91 2.8 TBI,Wont Start

[yankees717]

Hi all,
Im having a tough time figuring this one out.A buddy's 91 S10 with the 2.8 TBI,
the injectors will not fire any gas.We did a spark,fuel pressure and pump tests and everything passes GOOD.We tested the pressure and double checked it all.Its getting plenty of gas to the TBI.

Engine cranks over just fine and the car will only fire up if we pour some gas down the Tbi.Then it stalls when the gas is gone,just a few seconds.

The injector harness clips is getting power but the injectors wont spray any gas.

A few days back when problem first started,we poured gas down the tbi and the engine fired up and THEN the injectors started working again and the engine kept running.Then,a week later,the injectors wont fire anymore.

You have any ideas whats causing this problem?Is there a relay that is supposed to signal the injectors to fire gas?Btw,all fuses checked out good.

Thanks for any links or ideas.

[yankees717]

Im posting an update...I found some info online that points to a faulty ignition module not allowing the ecm to cycle the injectors or something...so my buddy is going to give that a try.Will report back tomorrow.

[yankees717]

The old module was bad(it failed the bench test)but a new replacement did not fix the problem.If Anyone has ideas,anything at all,would appreciate it.

Im also going to check the ignition switch on the column.He told me the gauges quit working when this problem happened.Maybe a short somewhere...

[geoffinbc]

Your ignition module sounds like it was not sending a tach signal to the ECM which caused the injectors to remain closed. But since you replaced the module it should be getting the right signal. Do you still have spark but just no fuel?

If you do have a gauge failure then check our your grounds especially the ones on the backs of the cylinder heads They are critical to ECM operation. Also check that the batter to engine block ground is good as well.

[yankees717]

Your ignition module sounds like it was not sending a tach signal to the ECM which caused the injectors to remain closed. But since you replaced the module it should be getting the right signal. Do you still have spark but just no fuel?

If you do have a gauge failure then check our your grounds especially the ones on the backs of the cylinder heads They are critical to ECM operation. Also check that the batter to engine block ground is good as well.

I was mistaken about the gauges...I checked them and they were working...my buddy thought it quit.

Yes we still have plenty of spark,just no inj spray.FP is good too.

Thanks...we have tried 3 new ign modules and theyre all bad...we took them back to the store and they tested them and they all failed.I guess thats what happens when you get Duracrap junk.

Ordered another module from napa,will be here tomorrow,hopefully will fix the problem.Did not find any ground problems either.Will keep ya posted.Thanks for the ideas.

[geoffinbc]

Go to a GM dealer and buy an AC Delco module. I once had a rebuilt distributor with a band module in it.

[yankees717]

Go to a GM dealer and buy an AC Delco module. I once had a rebuilt distributor with a band module in it.

I agree...isnt my money though.I always used the a/c delco stuff,but friend needed to get it done cheap,and so far has been a disaster.If this doesnt work,Im gonna tell him to get the a/c delco piece.The dealers around here mark things up too much,its almost cheaper to mail order it from ebay or partsdirect instead.

[geoffinbc]

Well if you know anyone who works in the parts or repair industry get them to call the dealer and they should be able to get the part at cast plus 30%. I never run into a problem at dealers because I get everything at cost plus 10%

And you don't have to get Delco parts at a dealership local parts stores carry them too and so does rockauto.com

Or the other trick I use is print the price off the internet and then take that into the store and say if you have it I will buy it now but I can get it at this price on the internet how close can you get to this?

[yankees717]

A new delco module didnt fix the problem...also took the old module to another parts store and it passed on the machine this time LOL....the autozone machine was failing everyone of them.

Anyways,another tech friend says the problem is most likely the pick up in the distributor,since everything else checks out.
That sound right?

[geoffinbc]

But if the pickup was gone you would not have spark. And you say it runs when dumping fuel down the intake. Go and pick up an injector noid light. It will plug into the injector plugs and flash if there is a working signal when the engine is cranked. And another question. Do you have fuel pressure with the key on and in crank mode?

I would try another quick check. Give 12V power to the fuel pump prime lead. It is located below the 12V power post on the firewall and is a gray wire with a single black connector. Give it 12V from the post above and it will force the pump to run constant. Now try and start the truck.

[neo71665]

But if the pickup was gone you would not have spark. And you say it runs when dumping fuel down the intake. Go and pick up an injector noid light. It will plug into the injector plugs and flash if there is a working signal when the engine is cranked. And another question. Do you have fuel pressure with the key on and in crank mode?

I would try another quick check. Give 12V power to the fuel pump prime lead. It is located below the 12V power post on the firewall and is a gray wire with a single black connector. Give it 12V from the post above and it will force the pump to run constant. Now try and start the truck.

For the most part I agree but when my dizzy went out earlier this year it gave me hell. I swapped out all kinds of parts and couldn't pin point it until I finally let my dad talk me into trying a different dizzy. Turns out it was firing but no where close to where is should be and wouldn't crank the engine. My dad has been a mechanic for 20 something years and my uncle even longer and neither had ever seen anything like it.