I read every post and still nothing!

[JaredsDad]

87 Blazer 350tbi wouldnt start. Tracked it down to no spark. Repplaced the coil and I have spark. When I try to start it, it fires right away but dies instantly. I checked firing order, I can hear the fuel pump come on, replaced the fuel filter and fuel pump not very long ago. I also checked the injectors with a noid light and they are fine. I went over every inch and checked to make sure I didnt disturb anything. My last thought is ign. module but if Im getting spark could that still be the problem? Please help. I cant find a post with a prob like this. Sorry for the long winded post. Its been a while, the site looks great!

 

[bowtiepower00]

The Distributors go bad too, usually the hall effect ring or sometimes module. Or, the bushings can wear out and cause wobble and problems too. For all things TBI related, check out: http://www.thirdgen.org/techboard/tbi/ It is the best source of TBI knowledge I've found.

 

[Blue85]

Does it start every time and die every time? You could be running on only the prime pulse due to a bad relay or oil pressure switch. Can you hear the fuel pump stop?

 

[JaredsDad]

Yes it starts and stops every time. I can hear the fuel pump stop. Can you give me a heads uup as to where the relay and oil pressure switch are located? I'm in colorado and my manual is in wyoming. I should just go buy another one. Thanx

 

[JaredsDad]

Does it start every time and die every time? You could be running on only the prime pulse due to a bad relay or oil pressure switch. Can you hear the fuel pump stop?

So I just read a deal on third gen that leads me to believe that there is no way a bad oil pressure switch would cause a fuel pump to not have power. That in fact, it includes a redundant 12v line in case the relay gos bad but has no shut off capabilities. Who's right? and if that is the case since my relay seems to work fine when tested, could a bad ign module be the problem even though it gets enough spark to start for that oh so brief moment. I fought this for 7 hours yesterday and 3 today. My patients are running out. All help is very very appreciated,

 

[readymix]

Are the injectors firing fuel when you turn it over??

 

[JaredsDad]

Yes the injectors are firing when it turns over. It will start and run for about 2 seconds every time. But after 2 sec it dies. I just replaced the ignition module if for no other reason then to eliminate it. I left the ignition on and killed the battery so now I must wait to see if that was the end all solution. Just one of those days!

 

[dyeager535]

You are right on the oil pressure switch. If your relay works, then you don't need it.

 

[JaredsDad]

Well, it turns out it was the ignition mod. after all. I still dont understand why it would spark to start and then not, but its fixed. Thanks for all your help. I've been away for some time now and its great to be back! I love this place!

 

[Blue85]

OK, I'm still curious. Does the ECU turn off the pump if it detects a bad module? I was sure the problem was the fuel pump relay.

 

[ryoken]

I've found more often than not, the relay is not an intermittent prob.. When they f*ck up, they chit the bed... And iirc, yes, the ECU detects an ignition issue and shuts down the relay.. I'm in the process of eliminating this in my system...

He could have eliminated the relay as a possible issue by running it off the 12v bypass pigtail (red wire) out of the relay..

Jaredsdad - ignition modules are notorious for having probs only when hot... cracks expanding, etc.. Tho in your case, it sounds as if the motion/signal thru the part was causing the failure...

I keep a known good, spare in my console...

 

[JaredsDad]

I've found more often than not, the relay is not an intermittent prob.. When they f*ck up, they chit the bed... And iirc, yes, the ECU detects an ignition issue and shuts down the relay.. I'm in the process of eliminating this in my system...

He could have eliminated the relay as a possible issue by running it off the 12v bypass pigtail (red wire) out of the relay..

Jaredsdad - ignition modules are notorious for having probs only when hot... cracks expanding, etc.. Tho in your case, it sounds as if the motion/signal thru the part was causing the failure...

I keep a known good, spare in my console...

I eliminated the relay excactly as you described, I was sure that was the problem.

I never had a problem while at or near operating temp. That to threw me for a loop. When I wasnt geting spark, I changed the coil and it fixed the spark prob so I disincluded the ign mod as a suspect. Oops

 

[Thunder]

OK, I'm still curious. Does the ECU turn off the pump if it detects a bad module? I was sure the problem was the fuel pump relay.

If the ECM does not see a spark siginal (Bad module or Pick up coil ect) it will not fire the injectors. I believe the fuel pump realy still remains energized.
In a no spark condition the ECM turns off the injectors so the engine will not flood.