Help!

[chevykid91]

Hi guys, I have really appreciated all the help from you before. Here's one thats got me stumped. I have a 94 gmc yukon 5 speed. I had a few problems with it previously and like no starting when hot. I have replacedthe coolant temp sensor, distributor( includes pickup, module, cap and rotor) brand new. coil. I started have a no spark problem so I replaced the distributor under warranty. now its an intermittant no start because of no injector pulse. it starts when cold, and when it feels like it when its hot. if it does not start, one of the injectors will give a quick spurt of fuel as soon as you hit the key and also as soon as you release the key from cranking it. I'm going to verifiy spark tomorow, but if it does have spark and fires up with starting fluid what should I look at next? and if I don't have spark and no fuel what are the possibilities. I really love driving it and don't want to give up at this point. I've already put a ton of man hours into this rig and am stumped. If anyone has any suggestions I thank you ahead of time.

 

[SunlitComet]

did you put hermo silicon grease between ICM and base inside the dizzy?

 

[chevykid91]

doesn't the new distributer have that. I'll do it anyways just to be sure. will that cause it to overheat and give a no start?

 

[SunlitComet]

very possible.

 

[chevykid91]

its has grease under the module, maybe if I caked on more? heyif worse comes to worse, I'll convert it to a carb, lol

 

[SunlitComet]

what is the injection pulse issue you have?

 

[chevykid91]

its pretty much non exsistant when its hot. When its hot sometimes the injectors work sometimes they dont. one of the inj. will spurt when you first touch the key and also when you release the key. and sometimes they will work fine. It always happens when the engine is hot, but also occasionaly when its humid and hot outside. basically somethings killing the injectors. I'm really just out of options at this point. would a carb convert be dificult?

 

[SunlitComet]

the injectors are + power fed and negatively switched on/off by the ecm . check to make sure the red and white wires on injectors are getting proper power when ignition switch is on.

 

[chevykid91]

Will do, if they do not have proper voltage. Then i'm assuming its either wiring or ecu.

 

[retorq]

Do you get fuel pressure when it's in the no start stage?? I had my truck vapor lock on me once, wouldn't start until it was cooled down. I have a gauge on mine and was able to verify 0 pressure.

 

[SunlitComet]

Will do, if they do not have proper voltage. Then i'm assuming its either wiring or ecu.

Assuming you are talking positive side of voltage, that would be from bat to fuses to ignition switch to more fuses to the injectors. From the injectors to ecm you would be looking for the negative side of voltage. Ground basically. When the key is on and the ground side of injectors have a decent low resistance ground they will activate open. If there is a break there the ecu may not be able to command them open properly.

 

[chevykid91]

I have .65-.7 volts at each injector. With it running or just ignition on. Truck is not giving me a no start today its cold and rainy out, thats prob why. But i am getting spark. Ill have to t something into lines for fuel pressure its tbi no test port. Im thinking this will be a wiring issue or pcm.

 

[SunlitComet]

Is this measurement taking after the the power goes thru the injectors? Exactly what physical point did you get this reading?

 

[chevykid91]

it was when I turned the key on engine off and also with engine idling. unfortunately it kept starting up every time I shut it off. I couldn't do it during crank, no start.

 

[SunlitComet]

Let me try again. Where in the wiring? On the side of injector wiring that had a red or white wire from fuse or the other side which have wires going to the ecm?

 

[chevykid91]

I think the problem may be on the ecm side, but I have to have a good day to trace the wiring back. If its the reading i got. I got them from going across each injector. With a dvom one probe on each injector terminal unplugged with ignition on. And back probing wires when running.

 

[chevykid91]

Found the issue it was the fuel pump relay. It wouldnt start on a hot and humid day. Thanks for all the help.