'90 Blazer driving me crazy! Will not start.

I'm new to this board and glad to see it. Lots of good information already, and great ideas. I'm hoping someone here can help me. I have checked the posts and don't see exactly the same problem.

My '90 full size Blazer (350 ci w/ TBI, all stock) quit while in parking lot, while idling. All stock. Full of fuel and I have checked all fuses. Turns over great. Have spark at coil and at plugs. Engine will start if I spray carb cleaner or gas down the throttle body. Fuel pump runs at key on. Bypass (jumper across) the fuel pump relay and getting fuel out of return line at throttle body (good flow w/ disconnected line). It won't start with fuel pump relay bypassed. I haven't checked the actual fuel pressure yet. I have voltage at the injectors. I disconnected the TPS to check startup at idle w/o success. I disconnected the timing wire (used to check timing at idle) w/o success. No trouble codes came up. Tried clearing computer by disconnecting battery for about 10 minutes w/o any difference.

I am leaning toward computer but I hate to just throw parts at it (to cheap and an old time mechanic, I like to fix what's wrong).

Any ideas on what I haven't tried? Thanx for any and all help.

Check for a bad ground going to the injector pulse circuit and wiggle the connector going to the computer under the dash to make sure it is in tight.

Some good trouble shooting you have done. Open up the air cleaner and see if the injectors are spraying.

That will tell us a lot.

Thanx for the reply.

I have checked all the grounds I can find. Don't know for sure if I have tried the one you mention. I have made sure the connectors to the computer are tight when I took it out to see how it hooked up. And no, the injectors are not spraying at all.

Trace the injector's ground wire which I think hooks directly to the computer seeing the computer fires the injectors.

Check for a broken or worn wire.

Well, I now know what does not work (I think).

The fuel pressure at TBI outlet is 11 lbs.

The injector's ground wires are good to the computer connector, checked with ohm meter. Also, I have voltage at the ground wires at the computer with the ingition in start mode (poor man's node checker?).

Next I plan to check the injectors to see if by any chance they both clogged up at the same time (yea, right). Beginning to look more like a computer to me. Any other ideas?

Thanx.

Check if the injector's are getting the voltage pulse before you tear anything apart.

your check the voltage at the computer, now check it at the injector.

Maybe I'm somewhat confused what your saying? There is voltage at the injectors first, goes thru the injector and ends up at the computer.

First post, I stated I found voltage at injectors; now I have followed it thru to the computer. Injectors still will not flow. Other than using actual noid tester, what else is there?

I'm sorry, Imust've missed that.

So you have voltage pulse at the injectors right?

all you need to do is buy or borrow the GM TBI 'noid lite from autozone.

injector flash = ecm not totally gone

at the same time, the ign is somewhat independant of the ECM. only the est circuit is controlled, with total ECM failure the ign will still pulse but that does not mean the ecm is listening.

while cranking, use a timing light to check base timing (it will be slow, but it will work) rule out timing problems.

report back.

I just love/hate Autozone. Sometimes they are just great. The noid light from them was just $7. Should have got it a week ago.

No light with noid installed. Still have power to injector/noid light and thru to computer, just not being operated.

Base timing good.

Time to start looking for a computer?

BTY, Autozone lists two computers for this vehicle (#01227747 & 01228747), listed at $75 and $70. Any idea what the difference is?

Thanx.

Can you answer my questions, do you have an injector voltage pulse!

Is there voltage going to the injector?

I thought that's what I said. There is still power (voltage) to injector/noid light and thru to computer. While turning over the engine, the noid light does not light up.

Are you asking about something else?

I thought that's what I said. There is still power (voltage) to injector/noid light and thru to computer. While turning over the engine, the noid light does not light up.

Are you asking about something else?

Nope, that is it.

Sounds like something is wrong with the ignition switch or something.

Have you checked all fuses?

Ignition coil. Controls injector pulse.

A faulty coil will cause no pulse.

How does the coil control for the sparkplugs affect the injectors or how are they related.

I think it's the ground that signals the Injector pulse. Seriously, I've seen countless no-starts that have no injector-pulse solved by a coil. Now, I'll re-read the thread. Do we have spark here? Can't remember.

Yes, we have spark, both at the coil and at the plugs. It will start with fuel poured/sprayed down the throttle body.

BTY, the fuses were checked early on and were all good. I have rechecked them and still good.

hold on a second, have we even checked fuel pressure yet?

I have run across the following problem twice, in a '90 and a '91. In the 90, the fuse would blow and kill the engine, I believe it was marked something like panel lights or something not even remotely related to injectors. After two other mechanics in the shop threw their hands in the air and they had no more hair to pullout, I took a crack. It turned out that where the wire went through the throttlebody, the insulation cracked as well as the rubber and this was shorting it out. On the second unit I found a broken wire in the same spot. I am not saying this is your problem but it is something to look at and check out. Good Luck!

Well, I now know what does not work (I think).

The fuel pressure at TBI outlet is 11 lbs.

The injector's ground wires are good to the computer connector, checked with ohm meter. Also, I have voltage at the ground wires at the computer with the ingition in start mode (poor man's node checker?).

Next I plan to check the injectors to see if by any chance they both clogged up at the same time (yea, right). Beginning to look more like a computer to me. Any other ideas?

Thanx.

Yes, the fuel pressure has been checked. The wiring looks and checks good. No fuses are blowing. Haven't had a chance to tear into the injectors yets.
I have found a local impound yard that will allow me to borrow a known good computer for checking before I go buy one. Will let you know what I find.

Check out this site
www.chevythunder.com/gm_throttle_bocy_injection_pg_1.htm

It has some more good info and troubleshooting about GM TBI.

Sorry, I'm not adding the underline. And it's messing up the address. Try chevythunder.com/gm and follow the links to TBI.

GOOD NEWS! IT'S FIXED!

The boneyard computer did it. And now it runs like it should.

Thanx for all the advice and information.

BTY, chevythunder.com is also a good site for information.

That is awesome! Works great now?

how much is the comp going to cost you?

BTY, Autozone lists two computers for this vehicle (#01227747 & 01228747), listed at $75 and $70. Any idea what the difference is?

Thanx.


It took the 1227747 unit @ $75. plus tax.

Turns out this unit fits different trucks w/ engines from 4.3L to 7.4L. There is a different chip installed to match the engine and performance levels.

Why didn't you just use a used one?

The computer I used came from a local impound yard and was borrowed. And I like warrantee's.

sure, just checking and good luck.

I didn't know companies made aftermarket computers for trucks.

BTY, Autozone lists two computers for this vehicle (#01227747 & 01228747), listed at $75 and $70. Any idea what the difference is?

Thanx.

The helpful guy at www.tbichips.com told me the difference is mainly because the 01228747 computer was not used with the 700R4 OD transmission.

BTY, he specializes in GM TBI's from '87 to '95 and has lots of good information about TBI in general, not just about his chips. Check him out.