Starts OK, does not idle, just dies.
OK I gave my 1989 Vette a tune up (plugs, distributor cap and rotor). Worked great. I had a leaky injector(s) so I replaced all of the fuel injectors with ACCEL. Fixed the leak. It starts, shakes like crazy, and then dies immediately. If I press the gas petal a little the tach jumps up to 3k. So far I have replaced the IAC valve and the TPS. I haven't adjusted the TPS yet but the symptoms haven't changed. I am running out of things to change. I do not have a scanner.
Joe.....check your IAC and TPS for being set right.....then look at your plug wires, making sure they are routed correctly.....its easy to get them mixed up if your not careful.....I'm guessing it was running Ok before you changed the cap and rotor, so off hand I think you might have put the plug wires on the wrong terminals on the dist.....it happens.....check them out really good first.....Bill
Since it is the shortest day of the year today this should be easy to do . Find a dark spot and with the engine running raise the hood. Now watch for the light show. If the wires are misrouted or on the wrong terminal they should be arcing. Generally if it was running alright before and it s not now then look at what you touched etc. Another thing to check for with the hood up and running is the plugs. Some of them are hard to put in and if dropped. The porcelain could be cracked (don't ask how I know this)
Not a spark plug/wiring problem.
Sorry guys. After I replaced the cap, rotor, and spark plugs I test drove the car. Everything was fine. It ran better than ever.
Originally Posted by John Robinson
I then replaced all of the fuel injectors since one or more of them were leaking. The original/old have 25 marked on them. The new ones are 24 Lbs. per hour ACCEL. I had to replace the idle air control valve since I soaked the old one with break cleaner which totally ruined it. I did a resistance check of the throttle position sensor which showed values a lot different from the values I found on the web for a 1985 vette so I replaced it as well. I set the IACV to about 26 mm, just short of the 28 spec. I haven't set the TPS yet.
I removed the battery to clear the ECU.
I start the engine. It bucks and runs rough and never idles. It just dies.
I then press down on the gas petal a little and try starting it again. It runs but then jumps up to 3000 rpm.
I am the 2nd owner and the car has been modified from factory with 25 Lbs/hour injectors (replaced with 24), there was some sort of box in line with the TPS with a green LED. The LED is on when the TPS is disconnected. I have removed it. No other markings were on the box.
The engine trouble light blinks code 12 telling me everything is OK.
I suspect a "performance" ROM/chip has been added but don't know for sure.
With all the wire connectors being pulled off and put back on the sensors you may have broken a wire. The wires have a habit of getting old and brittle with age. Take and follow the wires from the TPS back into the wiring harness. You will find were the ground wire goes into a bundle of ground wires from the IAC,MAP/MAF and water pump temperature sensor. Do a continuity check from that ground bundle on each wire to the connector. While doing the continuity unplug the connectors from the ECM so you don't back probe the ECM with your voltage tester battery. Also while testing continuity wiggle the wires to see if the continuity fails to show on your meter.
Scan tool results
OK I managed to find a scan tool. With the key turned on and the engine off I get the following results:
Originally Posted by John Robinson
PROM ID 3491
coolant temp 77.4 F
startup coolant temp 76.1 F
* TPS = 0.58 volts (this varies as I rotate the sensor plus it's a new sensor. The spec calls for +/- 0.08 volts)
engine RPM = 0
vehicle speed = 0
O2 sensor = 0.408 volts
O2 cross cont = 0
block learn = 128
block learn cell = 0
integrator = 128
* idle air motor position = 160 (is this fully closed?)
* desired idle = 3187 RPM (why is this so high?? )
engine load = 0
manifold temp = 71.6 F
EGR duty cycle = 0%
CCP duty cycle = 0%
battery = 11.9 V
fuel pump sense = 0 volts
spark advance = 0 degree
knock sensor = 0
knock retard = 0%
integrator pulse = 0
engine not running
MAP sensor = 1.6 volts
MAF = 23 gr seconds
battery voltage high = no
shift light = off
AC not requested
park neutral detected
AC clutch disabled
O2 sensor not ready
1st gear engaged
So it looks like everything is working except the IAC (set to 160 counts) and the desired idle of 3187 RPM. This could be why it jumps up to over 3000 RPM when I give it a little gas. How do I rest this number to 1000 RPM?
The scanner is also showing code 22, voltage too low. This may be because I just adjusted the TPS to 0.58 volts and haven't cleared the codes yet.
I think that the voltage to low is the battery, 11.9v seems low to me. It should be around 14v.
Last edited by jimbil208; 12-21-12 at 07:15 PM.
Reason: correct spelling
I agree the battery voltage is to low. A funny thing about the electrical system on these C4 Vettes is that a low battery confuses the ECM and it goes crazy trying to compensate. I first noticed this with a BMW motorcycle that had the Bosch ignition. You might wonder why I mention that but it is because the ignition system is the same on both. GM used the Bosch ignition on the C4. For some reason that system requires the voltage to be above 13 volts and when the battery starts to go bad it will announce itself with a bad running car. So check the voltage from the alternator to be sure it is working. If the alternator is good then replace the battery. Oh I almost forgot check to make sure the ground cable is tight on the battery that also could contribute to the low voltage.
- Online Member
13.6 V is normal for a running engine. My vette has the key on but the engine off when I did the scan so 11.9 is normal for a battery.
Originally Posted by John Robinson
- Online Member
Ok I just went out and checked my voltage with the key on and the engine off. My digital reading was 11.7volts. Now here is another critical test. Watch the voltage when you go to start the car. On mine just know it did not drop off 11.7 with the engine cranking to start. If the voltage drops below 10.5 then you have a bad battery or ground or a low battery not being charged fully. All of which will make the car run badly. If you don't have a digital meter for voltage then here is what I suggest. Go to Radio Shack and get a cigar lighter auxillary plug and hook it up to the voltmeter so you can read what the system is getting for voltage while running. In reality what you will have is a digital voltage gauge hooked into real time information. Buy the way this picture was taken with the key on engine off.
Code 22 is NOT about battery voltage. Its about the TPS reference voltage.
TPS gets 5V as reference from the ECM. How much of that returns tells the ECM where the throttle is.
When the voltage is too low the fuel is not adjusted to throttle position...
Code 22 sets when there is a break in the dk blu or the grey wire or when they are shorted.
Check the ranging of the TPS with the DVM.
Check the 5v reference signal in the gry wire. Check for the return signal in the dk blu wire (plugged in moving throttle manually)
Check TPS harness with the DVM and move harness sections around to find a wire broken internally.
Confirm fuel pressure of 40 at key on. Just under 40 at idle, if it will.
Never screw with a new IAC. Just measure it according to the FSM guide, and if it falls within that spec screw it in and forget it. Most IACs get ruined by trying to force the pintle to turn the wrong way. It WILL set itself when the engine starts. Thats what it does...it adjust itself.
Boomdriver is right about the code 22. Unless I am missing something the readings the op has posted show the voltage at 11.9 volts for the battery and then a second issue is a stored code 22. As Boomdriver and I have said the wiring is the what needs to be checked before anything else is done. I am providing a copy of a Code 22 diagnostic sheet from my 93 manual but I think it may have some helpful information for the op to understand what we are saying.
Note what the manual says about the importance of the TPS and how it works with the ECM being able to learn what the TPS voltage is and then program itself as long as the voltage from the tps is within range. Now what Boomdriver and I have learned is that the grounds control the ECM. You would think that the computer would be looking at the voltage into a sensor but in fact it has to look at the ground voltage to determine what each sensor is doing. From that it then makes adjustments to the fuel delivery the timing etc in order to control the engine . Now if the signal to the ECM is broken with a bad wire then the ECM says the TPS or IAC or whatever is bad because it only knows that it is not getting the correct information from that circuit. Boomdriver and I have been down this road many times with bad wiring. What I have found that helps is to carefully check the wires and connectors to be sure they are not damaged from age and being handled. When I put the connectors back together I use dielectric grease on them to make sure they get good contact and also to seal them against moisture and corrosion.
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