Killing ICM's?

[98_k1500]

Yea me too lol.

 

[gmcyukondriver]

Sorry dude, I'm not going to beat on my truck to try to diagnose something.

I'm going to go get a test light as soon as I can use my dad's truck. Then I'm going to check the power at the relay and make sure that the computer is telling the pump to prime when I turn the ignition on, it should light up for 2 seconds when the computer sends the signal. If it doesn't, it's either a problem with the ECU, or the wiring from one to the other.

If it DOES light, then I have to crawl under and figure out a way to test the wires at the pump for power and ground. Keep in mind, this is on a Yukon, not a truck, so my tank isn't as easily accessible (I can't just pull the bed off). Assuming I have power there, then it's confirmed the pump is bad and I'm going to replace it.

And like I said, I just filled up, and I'm not going to run $80-100 worth of gas out the motor at idle just to make the tank lighter, sorry. I'd rather take it to a shop and let them deal with it than to do that. I appreciate the input, but I was hoping someone would be able to tell me where the pump grounds on the body/frame so I could make sure that ground isn't corroded. I guess I'll just have to climb under and do some wire tracing.

What's weird is that it hasn't died on me while running, it's only been a starting issue, but I guess it could still be the pump.


This video is along the lines of what I'm going to do first:

http://www.youtube.com/watch?v=McnXLcJNVfI

 

[98_k1500]

Check to see if you have a 3 wire oil pressure sending unit.

 

[great white]

His recommendation to listen for the pump running is a valid one. Knocking the tank is a common way to see if the motor is just plain gone or intermittent. A pump on its way out (but not totally gone) will sometimes run and sometimes not depending on where the rotor/commutator ended up when it last stopped. Knocking the tank gives It a little "bump" to get over the initial start up high amp draw. You dont dent the tank, you just give it a couple good knocks. The pump still has to be replaced in this case, it just gives you a little confirmation of what's going on.

Checking for power is also part of the troubleshooting process.

If power and pump running but no pressure, it could be something unusual like a bad regulator bypassing straight back to the tank.

Unlikely, but possible.....

 

[gmcyukondriver]

Ah, ok, see giving it a "bump" is different than beating the hell out of it. I'll give that a shot.

Yes, I should have a 3-wire oil pressure sending unit, but if that was bad, then my oil pressure gauge would also be having issues, wouldn't it? As far as I know, it hasn't had any.

Thanks for all the help guys, I'll keep testing and letting you know what I find. Right now, it looks like it might be the pump, which means I would probably replace it next week, I just don't have time right now. I also would like to do some research into using a pump for a Vortec truck, because I'm supposed to have slightly higher fuel pressure anyways, and that would be able to handle the extra demand a lot better than a TBI pump, which barely keeps up with the stock motor.

Anyone know if this is possible or how easy it is, to use a Vortec fuel pump on a TBI truck?

 

[gmcyukondriver]

Well, I used a test light on it, and narrowed it down. It's gotta be the pump. I checked the underhood fuse block where the fuel relay plugs in. It has constant power where it should. I also checked to make sure the ECU is sending the signal to the pump to prime when the ignition is turned on, and it is. The grounds are also good.

Yes, I have a 3-wire oil pressure sending unit. I tested the powered part of the connector, and it has power. I used a paper clip to jump it to the pump wire, and listened but didn't hear the pump prime, and didn't get any fuel pressure.

Tomorrow I'll knock on the tank and see if that does anything. However, considering this IS the original pump from a 1995 GMT400, I'd say that I've outlasted most.

 

[Ruger_556]

Tomorrow I'll knock on the tank and see if that does anything. However, considering this IS the original pump from a 1995 GMT400, I'd say that I've outlasted most.

Mine is original

 

[SCOTTYINWV]

Jdyates is running a tpi pump from a 92 (iroc iirc) Camaro and it is supposed to be an "upgrade" from a stock tbi pump. It can be installed into the stock sending unit also.

 

[Darkrider]

Jdyates is running a tpi pump from a 92 (iroc iirc) Camaro and it is supposed to be an "upgrade" from a stock tbi pump. It can be installed into the stock sending unit also.

Beat me to it lol...but yea i was gonna suggest a Camaro pump as well.

 

[98_k1500]

Sorry about the confusion about beating on the gas tank lol. If you get someone to cycle the key on and off rapidly while you bang on the bottom of the tank, it will probably run properly for a few starts and then stick again. No need to leave dents in the tank or anything, but when you are laying under one, its hard to hit anything very hard. You will probably need to hit it nearly as hard as you can, not much room under there to get much of a swing on it. The vibrations from you hitting the tank can move the fuel pump off the bad spot and get it started. Good luck with it. I would look at the GPH rating of the pump and replace yours with something similar. One capable of a little more pressure is fine, but if the GPH of the pump outruns your regulator's ability to return fuel to the tank, fuel pressure will spike when you let it idle and drop substantially at WOT. This would cause all kinds of funky and unusual issues.