Home Trouble Shooting
Start Troubleshooting Here No Start Trouble Codes Car Runs, but Seems to have a Problem ECM Wiring Coil-Module Wiring Fuses Fuel Pressure Test Fan Circuitry Fuel Pump/Fuel Injector Circuitry Torque Converter Lockup
Trouble shooting used to be a relatively simple business. If the car had spark at the plugs and gas in the carburetor, it would usually try to run. If one was missing, it was generally not that difficult to figure out what the problem was.
It's not that easy most of the time with the fuel injected cars as too many things are interrelated and a flaw anywhere in the system will usually bring things to a halt. To further complicate matters, the wiring harnesses on our cars are 20 years old and connectors may be flaky, corroded, broken, etc. On the other hand, the cars still need fuel and spark to run so if you understand older pre-electronic cars, then it is not that hard to pick these up.
If you are going to maintain your car yourself, you must have some items to help you diagnose the problems. Even if you are going to seek help online, you still need these to be able to provide enough information for someone to help you and avoid swapping parts indiscriminately.
At a minimum, you will need the following:
Quality fuel pressure gauge on a hose long enough to reach the windshield and be read while driving
Noid light that is labeled G.M. PFI or G.M. PFI-B
Analog Boost gauge that reads vacuum as well. A good scale is 30-0-30
A digital volt-ohm meter
There are other items that can be useful as well. Caspers Cam Tool, Caspers Coil Tester, compression gauge, spark tester (I just use a sparkplug and lay it on the valve cover and a copy of the factory shop manual. It's hard to find a paper copy and usually very expensive, but, you can download one free from Jeremy Wood, I believe.
All you have to do is download it here https://kat.ph/trsrvman-iso-t with a bit torrent client like utorrent or from Google Drive here https://docs.google.com/file/d/0B_taSEdSERBnSzlWSkZtT7395056.htmlWJhbjA/edit (if you get a message saying unable to scan because the file is too large, click download anyway)
Now let's try to establish a logical procedure of troubleshooting to try to narrow down a "No Start" problem because jumping around swapping parts is not only expensive, but it can be very frustrating.
Long ago, Jim Testa posted a "How To" get started in the trouble shooting. It is well worth reading in order to apply some logic to the process.
Below is a short cut derived from Jim's article. The below simply applies logic to the No Start troubleshooting trees and can save you a lot of time.
Assuming the battery is charged, the car has compression, and the fuel pressure is adequate, If you have:
1. no spark, but have injector pulse - Check the Ignition Module (also check the CCCI and ECM-IGN fuses)
2. have spark, but don't have injector pulse - Check the Cam Sensor or ECM
3. have no spark or injector pulse - Check the Crank sensor or the Ignition Module (and fuses)
If the car does not start, establish the information required to pin the problem area down to one of the three guidelines listed above.
1. Connect your volt meter to the battery and try to start the engine. Read the voltage on the meter. It should be above 10.0 volts or the car will not start as the ECM will not get enough voltage to operate. It is important to to crank the engine with the starter to put a load on the battery as a battery with a bad cell may read good when there is no load on it, but it can easily drop three volts when the starter is engaged.
2. Check the fuel pressure. It should be up around 40 psi. If it is down in the 20's, it may not be enough to start the engine and you will need to find out why the pressure is low.
3. Is the Check Engine light illuminated when the key is turned to ON? Check the ECM-IGN fuse, the ECM-SOL fuse, and the CCCI fuse. The No Check Engine light trouble tree does not mention the ECM-SOL fuse but I blew one and lost the check engine light and the car shut off. I don't see why when looking at the diagrams but it cost me an expensive wrecker ride to figure this one out. Here is the chart for No Check Engine light. It is a simple process; use it!
4. Does the ignition have spark? Pull a plug out, put the appropriate wire back on it and lay the plug on the valve cover or hold it to a good ground. Crank the engine over with the starter. Do you see a good blue spark across the gap? To avoid any fluke of nature, pull each plug wire off and check it for spark on one side of the engine (this will verify that all three coil packs and the module are working).
5. Pull the fuel injector harness off an injector (mash in on the spring clip on the bottom of the connector and lift the connector off the injector). Plug your Noid light into the connector. Crank the engine. Does the light blink steadily while cranking? (this verifies that the injectors are receiving injector pulses from the ECM and the crank and cam sensors are working) If you don't have a Noid Light, go buy one! A single noid light costs between $7.00 and $13.00 depending on where you buy it. They make different noid lights for different injectors. Be sure you buy the one that is labeled G.M. PFI or G.M. PFI-B. If the Noid light does not blink while cranking the engine, then you do not have injector pulse! Don't try to use a volt meter because you don't see the need for the noid light. The injector will only be getting power for less than 0.002 second. Neither your meter nor your eye is faster enough.
Now, using the information gathered above, you should have a good idea which of the three guidelines above applies and pin the problem area down. Problems with the crank sensor is often obvious if the bracket that mounts the sensor has broken. If not, then check the sensor for proper clearance to all three blades on the back of the damper.
The cam sensor is easy to check if you have a Caspers Cam sensor. Just plug it in and rotate the engine to see if the light on the tool goes on and off. If you don't have it, the trouble tree will tell you how to check for the rise and fall of voltage as you rotate the engine.
The ignition module is hard to check and it is usually easier to swap out than rely on a parts store tester that probably does not work on our modules anyway. None of the aftermarket modules that are offered in parts stores other than the Standard brand module will reliably work in our cars. I cannot say the Standard module will work every time but it has worked for some. None of them will work with the Caspers Coil Tester which only works with the original module. ACDelco #19260720 Ignition Module is offered as a replacement. I don't have any experience with this unit but it apparently works (not with the tester). I would not be surprised to find it was made by Standard but I am guessing.
The best replacement is the TR 6 sold by Bailey Engineering. It costs twice as much but it works as well, if not better, than the original and offers several additional features.
No real way to test the ECM other than to swap it out. It's a good idea to buy one off Ebay or elsewhere to have as a spare.
If the car runs, but does flaky things.....it is always a good idea to check the various grounds...particularly the ground wires that attach to the rear of the passenger head...yeah, the ones that are a pain to get to. Sometimes they are loose; sometimes a wire is broken, and sometimes, there is corrosion in the connectors. It makes life a lot more easy if they are relocated to a stud on the intake manifold, or using a ground relocation kit from Caspers, moved to the firewall. These cars must have good grounds to run properly.
Examine the data logs from PowerLogger and look for things that are not right (of course, look for trouble codes-these will be listed on PowerLogger) Look for abnormal readings like low battery voltage, high blms, screwy maf numbers, flaky tps voltages, and so on.
Don't be afraid to post your data logs online along with a description of what is going on with the car. There are plenty of people willing to help.
In attempt to provide information to a broad audience, I have included trouble shooting trees from the factory manual to resolve no start conditions as well as diagnostic tips for the various trouble codes and other generally helpful information.