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 ain't 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.
It is very important to work through the problem with some logic rather than changing parts on a hit or miss basis.
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.
If the car does not start:
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.
3. Is the Check Engine light illuminated when the key is turned to ON? Check the ECM-IGN fuse, the ECM-SOL fuse, and might as well check the CCCI fuse while you are down there. The No Check Engine light troubletree 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. 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.
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:
no spark, but have injector pulse - Check the Ignition Module (also check the CCCI and ECM-IGN fuses)
have spark, but don't have injector pulse - Check the Cam Sensor or ECM
have no spark or injector pulse - Check the Crank sensor or the Ignition Module (and fuses)
This above is a very good way to cut to the chase and start zeroing in on the problem(s).
Armed with the answers you obtained in the above five steps, go to the "No Start" trees and find your starting point. Do the tests suggested.
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.
If you want to maximize the odds of keeping the engine together as well as successfully work on your car following the information provided, you will need the following equipment at a minimum.
Now, for some Rant Time! I often get emails from people asking for help. When I ask them for scan tool data, they say they cannot afford to buy one. Yet these same people will list $100's of dollars of parts they have bought hoping their problems will be fixed. A scan tool will do a couple of things. First, it will show you the various parameters and trouble codes from the ecm so you will know if your car is running properly, or if there is a problem. It is not 100% comprehensive, but, it will provide clues and direction in most cases. Secondly, it will provide a full time monitor for timing retard which is the indicator for detonation. People are always telling me that they don't have detonation. I ask them how do they know and they reply that they don't hear any. Consider this. We are running a turbo engine and that turbo forces at least twice the air into the cylinder at stock levels of around 14 psi as compared to a non aspirated engine. This means combustion pressure is much higher than in a normal engine and detonation ramps up so much quicker that by the time we hear it, something is fixing to break. That is at the stock level. Many of us are running much higher boost levels and the problem tends to go up exponentially. You don't get a second chance very often above 20 psi. Watch for timing retard and don't let anyone tell you it is normal! Get a ScanMaster and watch it like a hawk. One day the car is perfect and the next day a boost hose on the waste gate may crack or pop off and the engine can be toast in seconds. The big advantage that the Powerlogger gives you is that the data may be recorded and all parameters studied after the fact in detail. It is also nice to be able to post a log so others can help you without asking a jillion questions and you don't have to make numerous runs to watch all the parameters. In conjunction, the Powerlogger will feed the ScanMaster and extend the parameters that may be seen at a higher data rate. Put one on your Christmas list!
It is a tough call if you can only afford one, or the other, initially. Each costs around $250 unless you get lucky and find someone selling an used unit for less. I like the Scanmaster because it is always on and always showing timing retard which reflects the potential presence of detonation. Between timing retard and the default display of O2's, you can often avoid major problems. If you understand basic tuning and have some car experience, this would be my first choice. If you are completely new, the Powerlogger will enable you to post data logs online, or send them to someone, in order to get more comprehensive trouble shooting or tuning help which should get you up to speed faster. The downside is that you don't have that constant warning of timing retard in your face. If you have enough sense to take it easy and get everything working properly before you start hammering the car, this may be okay. As I stated above, if you are going to turn the boost above 16 psi whether running race gas or spraying alcohol, then I strongly suggest Powerlogger. An audio knock alarm, altho not 100% accurate, might be a wise investment for protection if you don't have a Scanmaster as well as Powerlogger. I have all three (PL, SM, Knock Alarm)
I can figure problems out much faster if I can look at a log from PowerLogger. I can spend days try to extract info to help someone that a single log would instantly provide.
Beyond that, it sure helps to have a factory shop manual from Helms. As far as I know, the Helms are discontinued but you can sometimes find an used one. (if you cannot find a paper copy from Helms, get the CD version from Jeremy Woods. He has started giving it away. 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 )
A coil /module tester from Caspers can help you sort out module and coil problems (it works only on the factory modules and not aftermarket versions that are built differently). Another useful tool is Casper's Cam sensor tool although your volt meter will serve the same function. Having two cars to swap parts between is an easy way out, but, it may not solve the problem given the age of the wiring we are dealing with. As far as I know, the Helms are discontinued but you can sometimes find an used one.
I don't know
how anyone owns one of these cars without a shop manual. The
electrical section, alone, is worth the price of the CD.
One thing that has saved me many a time is a digital camera. If you are going to redo the brakes, or rebuild an alternator, before you dismantle everything, take a couple of pictures of the assembly. I have a tendency to look at things and say to myself, "I can remember that". A month later when I decide to put it back together, I don't have a clue. A picture is really nice to fall back upon.