TBI engine not starting

[67ChevNut]

I have a 69 GMC with an 89 tbi 350 engine. I recently removed the distributor because the truck had a misfire when running. Problems got worst after that, now it tries to start, it will almost start for a second, but never really does. Distributor has been removed and reinstalled twice and timing set every time, rotor pointing to number one, number one wire where rotor was pointing to number one. Timing mark was placed at 0 too.

Truck has fuel, there is fuel coming out of the injectors. I also pour a little fuel when trying to start and it tries to start when I do that, but it actually never does. I took the spark module to get it tested and was found to be in good working condition. I must add that I have replaced almost every sensor, cap and wires less than a year ago. The fuel pump is also new. I have a spark tester and the last time I checked, it did have spark. I also used the spark tester on the coil and the light comes on when the ignition switch is on. I replaced the rotor last week with a new one, I also cleaned the spark plugs because they were black. Truck used to run before this problem. Problems started since we messed with the distributor, so I suspect there may be a problem with the distributor, or distributor components, not so sure. Maybe the timing is wrong, or maybe the wires on the cap are not exactly staring on the correct number one spot, but I have checked this two or three times already. I am out of ideas right now and a bit frustrated. What should I be doing next to get it fixed?

[sntrym95]

I'd check the plug wires again. number 1 should be in front, slightly to the drivers side. firing order is clockwise, so number 8 is towards the passenger side. Firing order should be 18436572. Check the coil to distributor wire as well, maybe it's loose. Add some dielectric grease to the dizzy cap points to make sure you're getting a good connection.

[Twin Turbo Skylark]

Okay to start with here is what I would do:

1. remove all 8 of the spark plugs and dry them out. You may have flooded the engine so bad it wet the plugs. Then put the plugs back in or new plugs is a good idea even. But leave number 1 plug out.
2. Drain the oil and put fresh oil in there as it may well be fuel contaminated and that could damage your engine.
3. put a wine cork in number 1 spark plug one
4. crank the engine over by hand (wrench on the harmonic balancer bolt) till the wine cork pops out. This makes sure you know you are on the compression stroke of number one. You may be on the exhaust stroke.
5. now look at the timing tab and line 0 up with the slot on the harmonic balancer.

Next take the cap off the distributor and have a look to see if the number one spark plug is directly above where the rotor is pointing. If not then you need to remove the dist. and stab it in so that the rotor is directly under the number one plug wire terminal.

If you do all that and it looks good then put the number one plug on the wire but not into the head, lay it on the intake manifold and have a freind turn the ignition key to see if you are getting spark at the spark plug... Just watch the gap for the spark, and instal it and fire up the truck if the spark looks good.

99% chance the distributor is in wrong.

[67ChevNut]

I have not had a chance to try your guys advice, weather hasn't been so good out here. I may be able to do it today, sure want to get it running asap. Let you know what happened. Thanks for the replies.

[Twin Turbo Skylark]

Originally Posted by 67ChevNut

I have not had a chance to try your guys advice, weather hasn't been so good out here. I may be able to do it today, sure want to get it running asap. Let you know what happened. Thanks for the replies.

I hear ya, -4 Degrees F here today BRR....

[67ChevNut]

Well, truck started today. Tried all suggestions, twin turbo nailed it. I cleaned the plugs, I replaced the distributor cap, checked the timing again, filled the gas tank, moved the distributor a bit to help it start better, and wala! it started! It felt great.

Engine does have some explosions when I accelerate the gas pedal, it runs ok otherwise. I drove the truck like a block or so, it dies when I accelerate all of a sudden. Thinking number one is on the exhaust point, how exactly do I fix that, if I have to? Maybe I just need to fix the idle, thought that if the timing was wrong it wouldn't work at all.

[68c10airstream]

Worked as a gmc dealer mechanic from 89-97. Went to gm specialized electronics training and the number one problem facing tbi motors as they age is a corroded distributor ground. Typically after the distributor has been moved the trouble starts. I've even seen trucks come in for an engine replacement with no codes and leave to only return with trouble code 42 (est bypass fault)

I'll describe it this way; where does the ignition module bolt to?? The distributor body. Do you see any black colored ground wires going to the distributor?? No!

When the dist. gets moved around it rests in a new position and the hold down now rests on a highly corroded area. The test is to take a voltmeter on the "dc" scale, start the truck, let it idle, and now take one voltmeter lead and touch the battery negative terminal, and take the other lead and touch it to the neck of the dist. that you shined up earlier with sandpaper, etc. If the meter reads any value you need to do this;

completely remove the hold down and shine up the underside, take a razor blade or a straight blade screwdriver and scrape the area that the holddown touches at the base of the dist. Completely clean the holddown bolt.

So now the module ground goes directly through the dist body through the hold down and bolt to the intake manifold and to the block. You can also clean the intake where the holddown touches.

Never put a single part in to repair the code 42. The reason for the code 42 is the fact that when you are driving the truck down the road the spark advance circuit adds a little more load for the ignition module, hence the code.

I should add that because of the poor ground when you are doing the voltmeter test the meter reads a value because that is the amount needed to satisfy the ground needs. You are making a parallel ground circuit with the meter.

There are other dist issues that plague this style and gm hasn't made the part in years. It the center spinning piece that the rotor bolts to. The pointed reluctor piece that is pressed onto the shaft loosens up after time, the cast in place magnet in this area gets cracks and gets weak. In the late 90's when i worked for an independent repair shop i probably put in 8-10 new gm shafts in v8/v6. Pick up coils were a failure item but hardly a module.

[67ChevNut]

Good advice 68c10airstream. I will follow your instructions and try to get better ground on the distributor, I wiill also check on that shaft. Hope that makes it better.

[68c10airstream]

For tbi motors here are the tests from memory;

No start, no spark? remove the plugin at the distributor and find the purple with white tracer wire in the plugin. Take a 12 volt test light (old school with a bulb,not led) and hook the alligator lead to the positive terminal and touch the point to the purple wire with the key on. Touch repeatedly on/off the pointer and watch for the coil wire to spark to ground (wire removed from cap and out of the way, maybe on top of the valve cover) and watch for injector pulsed spray at the same time. What's happening is you are sending a toggled 12+ signal into the purple wire (rpm reference) that goes to the ecm. The test light bulb acts as a current limiter (remember that the pointer is 12+ before the circuit is completed).
All of these tests can expose you to coil sparking and can POTENTIALLY KILL you, you have been warned!!

Pickup coil test: if you suspect a bad pickup coil in the distributor, a quick and dirty test is this; Fuel pump fuse removed, take a soldering gun plugged into 120volts and pass it under the dist. body under the module area with the gun trigger on. Remember to pull the coil wire and place it near the valve cover. With the ignition key turned on and the soldering gun on and under the module the radiating magnetic field induces about a 3,000 rpm signal into the module and the coil wire should get very busy sparking like mad. (if you didn't pull the fuel pump fuse the fuel injectors would flood your engine.

Tests with the distributor removed;
pickup coil unplugged from the module, take a volt meter on the ac volts scale and spin the dist. shaft. If the pickup coil is good and the magnet is strong you should see 300 millivolts ac. That's .3 volts, not much. Pickup coil leads should be insulated from ground.

Dist. shaft magnet strength test; with the dist. in your hands and spin the dist. Provided that the shaft spins easily watch and feel how the shaft comes to rest. Does it line up the points with the pickup coil and latch into alignment, may even just go past alignment and spring back into alignment, or does it stop where ever it wants. If it lines up=strong magnet. Look at the magnet and see if it's cracked in many places. If so this breaks up the magnetic field and is weaker.

Dist. test with it installed in the engine; remove the cap and rotor and take a straight blade screwdriver and push the shaft's reluctor points and try to push it clockwise and then counterclockwise. As you change directions and go past the gear/cam gear slop (lash) push it a little harder and see if the pointed reluctor shifts on the shaft?? This pointed reluctor is pressed onto the shaft and it sits on a serrated area of the shaft and looses tension over time and shifts back and forth. I think gm stopped production 15 years ago of the new shafts but have not checked in years.

I found the loose reluctor on a truck that i repeatedly checked timing. With the timing single wire disconnected (base timing check mode) sometimes i would have 0 degrees timing (the spec i think) sometimes -3 degrees, sometimes +4 degrees timing. Remember that if you check timing with the wire connected timing moves all over the place and it's normal. What happens is this; the ecm is shooting for an idle rpm target and the idle air control valve is a stepper motor and is a rough coarse adjustment and to fine tune the rpm's it raises and lowers the timing to get there.

Now on to your hesitation on tip in; disconnect the egr valve and drive it. If the hesitation is gone, take a mirror and look at the 8 digit gm number on the back of the valve and pay attention if the number has a "P" or an "N" after it. "P"= positive pressure, "N"= negative pressure. The "P" labeled valve were the one to give trouble. Provided that you exhaust isn't plugged up the valve has an inner disc (valve) that closes under exhaust pressure and allows the valve to open, another words it modulates the valve opening rate based on exhaust pressure. It this is happening remove the egr, turn upside down and spray carb cleaner into the base area and take a plastic handle of a screwdriver and tap on it repeatedly. You will be able to check to see if it's fixed by taking a vacuum hose hooked up to it and suck and try to open the valve. If the internal disc is stuck the valve will open with suction, if the disc is loose (the way it should be) the suction can't open the valve.

My old brain is starting to hurt now digging all of this up, good luck.