to hold my foot to the floor to get it started. Still had smoke from the exhaust (gassy smell ) seemed the longer it ran and the warmer it got the better it got. The idle seemed to smooth out and it stayed running when I took my foot off the pedal. When I went to jump on the throttle it stalled right away and then wouldn't start again till I put my foot to the floor. Pipe COULD BE THE ECM 
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
No I didn't hook a noid light to the injectors. The car has no cats on it. Long tube headers and good muffs. A friend is going to try and help me get a TECH #1 scanner from a GM mechanic he knows. What will the TECH 1 tell me and is it hard to operate? I'm going to remove the IAC and clean it and make sure it's seating right in the TB THANKS AGAIN Pipe
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
Trackman 44 help me here man. I went up to Radio Shack and got a 3300 ohm resistor cause they didn't have a 3000 I unplugged the connector from the coolant temp sensor and jumped the resistor across the harness terminals. It started right up without putting my foot to the floor to start it. I let it run for about 10 to 15 min. like this with the resistor jumped across the connector. When I went to jump on the throttle after it was warm it stalled. Pipe THANK YOU GUY'S
THANK YOU GUY'S