Car won't run, 1990 Chevy Corsica, 2.2L, throttle body injection, distributorless ignition.

Tiny
IRONMAN1959
  • MEMBER
  • 1990 CHEVROLET CORSICA
  • 175,000 MILES
Drove the car to work one day with no problems, it had been running fine up to that point. When I got off work 12 hours later car did not want to start, much longer cranking time than normal. Once it started it was idling very rough and then stalled. After 3rd or 4th attempt car started and seemed to be fine so I started down the road. Got less than a mile and car stalled out driving down the road. Had the car towed home, car does not want to start on it's own but will eventually. Car will start immediately with a brief shot of starting fluid in the throttle bottle. Once the car starts if you jockey the throttle from closed to any position the car seems fine as long as you rev-let off-rev-let off-rev-etc. If you try to let the car idle it dies within a few seconds, if you try to hold the throttle steady at any position it also dies almost immediately. As long as you jockey the throttle open/close/open it revs, slows and sounds fine. As soon as you try to idle or hold steady it dies. I thought I had a fuel delivery problem. This is a 1990 Chevy Corsica, 2.2L 4 cyl. With throttle body injection and distributorless ignition. The first thing I looked at was the air idle control valve, I removed it and started the car and it was moving in and out slightly so I assume it is fine, also the problem is not only at idle but at part open throttle as well (throughout the entire throttle range). I did however replace it with a junk yard unit. Next I replaced the fuel filter but no help. Next I installed a brand new injector in the throttle body, still no help. Dropped the fuel tank and replaced the fuel pump, no help. I then disassembled the throttle body regulator assembly and the diaphragm and spring appeared fine. I got a fuel pressure tester and have 12 PSI pretty steady at the throttle body inlet. I have removed and plugged each vacuum port from the intake manifold one at a time and found no difference. The only other possible vacuum leak would be the intake gasket which was replaced 5000 miles ago along with the head gasket and exhaust manifold gasket and new spark plugs. Or the throttle body gasket, but I have read that a vacuum leak would not be very noticeable with open throttle and I don't hear a leak. Plus the car accelerates fine, it's holding the throttle steady that causes the stall. I have checked the throttle position sensor output voltage it's.665VDC at closed throttle and increases smoothly through the open throttle range to around 4.5VDC which is slightly low at the high end but smooth throughout the range. I also checked the MAP sensor voltage with key on while sucking on the vacuum port and it starts around 5VDC and drops to about 1VDC and is smooth and drops as more suction is applied. The only OBD code displayed was a 23 which indicated a intake air temperature fault but at that time the breather was removed and the sensor unplugged. When I re-installed the breather and plugged the sensor in the code went away with no other codes present. I have tried running the car with the O2 sensor unplugged because I read that it would go into open loop mode without the sensor input and it made no difference, plus I don't think the O2 sensor would prevent the car from running would it? I did not do specific diagnostics on the crank position sensor as it is very hard to get to. I did buy a ignition tester (the type that goes in series between the plug & plug wire) and I see relatively slow sparking during cranking with a steady bright red continuous spark once it starts, the coil packs and wires were replaced about 4 years ago (50,000 miles?). The best I can tell is the fire is OK and I've read that if the firing looks good the crank sensor is working OK. My only other thought is to replace the ECM but it is fairly expensive especially if it does not help. I don't know what else to check, any help would be greatly appreciated.
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Saturday, May 18th, 2013 AT 6:38 PM

9 Replies

Tiny
HMAC300
  • EXPERT
Scan for codes and check fuelpressure 41-47 psi if low replace pump
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Sunday, May 19th, 2013 AT 8:07 AM
Tiny
IRONMAN1959
  • MEMBER
I have replaced the filter, pump and injector. Pressure is 12 PSI and everything I've read online says 8-12 PSI for throttle body injection.
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Sunday, May 19th, 2013 AT 8:16 AM
Tiny
IRONMAN1959
  • MEMBER
Also I have checked for codes and there are none.
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Sunday, May 19th, 2013 AT 8:16 AM
Tiny
HMAC300
  • EXPERT
Check resistance of crank sensor it can be bad and not give a code. I don't have any specs on what it should be so you may have to check against a new one. Have your ignitin module checked, I think auto parts can do that yet.
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Sunday, May 19th, 2013 AT 10:34 AM
Tiny
IRONMAN1959
  • MEMBER
Today I unplugged the vacuum line from the MAP sensor and now the car will run but sputters while driving. If I close off the hose for the Map sensor the car dies but if I allow it to have a small vacuum leak there it will run. Idles pretty good that way and revs OK in park but sputters some going down the road. Gives me a code 45 for high MAP sensor signal voltage which makes sense because the voltage decreases from 5 volts as vacuum is applied. If I unplug the electrical connector from the MAP it dies. This problem makes no sense to me. But sense it's running now I suspect the crank sensor and ignition circuits are OK. The way I discovered this was I took the throttle body off and cleaned it some, when I re-installed it I forgot to plug the MAP sensor vacuum line back in, the car started better and idles and runs.
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Sunday, May 19th, 2013 AT 4:15 PM
Tiny
HMAC300
  • EXPERT
Check for a vacuum leak, when you unplug the vacuum you put the car into open loop and it runs rich. The code 45 would come on because you have unplugged the sensor. Check the wires on top of the tbi unit for making good contact. I stil think you should get the ignition module checked as well. Clear the computer then see what happens and see ifyou get any codes instead of blindly guessing this or that which you have done enough of already.
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Sunday, May 19th, 2013 AT 6:28 PM
Tiny
IRONMAN1959
  • MEMBER
I've got good spark on all 4 plugs, if I disconnect the plug wires one at a time the engine runs rougher so it appears all cylinders are firing. I've connected a vacuum gauge and it has around 18-20 inches of mercury which I have read is about right but it does flutter a bit between 18 and 20 which I've read indicates a misfire or a compression issue. What I don't understand is why it dies if I plug the vacuum to the MAP sensor back up. The sensors voltage readings appear normal, it acts as though the computer is riching the mixture flooding the car because after it dies it takes a minute to start like it sputters some then starts like it's got too much fuel in the intake.
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Sunday, May 26th, 2013 AT 5:14 PM
Tiny
HMAC300
  • EXPERT
I'm sending a flow chartfor code 45 onhow to diagnose it as it cold be the ecm. Ckt 412 means to unhook the O2 connection as it leads back to ecm. However also check resistance of crank sensor and cam sensor. Also if you can have your ignition module checked as this supplies voltage for tbi. And check ground at engine block and battery to body.
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Monday, May 27th, 2013 AT 5:48 AM
Tiny
IRONMAN1959
  • MEMBER
I have replaced the ECM with one from a salvage yard. This has fixed the issue.
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Sunday, June 23rd, 2013 AT 12:21 PM

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