Hello. I posted once previously about some issues I was having that I thought were fixed by changing the CMP sensor, but it seems that this was just a temporary fix because the symptoms have returned: car dies at idle or when slowing down at a stoplight or to make a turn.

This is a 2001 2DR 2WD Blazer with a 4.3 "W" engine.

The engine seems to run very well right up to the point that it dies. I bought a fuel pressure tester and I'm getting 60 - 62 psi at key on, engine off. When I start the engine it holds right around 55 psi.

As soon as the fuel pump stops running after the engine dies or I turn the key off, the pressure drops immediately to zero. Just as fast as it shoots up to 60 psi initially, it drops that quickly to nothing.

I noticed that the fuel pressure didn't change immediately prior to the engine dying, and in fact it went back up to 60 psi when the fuel pump kept running for two seconds after the engine stopped.

I'm aware of the fuel pressure diagnostic procedure, but before I spend the money to buy the shutoff valve for the fuel line I wanted to check here and see if my symptoms are something that always points to one part of the fuel system over another.

I looked down into the throttle body and could not detect any gasoline smell. The spider looked pretty black and there was a coating of oily black grease on the bottom of the throttle body butterfly valve, but I don't smell fuel anywhere in the engine compartment or underneath by the fuel filter, or back under the gas tank.

I would really like to upgrade the fuel spider and add a new FPR as a part of that, but I can't afford to do that if the problem is really in the fuel pump. I replaced the fuel relay since it's so cheap, and I have a new filter ready to go on when I begin work.

Any help or suggestions are appreciated. Thanks!!!

 

Sorry to bump this, but so far no one has weighed in so I thought I'd bump it once to see if anyone bites.

I would also like to add that I replaced the fuel filter this morning and I noticed that all of my pressure readings went up by a few lbs, and the leak down after shutting off the engine slowed down noticeably. Before i changed the filter the pressure would immediately drop to zero when I turned the key off, and now it drops down immediately to about 10psi and it takes about 30 more seconds for the gauge to reach zero.

If there was restriction because of a dirty fuel filter and the leak was in the fuel pump, wouldn't the system leak down faster (or just as fast) if you removed the old fuel filter that may have been restricting flow back to the faulty check valve upon shutoff?

I also noticed that I've been leaking coolant every time I run the engine since my initial problem surfaced, and today I found a big crack in the plastic end tank on the driver's side of the radiator. So I will be replacing that as well.

If no one has an opinion on what is the likely cause of the fuel pressure leak down, I guess I will go pay $60 - $70 for the GM fuel line shutoff valve tool so I can pinpoint the problem and start working on it. I just hate paying that much for a tool I may only use once.

Thanks!

 

I am sure that no one has weighed in due to the VERY common problem you are describing. There are many threads on this very subject all over the forum. If your fuel pressure is bleeding off, you have a leak somewhere in the system. If a visual inspection does not leave any clues, you have to start opening things up and do some more visual inspection. You likely have a blown FPR under the intake.

Check out the Tech Article section for the 96+ fuel system diagnosis thread and follow the steps there to determine the location of your leak.

The FPR is on the back of the spider all the way at the very back of the upper intake. You likely will not notice it leaking as it would just drain into the closest cylinder. That said, your problem may likely be the check valve in the tank. But that should not cause your truck to die. That sounds like an entirely different problem.

 

Thanks for the reply. I've read hundreds of posts about this subject on many different message boards, but there are many instances of people posting their problems without coming back to post the resolution once it's fixed.

I agree that the FPR is probably a good place to start since it's only about $50 to swap it out for a new one. I took off the throttle body tonight and cleaned it thoroughly along with the IAC, but I stopped because it started to get late and I couldn't find the right tool to disconnect the fuel lines at the fire wall before going any further with the plenum removal.

I am going to attempt to clean the poppet valves as per the GM tech bulletin since I just had a baby and the MFI spider isn't in the budget. Thanks again for your help and I will follow up on here if the new FPR fixes the fuel pressure problem.

 

OK, so I changed the fuel pump and the problem with the leak down has been eliminated. It now holds pressure after I turn the key off.

I also changed the radiator because of the crack in the plastic end tank on the driver's side, and I'm no longer leaking coolant.

However, I am still having a problem with it stalling on me after it warms up. When I did the test drive after the fuel pump replacement, I drove about 15 minutes and then stopped for gas. When I went to pull away it bogged down for a second or two and then quit on me. I coasted into a parking lot and restarted it. It started instantly. I then revved the engine and as the RPMs fell they just went all the way to zero.

It would start up right away and then die immediately, just like before. It was 4am and pouring rain, so I just sat there and listened to music for about an hour until things had cooled off some, and then I started it up and drove all the way home without any problems.

I have replaced the coil, ICM, distributor, fuel filter, cap and rotor, plugs, plug wires, fuel pump, fuel pressure regulator, air filter, and radiator.

I have cleaned the IAC valve, MAF sensor and throttle body.

I just now pulled the first O2 sensor and replaced it with the one after the catalyst, but besides seeming to run a little bit better it died after about 15 minutes of idling in the driveway and a quick trip around the neighborhood. My next step will be to replace the second O2 sensor with the one from after the catalyst to see if that changes anything.

I'm not going to throw any more parts at it and plan on taking it to a Chevy dealer for a diagnostic, but does anyone have any thoughts on this in the meantime?

2001 2DR, 2WD 4.3 (W)

Thanks!

 

Have you cleaned the EGR valve?

 

Yes, I forgot to mention that one. I pulled it off again the other night after my test drive just to double-check it. The pintle moves freely and there doesn't seem to be much carbon in there at all. It looks clean. Black, but clean.

I should also mention that I keep my code reader hooked up the entire time and I've never gotten a code throughout this process (besides when I messed up the timing on the distributor install).

 

What brand of Fuel pump did you buy?

 

It was an AC Delco, and I believe the model was MU1755. I got it from rightnowautoparts.com for $248 including next day shipping. The dealer quoted about $495 for the same model number.

I just got back in from rotating the other O2 sensor to the position behind the catalyst. No improvement. The car died a few minutes after reaching operating temp.

I know that test doesn't prove anything necessarily, but I figure if the post-cat O2 sensor doesn't affect how the engine runs then rotating the sensors might tell me if I have one that's bad.

Since the original issue also included the power cutting out to about 200 RPMs when I was on the freeway doing 60mph, and then going back to full power after about 10 seconds of hanging around 200 RPMs, I want to exclude the IAC valve from being the issue. Is that faulty logic on my part?

Is it possibly the ECM, or would that tend to fail less predictably?

 

I just wanted to follow up and say that the problem appears to be fixed. I also want to provide a thorough synopsis for people who may be having the same problem. I will try to list the symptoms, fixes and results.

SYMPTOMS

*Stalling at or around idle. The first time it died was when I was pulling into a driveway. Would always start back up immediately and die just as quick. After sitting for a few hours you could drive for a bit before having more problems.
*Hard starting (8 or 9 cranks instead of 2 or 3)
*Bogging down at freeway speeds (RPMs dropped to ~200 @ 65mph, then after about 10 seconds of coasting full power would be restored)
*Bucking and stalling when pulling away from a red light
*Problem surfaced in July, and usually only during the hotter part of the day. I could drive to work in the morning without issues, but could barely make it a few miles in the afternoon heat on the way home.
*Never received a DTC or MIL from the stalling problem
*Would not hold any fuel pressure after the engine was turned off. Fuel pressure readings were good with the pump running.
*Coolant leaking (later found a crack on the driver's side plastic end tank)
*When it wasn't stalling or idling rough, it seemed to run perfectly normal.

FIXES

*Driving with two feet. At first this would keep the car from stalling at a red light. Eventually this stopped working.
*Replaced Ignition Coil
*Replaced ICM after it tested bad at O'Reilly, but it later tested good at Autozone when replacing this didn't help. (multiple tests are good, but a second opinion doesn't hurt either -- i think the guy at O'Reilly didn't know what he was doing)
*Cleaned EGR
*Cleaned throttle body
*Cleaned IAC valve
*Cleaned MAF sensor
*Tested battery - Pass
*Tested alternator - Pass
*Replaced fuel pump relay
*Replaced PCV valve
*Replaced spark plugs and wires
*Replaced fuel filter
*Replaced distributor cap and rotor
*Replaced camshaft position sensor (this seemed to improve things, but I was mistaken)
*Replaced distributor
*Replaced air filter element
*Replaced fuel pressure regulator
*Replaced fuel pump (re-wired existing harness to new style, installed new ground wire on tank)
*Replaced radiator
*Replaced serpentine belt
*Replaced radiator cap


SUMMARY OF RESULTS

I made a few big mistakes during this process. First of all, I should have bought a fuel pressure tester before anything else. Secondly, I wrongly assumed that the problem was in the ignition system since it seemed to correspond with higher ambient and engine temperatures. Since I wasn't getting any codes, I took the wrong path of trying to "tune up" my way out of it and then later just started throwing parts at the problem.

Sure, I don't think a new coil, ICM or plug wires will hurt me, but stuff like that adds up and I think it's better to spend your time and money on the real issue first. I've got a distributor sitting on my shelf that I'm not going to return for the $25 core charge, because it now appears that I would be selling them a working distro for chump change and I'd rather just have a spare. I could have used the $50 I spent on the FPR towards buying an MFI spider. Throw a few of those other unnecessary parts in there and the MFI would be mine.

The list of fixes above is roughly in chronological order. I believed I was seeing positive results with some of the things I changed out, like CMP sensor and distro cap, so it wasn't until I was towed home for the second time that I decided not to go more than a mile from home until I was sure the truck was fixed for good. These things that I thought were helping also kept me on the internet for countless hours and at the parts store looking for the next $30 component that would be the final missing piece of the puzzle.

I'm not sure when I first noticed the radiator leaking fluid, but I think it was after I had already broken down a few times. Stupidly, I decided that I would replace the radiator once I figured out what was going on with the engine so I wouldn't be sinking hundreds of dollars into it if there was a much more serious problem that required me to spend my limited budget elsewhere.

I think the radiator was the problem the entire time. Or, actually the radiator cap. I replaced the radiator and the fuel pump in one long night, and everything else in the list above had already been completed at that point (besides radiator cap and drive belt). I forgot to buy a new cap when replacing the radiator because I thought it came with one, and when it was finally installed the parts stores were closed so I just went with the old one and took the truck out for a test drive to see how the new fuel pump and radiator would affect the problem.

When I left my house on the test drive I stopped at a gas station a few miles down the road to fill up. As I left the gas station the car bucked and stalled on me. I couldn't believe the problem was still there, and I started to think an O2 sensor was bad. A few days later I rotated all of the O2 sensors around to each position to see if it would run differently or maybe give me a catalyst or O2 code. That didn't help.

At this point the truck would start up when it was cold, and I could drive it around the neighborhood a few times and let it idle in the driveway until it would eventually stall. The amount of time it ran and the operating temperature it reached before stalling seemed to get lower every time.

I told my wife yesterday that she wouldn't have to drive me to work much longer, because if I couldn't fix the problem I would drive it to a dealership and pay the diagnostic fee. So last night I took the battery and alternator to Autozone to have them tested since I noticed my dome light kind of pulsating in time to the engine a few days ago. They both tested OK, so I told the guy to go ahead and give me a drive belt and a radiator cap since I was already there.

I installed the battery, alternator, belt and rad cap when I got home, and to my surprise the truck didn't die like it had before. The radiator cap looked like the original and I've got close to 100k on this truck. Not sure if the previous owner did much of that stuff, but it doesn't look like it.

Another thing that I made a point of doing this time when I started the engine, was not to put my foot on the gas or put it in gear until it had a chance to idle for a while and go through its self diagnostics. I was always eager to pull the truck out of the garage so the fumes wouldn't go in the house and harm my new baby, so I don't think I was giving the truck a chance to set the idle and all that stuff when I reconnected the battery the other times.

So the truck sat there idling in my garage for at least an hour while I looked for any sign of a vacuum leak or a blown gasket. It stumbled a few times for just a moment or two, but the engine never died so I turned it off and went inside for about 1.5 hours to eat dinner and wash up.

When I came back out later to do a test drive, the engine fired up immediately with just the slightest turn of the key and didn't give me any problems through 50 miles of driving around town and on the expressway. I made up a few errands to run and stopped at three or four places without experiencing any troubles.

So I'm now thinking that the drive belt may have helped somewhat, but it was only about 4 years old and didn't look terrible. I think the difference was the radiator cap. I believe that the old one leaked air into the cooling system, which caused the coolant's boiling point to drop and build up enough pressure to blow a crack in the plastic end tank. Once the radiator was breached, I think the engine wasn't getting cooled properly and that's what was causing it to die. I replaced the radiator but used the old cap (DUMB), so I never realized an improvement until I got rid of it.

The frustrating thing about this process has been that I never got any DTCs or MILs to point me in the right direction. On the bright side, when I stopped at WalMart last night during my test drive to pick up some Sea Foam, I walked out and felt a surge of pride at seeing my Blazer parked there and ready to go. So much different than the past few months of seeing it in the garage with the hood open and a towel underneath to soak up the leaking coolant.

I scraped my knuckles, cut my hands and mixed my blood with his (oil, coolant, AT fluid) during countless hours of trying to resolve this problem, and now that it seems to be running well again I want to keep it more than I want a new car. Not to overly anthropomorphize it or anything, but it's like we're blood brothers now and I feel a renewed commitment to my plan to run it until it dies and I can't fix it anymore.

I know this post is very long, but hopefully it will help someone. I am going to get my coolant flushed and filled during lunch since I heard some gurgling from the heater core after putting in the new fluid. I added some Lucas Oil transmission stuff last night, and I'm going to Sea Foam the intake and crankcase when I get home from work today.

One last tidbit of advice: don't overtighten the nuts that go on your fuel line hold down bracket on top of the fuel meter body. Those two studs are anchored in plastic and are easy to strip out. Everything feels tight right now and the fuel lines aren't moving, but I will now be doing the MFI upgrade for sure in the next month or so. That was about a $300 mistake, which my wife thinks I did on purpose to get new injectors. If I wasn't dumber than I am sneaky, it might be a good theory.

Cheers.