Why wont my truck start

[shaun]

So I drive around all day just like any other day, go to a friends house, then we get ready to leave my truck wont start. Everything had been fine before no symptoms, nothing funny. So we started "troubleshooting" and first thing I realized was my injectors werent spraying when we cranked the truck. So I listen for my fuel pump. Sounded like it was coming on when you turned on the truck but to be sure I checked the fuses. No blown fuses. Well next I replaced the fuel filter (since I had one and this has been a problem before). Then just to make sure fuel was getting to the TB I pulled the fuel lines and had my body crank it, sure enough the TB is getting fuel. So then I figured a sensor. So we check the TPS. It was good. Then the MAP sensor it was good. So I decided to pull the TB I mean what else could it be. When I pulled the TB I noticed that the IAC was broke, It was just barely hanging on. When I w2as having all my idling problems before I had a shop look at it and they replaced my IAC. Well apparently it was overtightened because the valve itself was basicly sheared off the threads. So now I have to easy out those threads so I can replace the IAC.
Would this cause my injectors not to fire or am I still going to have my problem after replacing the IAC?
If so what else could it be?

Info
1990 GMC Jimy
350 TBI 200,000 miles
All sensors are new and TB has less then 5000 miles on rebuild (and yes there is a full tank of gas)

 

[shaun]

anybody?? Would the IAC cause this???

 

[Ryan B.]

How do you know the injectors aren't spraying? I'm not familiar with TBI but do you hook a test light and check for the light to pulse like you would with TPI. For my tpi, there is a fuse for both the drivers side injectors and the passanger side injectors.. You said you checked fuses.. did you check to see if your getting voltage out to the injectors? You said you hear the fuel pump but are you getting enough fuel pressure? check it with a gauge? I'm really not familiar with TBI at all.

Your tracking down the fuel side here since you said the injectors aren't spraying?... but did you check for spark!? Pull out a spark plug and hold it against something metal while you get someone to crank it.. make sure your getting spark at the plugs... then you know it has to be fuel related since you have spark and air. /forums/images/graemlins/thinking.gif

 

[shaun]

You can see inside where the injectors spray. I have checked all fuses and I dont know how to check if there is voltage to them or what ie should be? The book says get a special injector tester?? I have checked for spark just to rule it out and I had it so I know that isnt it. Pressure wise: 9 - 13 lbs isnt very much but if I hold thr fuel line coming into the tb while my friend cranks it and then let go after he stops it will shoot fuel across the garage so I am guessing there is probably enough pressure. Does the IAC have any control over the solenoid in the injectors. Could a broken (as in cracked from the tb) cause this?? Thanks for your input ryanb. /forums/images/graemlins/waytogo.gif

 

[k20]

well i always say this lol, but i had a prob, no start, very little or no fuel being sprayed. If you have a NOID like make sure the injectors are getting an impulse to fire, it should light it up really good ( a NOID light you hook into the harness that plugs in the top of the injector). If it is getting an impulse( even if its weak) I would say check the temp sensor that is in the manifold (not the head) and replace it. Mine stuck so the truck was hot, so when the block and truck were at 50 deg the comp thought it was 210, and when its hot it gets less fuel hence no start. If its not getting an impulse to fire that could be the ECM.

 

[jfortner]

Check your fuel pump pressure, especially if it barly runs or only runs if you floor it / pump the gas alot. Mine had low pressure and caused it to barly run until it got warmed up even though the fuel pump sounded / pumped fuel normally.

John

 

[MTBLAZER89]

It turned out to be the spark module. I'm sure he will fill in all the details tomorrow. /forums/images/graemlins/waytogo.gif

 

[shaun]

Well after hours of troubleshooting my fuel system, replacing the IAC (somehow it was broke off my tbi WTF /forums/images/graemlins/dunno.gif)didnt fix it. Checked TPS. It was good (are these only adjustable if you drill out the plastic b/c the holes in the TPS are just big enough for the bolts). Then we checked the MAP sensor. It was good. Fuel filter was replaced annd we checked the pressure on the pump. All was good. So I finally called my uncle (33 year mechanic). He said the symptoms point to a failed electronic spark controller. So I changed and BAM. She fired up. She is runnung rough (I think it just needs to be timed). It sputters and pops but it runs. Thanks to all who helped.

Shaun /forums/images/graemlins/woot.gif