1990 Suburban won't start

[YohDave]

I'm new to the board, so forgive my ignorance in advance. I'm trying to repair what may be a complicated issue by myself.
I have a 1990 GMC Suburban 2500 7.4L 2W Drive. I was driving to work last week and the car completely cut out. I could not get it restarted.
Since then I have replaced the Fuel pump, fuel filter, fuel pump relay, ignition coil, distributor (the entire distributor including pickup coil and module), plugs, plug cables. I still can't get the truck to start and I'm at my wits end. Any suggestions of what to look for next? Sorry for the long post. Thank you.

[jdl]

What kind of testing did you do before you replaced everything? Were there any trouble codes?

Have a helper crank the engine, while you check for spark at the plugs, anything?

With the engine cranking, do you see the injectors spray pattern? How is the fuel pressure?

[YohDave]

I'm in some areas that I have never done work before, so again, forgive my ignorance, but I'm trying.
As far as the Fuel Pump, I simply listened for the fuel pump hum. When I didn't hear it, I figured it was just the pump. The rest of the changes were suggested at the parts store. Unfortunately I don't have a pressure tester and honestly I don't know where to check the pressure.
As for the injectors, I'm not quite sure where to look for a spray pattern, also I'm not sure how to test for spark. Any direction would be great. Thanks.

[jdl]

To test for spark, you pull a plug wire off the plug, You can use a known good plug in the boot. Lay metal part of plug on metal part of engine, have somebody crank engine, watch for spark at tip of plug. You can get a cheap spark tester at the auto-store. I have used a phillips screwdriver in the plug boot, hold shank of screwdriver close to engine ground, crank engine watch for spark jump to ground, probably safer to use a spark tester. You don't have to hold it in your hand.

As far as the injectors, I guess your TBI, you remove the air filter housing, the injectors are in the top of the throttle body, got a couple of wires going to each one. Gas should squirt out the bottom of the injectors, with the engine cranking.

[YohDave]

Thank you for info! I'll give it a shot and let you know the results.

[YohDave]

Hi. I'm working on the car without a helper, so I'm somewhat at a disadvantage. After several attempts at getting it to turn-over, still nothing. I'm getting spark, however, from the best I can tell, I'm not getting spray out of the injectors. I was thinking of getting a noid lite. Would you recommend that approach? If I'm getting current to the injectors, but no fuel spraying, do you know of a next step. If I'm not getting current, any ideas there? Thanks for the help.

[jdl]

When you say it won't turn-over, that means it won't crank? Does it crank, when you hit the starter?

You really need somebody to crank the engine while you do the testing.

The B+ to the injectors should go hot when you turn the key on. You can unplug the connector from one of the injectors, turn the key on, check for voltage at one of the terminals with a 12 volt test-lite. If there is no voltage, you may have a blown fuse, somewhere.

Yes, if you use a noid lite plugged into the injector plug and crank the engine, the noid lite should flash, meaning, there is B+ and ground at the injector plug.

You should have done your testing before you bought any parts. You can't hardly do any testing without a helper to crank the engine. I don't know how you tested for spark at the plugs without a helper? I guess you could lay the spark tester where you could visibly see it, while you cranked the engine. Are you sure you have spark with the engine cranking?

I reread some of your posts, so the pump won't run? My hearing is no good, I can't sit in the vehicle and hear the pump run. Before the vehicle quit, could you turn the key on and hear the pump prime from inside the vehicle? Just by turning the key on, not cranking, the pump should run for a few seconds.

There should be a fuel pump prime connector, You should be able to trace it from the relay. I believe it is a red wire. You can run B+ to that connector, the pump should run. After you hook it up, you can listen at the rear of the vehicle. Don't have to use the key or anything. If you run B+ to that connector, you have to be sure what your doing, I can't see it from here. If you try that test don't forget to unhook the wire.

[YohDave]

Thanks for taking the time to post a response. I have learned my lesson the hard way on this one. Being the only vehicle I have, I was in a rush to try to get it working again and did what I thought was right based on what others were telling me to do.
Yes, I can hear the pump turn on and prime. That I'm certain of. I did place the spark tester where I could see it, but it was getting into the early hours or the morning, so maybe I saw (or thought I saw) what I wanted to see. I'll try it again.
I do know for certain I'm not getting fuel spraying out of the injectors. I had my 2nd grader crank it for me last night while being right on top of the TBI. By the time I got to NAPA last night, they were closed. I'm going to pickup a noid light tonight.
Thanks again!

[YohDave]

Tried getting spark again tonight, and no spark. Also can't get a voltage readout on the injector. Any thoughts on next steps?

[jdl]

I can't tell you how to spend your money, as far as parts and testers. It's your money, your decision. All I can do is give you ideas.

I don't know how you checked for voltage at the injectors? If I was looking for voltage and didn't care about the ground side, I would use a 12 volt test-lite. So you see, here we go again, if you don't have a test-lite? I can't tell you to buy all this stuff.

If you use a test-lite, ground the alligator clip to a metal part of the engine, that you think is a good ground. With the plug loose from the injector, touch the pointed end of the test lite to one terminal or the other, with the key on, you don't have to crank it. The lite should come on.

If the computer doesn't see an rpm signal, it won't ground the injectors.

I can't believe you replaced all those parts and didn't know how to check for spark at the plugs. Even if your just killing time, shooting the breeze. Ha, I'm doing the same thing. Every post I make, gives me more credibility on this site. I don't mind talking to you. thanks

[YohDave]

Thanks again for your ideas. I'm learning a lot about engine electrical and fuel delivery systems quickly. If I could, I would just take it to a shop. However, with 6 kids to take care of, every dime is important. I don't feel too badly about changing out the parts that I replaced. Even a visual inspection showed the parts were either worn out or wearing out quickly. For instance, the sock at the end of the pump was completely disintegrated.
This is my only vehicle and I can't continue renting a car, racking up more costs.

Yes, I did use a 12V test light. No, I did not get it to light. I'm also positive there is no spark. I took the distributor cap off and the rotor does turn. Even if the timing is off, the chain shouldn't be broken (which a guy at NAPA swears it was a broken timing chain). I greatly appreciate your help. Your ideas are the most credible that I have received. Thank you.

[2000CAYukon]

The ignition module on your 90 takes the ac signal from the pickup coil and converts it to a dc signal that the ECM uses to control the fuel injectors and the ignition timing.

I don't have the factory manuals in front of me but you can test if the ignition module is sending the signal to the ECM using a test light. I can't remember which wire it is but it is in the 4 wire connector.

This link shows the ignition module but note that the ECM pins are different on yours http://www.slantsix.org/articles/dib...odule-schm.jpg

Some parts stores can test the ignition module.

If the ignition module is sending the signal but you still dont have spark, it is probably the ignition coil.

//2000CAYukon

[YohDave]

Thank you. I'll check the Ignition Module tonight.

[2000CAYukon]

Originally Posted by YohDave

Thank you. I'll check the Ignition Module tonight.

The reference signal sent from the ignition module to the ECM is a purple/white wire.

Pickup coil resistance should be 500-1500 ohms.

//2000CAYukon

[YohDave]

Thank You. I get spark going to the ignition coil. However, I can't get a voltage reading going to the 4 wire lead going into the ignition module at the back of the distributor. I have checked with a test light and a voltmeter. Any ideas? Thank you.