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Won't Start

Joined
Nov 9, 2003
Messages
19
Location
North Dakota
Corvette
1990 Black Coupe, 1977 Black Coupe
My '90 started immediately before but the other day it wouldn't start at all. I checked the spark and that looked good so I took the air intake hose off the fuel injection and squirted in some gas. It started right away and ran until I shut it off. Tried starting it again and it wouldn't start. Squirted gas in and it started immediately. Any guesses on what the problem could be?
 

68Roadster

Well-known member
Joined
Dec 16, 2002
Messages
1,040
Location
Dallas, TX
Corvette
'68 White Vert '05 Silverado SS
Long time since I owned a C4 but let me ask this:
Does it turn over but just won't light off?
Check your fuel pump relay (guessing it has electric pump), my truck did this and fuel pump relay was burnt. Swapped it out and it fired right up.
Just guessin' bud, hope you get it fixed pronto.
 

RonnieH

Well-known member
Joined
Sep 3, 2002
Messages
85
Location
Henrico, NC
Corvette
2012 Crystal Red Metallic
I'm sure others with much more experience will weigh in on this one, but given the information you'll have to start a logical troubleshooting process. About a year ago, my '90 would start immediately, and run for a few seconds and acted like it ran out of gas. After letting it sit for about 10-15 minutes, this sometimes repeated itself and sometimes started right back up. I went thru the whole troubleshooting list - checked fuel pump pressure - both at the fuel pump discharge and at the fuel rails, changed fuel filter, verified leak down rate of the fuel pressure,pulled fuel pump and cleaned strainer, replaced gas cap, checked spark, checked ohms to each fuel injector, cleaned throttle body and checked settings along with a few other things. After a couple of weeks of troubleshooting and narrowing down the problem, took it to a local dealer with an excellent Vette mechanic and he confirmed it was the computer control module. I'm not suggesting your problem is the same as mine, but the point is to set out on a logical troubleshooting journey and eliminate as many possible causes as possible until you hit on the actual culprit or get down to one or two possible causes as I did - at that point I had to get confirmation from the dealer as it was expensive to correct either potential culprit. Replacing CCM's can be very expesive and I didn't want to swap it out if I didn't have to. Some of the troubleshooting is easy - some requires basic mechanical skills along with some tools such as a fuel pressure gauge and Ohm meter. If you can post some other information on the problem - no matter how insignificant it may seem - it may help others zero in on a good starting place. Some of things I completed didn't actually solve the problem, but ended up being good P.M. which may prevent future problems. I'm sure you'll end up getting all the help/expertise you need on this forum.
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
TPS

I had the exact same problem on my 93. The mechanic said it was the ECM and we replaced it only to still have a no start condition. Out of frustration we did what you did and sprayed starting fluid into the TB. Like yours mine started right up. What we finally found was that the TPS was bad. It was telling the ECM that the engine was flooded so the ECM shut down the injectors so the engine could be cranked over to clear the perceived flooded condition. By spraying fuel in to the TB the engine fired and the ECM took that to mean that the flooded condition was cleared and sent fuel to the injectors. In my case the engine idled at 2K. I had replaced the TPS earlier with one from a parts store for 19.95. The new one was a GM OEM part for about 90.00 but the car sure runs great now.

I am including the diagnostic for the TPS from my service manual

Throttle Position Sensor (TPS)
Copied from 1993 Service Manual
The Throttle Position sensor (TPS) is a potentiometer connected to the throttle shaft on the throttle body. It is a potentiometer with one end connected to 5 volts from the ECM and the other to ECM ground. A third wire is connected to the ECM to measure the voltage from the TP sensor. As the throttle valve angle is changed (accelerator pedal moved), the voltage output of the TP sensor also changes. At a closed throttle position, the voltage output of the TP sensor is low (approximately .5 volt). As the throttle valve opens, the output voltage should be approximately 5 volts.

By monitoring the output voltage from the TP sensor, the ECM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor can cause intermittent burst of fuel from the injectors and cause an unstable idle, because the ECM detects the throttle is moving.

If the TP sensor circuit is open, the ECM will set a DTC 22. If the TP sensor circuit is shorted a DTC 21 will be set. A problem in any of the TP sensor circuits will set either a DTC 21 or 22. Once a DTC is set, the ECM will use a default value for TP sensor, and some vehicle performance will return.

A personal note, when my TPS failed it DID NOT set a code other than to tell me the ECM was bad.


 

RonnieH

Well-known member
Joined
Sep 3, 2002
Messages
85
Location
Henrico, NC
Corvette
2012 Crystal Red Metallic
In my previous response, I mentioned I had it narrowed down to two possible scenarios - the TPS was the other. I was leaning toward that solution - I too sprayed starter fluid/ether into the throttle body and the sucker would start up every time - that was my plan b. When I checked the TPS, it indicated it was off a bit, but it didn't turn out to be my problem. If you get down to those last two possibilities as I did, it's a coin toss and you hope you make the right decision on what to replace. Just as a note, replacing my CCM was $400 +. Different jobbers offer rebuilt ones, but be careful if you have to buy one - there have been many problems with low-price rebuilt units.. Right after I put mine in, Zip Products (reputable Vette jobber here in VA) offered one for $90. Best of luck.
 

68Roadster

Well-known member
Joined
Dec 16, 2002
Messages
1,040
Location
Dallas, TX
Corvette
'68 White Vert '05 Silverado SS
OK Jake.....just one catch...you have to let us know what fixes the car.....you see, the one that guessed right wins a prize......
Not really but we all like to learn so it would be great if you let us know what the outcome is.
 
Joined
Nov 9, 2003
Messages
19
Location
North Dakota
Corvette
1990 Black Coupe, 1977 Black Coupe
Sorry this took so long but I've been working out of state and haven't had any time to
work on my '90. This weekend I put a fuel pressure gauge on the Schrader valve on the
fuel rail and it registered 2 or 3 pounds of pressure and would not hold when I shut the
fuel pump off. I checked the fuel filter and replaced it. Then I put the fuel pressure gauge right at the outlet of the fuel tank and still no pressure. Sure looked like a bad
fuel pump. I took the fuel pump out expecting to replace it. I found that the rubber hose between the fuel pump and steel fuel line had developed a hole and fuel from the pump was going right back into the tank. I replaced this short rubber hose and it started right up. It did run rough so I bled the air out of the fuel line at the fuel rail and it seemed to run much better. I'm not sure I'm done yet because I don't know why the rubber hose sprung a leak. My next step is to check the fuel pressure at the rail with the car running. Maybe the pressure regulator is not working and there's too much pressure in the fuel line.
 

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