ongoing problem has mechanics stumped

TheEdgeofSanity · 09-06-2011, 01:47 PM

so, its been awhile. hello to those who remember me and hello to all of you who don't!

my car is still going with nearly 160,000 on the clock but I don't trust it too much anymore!

for over a year now, I've been having an issue where I will notice for a few days that my car seems to stutter when going up hills after driving for 30 minutes or more. After a few days of this getting consistently worse, it will finally start dying. It usually cuts in and out a few times then the rpms slowly drop and it dies. no codes being thrown or anything. If I try restarting the car, it may spit and sputter but won't start. If I leave it alone with the ignition off for 10-15 minutes, it will fire back up like nothing ever happened. I can drive around a minimum of 30 miles and it will do it again. Some other info includes that I always keep my fuel above 1/2 tank and I run chevron techron fuel system cleaner through my car religiously every 10,000 miles. I use good quality gas from stations that my parents get fuel from and never had any issues with.

The car will keep doing this process until I take it in for service. The first time, I had my fuel filter changed and my throttle position sensor changed. Mechanic said it was in all parameters for fuel pressure and he could not get it to die on his test run. It was fine for 6 months with no symptoms, then exact same thing happened again. Took it to another mechanic who also could not get it to do this (it seems to only happen on 50+ mile trips or in heavy traffic shorter trips) and he changed the fuel filter too. Both mechanics said my fuel pump is fine because when fuel pumps go out, they just go out and never start working again. I am at a loss. Someone suggested it may be related to the FPR but idk. please help if you had this issue and resolved it!

I forgot to say that the whole reason I am mentioning this is because it is happening again and I don't know what else to do than change the fuel pump which is big $$$ that I don't have!

MMGT1 · 09-06-2011, 02:33 PM

Crank position sensor bud. The 7X sensor at the back of the engine, not the 24X at the reluctor wheel. Replace the harness from the Ignition Module to that sensor while your there. Problem sloved....

MMGT1 · 09-06-2011, 02:36 PM

.... and before you ask, no. 9 out of 10 times it will not throw a code

SIUlero · 09-06-2011, 03:18 PM

Check your fuel pump relay...it may be overheating. Make sure it isn't corroded up and doesn't have excess resistance on the switched side. I had a problem like this at one point and it turned out the contacts inside my relay box had gotten weak and weren't making full contact with the relay all the time. I had to take the box apart and tighten them back up...haven't had a problem with it since.

TheEdgeofSanity · 09-06-2011, 06:14 PM

you know, the fuel pump relay issue seems plausible... i know they are only like $15 and easy to change so I might start there with it. it seems to fit the description of my issues

TheEdgeofSanity · 09-06-2011, 06:25 PM

are there any ways to test a crank position sensor?

a.graham52 · 09-06-2011, 07:48 PM

hows your tuneup?

MMGT1 · 09-06-2011, 08:25 PM

Yes, Tech II can scan for the output signal but it has to be acting up at the exact time that it is connected. What happens is the sensor has a plastic housing. Once it is heated and cooled so many times it swells and gets tiny cracks in it. Once the engine heats up, those little cracks open up and that skews the output signal of the sensor, messin with the ignition module, resulting in the exact problem listed. Pull the sensor and have a look at it. You'll actually be able to see where the sensor is swolen at the end that sits inside the block exposed to the heat. The connector is exposed to a shit ton of heat back there and the wires from the sensor have actually been known to fuse from the heat, but that one will cause a complete no-start situtation. With 160 on it its right in line mileage wise to what Ive seen myself

Papa Rad17 · 09-08-2011, 04:22 AM

I'm just going to toss this out there... Lower intake manifold gaskit? I hear that's common with your engine. Sorry if that's really nooby. The other thing that came to mind for me was something to do with timing...??

TheEdgeofSanity · 09-08-2011, 01:35 PM

well, changed the fuel pump relay out... hasn't died yet, but I haven't gone too far either. At NAPA, the guy was saying my tank may have alot of sediment which is clogging up the screen filter on the fuel pump itself... seems possible. I just am at a loss. I am fairly sure its fuel delivery related because I don't hear the fuel pump running while its broke down and I am trying to start it

MMGT1 · 09-08-2011, 06:47 PM

Unless you've been getting your fuel from a wrecking yard, I doubt you have that problem. If your pump was that dirty you would also have a fuel guage issue. Meaning the sending unit on the side of the pump would be fouled and not reading properly. The issue as you described it still leads me to the crank sensor bud. Get it out for a good 45 min drive on the hwy and see what happens.

MMGT1 · 09-08-2011, 06:49 PM

To add, that sensor is a 25dollar part from the dealer man, its a cheap fix

TheEdgeofSanity · 09-13-2011, 10:27 AM

alright, well it hasn't died since changing the fuel pump relay but I will have my mechanic check out the crank sensor. where can I find it at? how hard is it to install?

MMGT1 · 09-13-2011, 11:42 AM

GM dealer Part #10456555. It lists' up here for around 43 bucks. Its in the back of the block(side of the block looking from left to right) closest to the firewall. You can follow the connector from the ignition module down to the sensor. Easy to change, just make sure that the top of the sensor is very clean before you pull it out. Use dielectric grease on the new one when you install it, on the seal