HELP...8.1 Vortec acts like flooding

[lgavitt]

Hey guys. I've got a slight problem I'm hoping someone here can help to find and understand.

I've got a 2001 silverado 3500 crew cab with and 8.1 Vortec. It acts like the classic carb. flooding scenario. The more you mess with it while its flooded, the longer you have to wait for it to unflood, so to speak. It's been doing for a while as I've been trying to narrow in on the problem. Follow this scenario, and you understand the symptoms.

I'm driving along doing fine. It dies. No noise, smoke, shimmy, nothing. Just dead. All electical still works, just no motor. If I wait and coast in OD, it may restart like pushing it off (it is an automatic), rarely. If it doesn't restart, I pull over and wait a minute or two and it starts fine.

next time.

I'm driving along doing fine. It dies. I pull over and wait a minute or two but fail to get it started (should have held the key a sec or so more or whatever) but in any case no start. I try to force the matter with another attempt. Spin...Spin...Spin, no good. But now I have to wait even longer because I spun the heck out it. If I don't wait long enough, I have to extend my wait even more. This seems to be progressive. The more I try, the longer I have to wait. Finally I wait long enough and it starts just fine, like nothing ever happened.

I drive to work about 30 miles each way. It almost always does it in about the first 3-5 min of driving, then no more until I park it for a while. Then we start all over again. Sometimes, it does it more than once, but not normally. Rarely does it not do it. Temperature, humidity, electrical consumption, etc... doesn't seem to have any effect on it, good or bad.

Occassionally, I have the same problem when I attempt to start it from being parked. If, for whatever reason, it don't start on the first try, I'm playing the wait game again.

I've changed plugs and fuel filter. Filter was clogged. I don't smell any additional fuel when it happens, but I'm not at the intake either.

Any ideas? suggestions¿ comments?

Many thanks in advance.

Lee

[rjeffery]

Sounds like crank position sensor. I think it is a common problem on the 8.1s. Also, beware - they like to break off in the engine, so I would recommend having a dealer do it, if you determine that is indeed the problem.

[lgavitt]

Thanks for the reply.

Hmmm. I Didn't know that part existed. Learn something everyday. Not sure how it would do it, but you know; I remember (back in the day) when I learn about the "Hall-Effect Transistors" in the newer distributors. Like to drove me crazy, till I learn of that one. The only thing consistent about the sucker was that I knew whatever was wrong, wasn't fixed yet. I went through three computers, at $300.00 each, until I found a mechanic that knew what he was doing. It was a lousy $10.00 part, the "Hall-Effect Transistors".

For educational interests.
What does this sensor do, look for, or adjust? Besides the obvious, hahaha.

For troubleshooting.
Is there anyway to check or atleast adjust the confidence level on the crank position sensor. Something I can look at when it dies? Check for? What about diag codes? If so, how would I go about kicking it into diag mode?

Additionally.
Would the crank position sensor going bad cause my wait time to be proportional to how hard I try to force it to start, i.e. keep spinning it until it starts (which it won't start, only spin)? Because there is now doubt about it; the more I try to force it, the longer I have to wait. That pattern isn't random. I would expect a position sensor to provided random results. Maybe spin...spin...stop spinning...start. And then Maybe spin...stop spinning...start. But in my case, spin...spin...stop spinning...wait...wait...start. And then spin...spin...spin...spin...stop spinning...wait...wait...wait...wait...start. I've tested this this start pattern extensively, because at first I thought it was electrical. I had to turn everything off, wait a sec. and then it would start. But I've eliminating the need to turn everything off. It doesn't change anything, I only thought it did.

[rjeffery]

I belive the sensor reads the position of the crankshaft and relays it to the computer which adjusts the timing ect.

Lots of good info here: http://www.dieselplace.com/forum/sea...archid=2717867

[spackelman]

I'm having the same problem with my 2002 8.1.

Doesn't stall evey time, but it does stall. After a few attempts to start, it finally does start. There is no pattern except that is usally stalls within 5 miles of driving from a cold start.

From other forums, it seems the problem is the crankshaft position sensor ($100) from GM.

However, I cleaned the MAF with CRC MAF spray cleaner.

Since the cleaning, it has not stalled (about a week).

Not sure if there is any connection, time will tell.

[lgavitt]

Stalling wthin 5 Miles of cold start. Now that's quite similar to what I'm seeing, except for the pattern. I've been fighting mine for about 6 months now trying to narrow in on it. That's how I've determined there is a pattern to mine.

If I travel 5 miles, I'm 90% guaranteed it will stall. If you were like that and you've gone a week without doing it, then it sounds like you may have hit on it.

I am interested in trying the spray cleaner; however, I'm not familiar with the acronyms: MAF and CRC. Could you tell me a bit more about it. What the acronyms. Got any advice for the process?

Thanks

[spackelman]

CRC is a mfg of industrial / auto chemicals
Red / white / black spray cans on the shelf at your local auto supply.

MAF = mass air flow sensor.

[lgavitt]

MAF...mass air flow sensor...Now that could cause the flooding like symptoms. Cleaning, or replacing, that guy could make a difference.

Unless I'm missing something. Can anyone point out a fault in this theory¿


Later Edit......

For those interested.
After researching info on this, I have found that the crank position sensor may very well be the culprit. As the motor is spinning, fuel may be being dumped into the motor, however, it isn't getting fired on because of the sensor going out. The result is "Flooded." Hence the wait time being porpotional to the efforts to start the motor. I'm going to change it and will post back later with the results.

[fillupread]

You need to determine if its a lack of fuel or a lack of fire next time it dies. Start there.

[spackelman]

My truck stalled today, about 5 mi from a cold start this morning.

Was doing about 45 mph. It re-started by simply keeping it in gear.

Blows my theory about a clean MAF sensor. Wishful thinking I suppose.

Need to get a new crank pos sensor.

[lgavitt]

Spackleman.

Yesterday I went and dropped the money on a scanner to check my codes. Guess what popped up. Crankshart Position Sensor. Go figure.

This is what I understand from some further research...
Chevy had thousands of these things go bad. Almost to the point of a recall; however, their repair database and a third party's database didn't match enough to warrant the expense of a recall. The third party showed higher than the Mfg., so is was not worthy of the expense. Again, this isn't fact that I can prove, so take it to be what I understand.

This doesn't mean that it is source of our problem because I've seen other posting and places where people have change it and problem solved and some change it and no difference. The only thing I'm confortable with right now is that mine is probably bad (as per comparision of symptoms with postings and the scanner ID) and needs changed. I mail ordered the part the other day. $94.00 and some change.


Reminds me of Jerry Clower. Shoot up amongst us. One of needs some relief...lol. Will the part fix it, or will it begin to drive me crazy. We'll see.

PS. I also found that the CPS works on the Hall-Effect design. Real flacky when they start to go bad. They may work one minute and not the next. Their detection mechanism is based on magnetism.

Oh yeah....Cam sensor is another one that seems to be related to the same symptoms. Seen alot of postings about changing the cam sensor fixed their problems.

[rjeffery]

Be careful when changing it, I hear those things like to break off in the engine.

[fillupread]

Does anyone know if the crank position sensor was an issue on the 5.3?

If it does break off you can use an old trick we used on the quad 4 crank position sensors. AIR PRESSURE! Remove the oil filler cap, cram a rag in the opening and the jet end of a compressor nozzel. As you add some air pressure to the engine and POP! It sounds odd but trust me it works.

[rjeffery]

Originally Posted by fillupread

Does anyone know if the crank position sensor was an issue on the 5.3?

Havn't heard of it being a problem on any engine but the 8.1.