I'm about to burn this G^%&*DAM GMC pick-up

Vehicle: 1994 GMC Pick Up .... 5.0 L

Problem: working like a crap bucket

Symptoms: feels sluggish while driving, sputters and bucks while stopped in " DRIVE" with foot on brake ( will come back to decent idle when this happens if I quickly shift to "NEUTRAL"). Five minutes later, it all starts happening again.

Took my vehicle to a machanic with 30 yrs GMC experience. It was determined ( and I did see the parts) that dist cap, rotor button, plugs, fuel filter and air filter were all in desperate need of replacement.

After the job was done, I took the truck and it worked like a new vehicle for about 30 miles of "in town" driving. Then, it quickly turned to crap again ........and this time the problems, although similar, were much worse that the original problem that I took it in for in the first place.

Symptoms after all the tune up stuff was replaced :

1) intermittantly sluggish 2) voltage hand goes crazy ...flicking back and forth from 10 volts to about 14 volts. Lights, dash lights, blower motor etc all dim out when this occurs. ( I can level this off back to a normal reading while moving if I pop the thing into NEUTRAL and bring the RPMs upto about double or more of idling rpms. It then setttles down to normal. Five or 10 minutes later it all starts again. 3) Now, the truck won't even stay idling when in neutral or when stopped in "DRIVE" with foot on the brake. I've also noticed that if I rev the engine while in "PARK", the indicator hand on the speedometer shoots up to the 20 MPH mark. None of these "after tune up symptoms" were there before the tune up.

Back to the shop I go. Diagnosis: Alternator faulty. New Alternator installed ( Bosch) 100amp. I leave the shop ...........same troubles again.

Back to shop again. Diagnosis: Oxygen Sensor needs replacing. I leave the shop .......same crap still happening.

The mechanic ( who also owns the shop) has now spent more than 20 hours trying to solve this problem. He's told me that no matter if it costs him a foutune in time he will correct the problem at no more charges to me......... but we are both still scratching our heads in bewilderment.

Now here's the really strange part. If I let the truck sit all night it will start and idle in the mornings with no problem at all ....even at minus 10 celcius. I've gone as far as letting it idle for 25 or 30 minutes while sitting in the driveway.

As soon as I start moving ( after about 30 seconds to a minute) the whole nightmare resurfaces again....... and as usual it comes and goes in intervals of from 5 minutes to 10 minutes.

Keep in mind: before the tune up the only problem was sluggishness and the fact that it died out while in drive with foot on the brake ....for example ...while slowing advancing through a drive -through line at the coffee shop. After the tune up, all hell broke loose and I have the original symptoms plus the new ones I listed.

We are both tearing our hair out over this. Any suggestions ? All suggestions and thoughts would be appreciated.

Thanks !

Reply to
Dairmada
Loading thread data ...

This is a GUESS..........

Only a Guess........

In case of a real need of help contact a better guesser..........

------------------------------------------------- Carbon buildup in the intake and EGR passages have been accentuated by disconnecting the battery and setting the controll module back to factory preset perameters for a NEW engine system. The controll module is now running on factory programming for an engine with NO miles on it and all hell is breaking loose cuz it ain't figured out why it can't gain controll of the emissions......... sorta...... kinda....

(synopsis)

yer trucks brain is convinced it's young at heart........but them days is long gone fer ever.......

(suggestion)

try cleaning the "top end" and EGR system of carbon and then do a couple of "drive cycles" to allow the computer to remember it ain't as young as it once was.

~:~ MarshMonster ~:~ air leaks caused by carbon keeping things from sealing correctly will reak havoc after battery disconnect resets the computer on a high mileage or neglected vehical.

Reply to
MarshMonster2624

Sounds like a voltage or computer problem.

Serpentine belt glazed? Belt tensioned weak? Heavy drag from one or more accessories? Engine running starter draw? Bad negative post to chassis ground? Bad cell in the battery? Overheating computer? Bad connection at the computer? Faulty positive or negative ground?

Reply to
Shades

Bad Ground dude.

Use a DC volt meter to check voltage between the NEGative battery post, and critical "ground" points around the vehicle (alternator, starter, ignition control stuff, dome lights, etc). The voltage "potential" across these two points should be almost, if not, ZERO. If it's not, your entire electrical system is literally operating in its own electrical "plane", and therefore can never work together, if at all.

HOWEVER, should you decide to burn the G^%&*DAM truck, the faulty fround would make for a more sudden explosion of the battery as it could only fault internally.

BT3

Reply to
BT3

Reply to
Sigwings

Bad cell in battery? My 01 Dodge Ram started doing just about the same thing. Dealer replaced the battery and all was well. Dealer said newer trucks run just about everything off the battery now and the alternator just charges the battery up. (His words not mine). Anyway if you get it fixed please let us know. My Dad has a 90 GMC that runs like it's still new but I'm keeping a list off all problems I find here and their solutions for him just in case.

Bob

Reply to
Bob M

alternator

He wasn't off in his statement, the battery performs as a pseudo surge protector for the system. You turn the lights on, or off, step on the brakes etc, you get little voltage drops and spikes, the battery smoothes them out to protect the ECM and other computers on a vehicle. It was this surge aspect that was a guaranteed replace the ignition module on Fords if the battery is disconnected while running. That's another reason its a good idea to shut a vehicle of before hooking up or disconnecting jumper cables when its the jump vehicle as well.

Whitelightning

Reply to
Whitelightning

Howdy Again, People !

Well, the nightmare continues !

As luck would have it, while the truck was in the shop again today, the snap-on electrical rep. showed up attempting to persuade the owner of the shop ( who is also my mechanic) to buy one of their new 10, 000 dollar scanners. In an attempt to demonstrate his wares he allowed the shop to analyse my truck with this new piece of equipment. THE SCANNER SHOWED EVERYTHING IN THE VEHICLE TO BE WORKING PERFECTLY ! Earlier that day, we also took it to the GM dealer and had it analysed on their equipment ....everything checked out ok there as well. However, the problem still exists !

As I said in the original posting, this apparent electrical drop -off ( which is intermittant but very frequent) stops, and the rpms and voltage hand return temporarily to normal, there is still a surge in the engine. Once the surge starts, it is quickly followed by the electrical power fluxuations. Again, when all this happens, if I stamp on the accelerator everything electrical picks up again....... but the rpm surge can still be felt ......it's like a perfectly timed miss.

There are about a dozen licenced mechanics involved in this issue now from Gm dealers and private shops .....all are scratching their heads and all are extremely curious as to what the hell is going on. They are all so freakin' curious about this issue that all the advice asnd suggestions are coming free of charge from everyone !!!!! ( lucky me ) !!!!!

Well, we are all still baffled ...completely ! Mechanics are laying awake in bed at night thinking about the symptoms ...and you can include me in that pile too !!!!

Back to the shop I go tomorrow .....my mechanic and collegues can't wait to go at it again !

Thank you all very much for your suggestions and thoughts ! We are very open to every suggestions and thought all you posters can come up with. I am printing these replies and dropping them off at the shop each morning and my mechanic is appreciating all the input as well. If anyone has more suggestions ..... WE ARE ALL EARS !!!!!!!!!

Thanks again to everyone !

Reply to
Dairmada

So has everything all of us suggested been eliminated?

Reply to
Shades

Well, like everyone else who has a job, I cannot be there 24/7 to verify all they are telling me but I completely trust my mechanic as he is a friend as well as my mechanic. From the posting print outs I've given him he told me tonight that he's checked ever suggestion that's come his way. This guy is very knowledgable and automotive repair is all that he lives for. He works morning , noon and night 7 days a week and has an excellent reputation among his peers.

Right now he is starting to wonder if this problem may relate to the NEW oyygen sensor and is going to re-examine it and the wiring harness area related to it in the morning .......afterall, we are right back to square one !!!

I'll keep you posted !!!! .............. and thanks again !!!!!!!!

Dairmada

Reply to
Dairmada

Burn it!

LOL...jk

If all the suggestions have been gone through, its probably something so obvious and/or small that its never thought of and will probably be found accidentally.

Reply to
Shades

how about the starter? Doesn't all current run through it? My Vette would loose power, changed out the starter and all was well...

Reply to
Gordon

Hello again, Advisors !!!! (LOL)

As I last mentioned, the next move was to look at the newly installed

4-wire Oxygen sensor. I drove to the shop ( about a mile from my house) and by the time I got there the truck was acting up again. ...... as in it would die if I let it idle both in park or in drive with my foot on the brake. They disconnected the oxygen sensor and the bloody thing (truck) started idling pretty normal. THey told me to drive it like that ( with sensor disconnected) for the day to see what happened. Well, the surging, bucking, hesitation problem completely disappeared although my senses still detect a very slight rough idle while stopped at a stop sign ...but not enough to even give a crap about.

So, at this point ( because I need my wheels) I am using the truck with the O2 sensor disconnected.

Because of the problem I've been having, I find myself watching the voltmeter on the dash more than I look at the speedometer......and I noticed that ( and I assume this is normal) when I turn on the blower motor for the heat in the truck, the voltmeter hand drops back one and a half or two notches, I guess because of the draw of the blower motor. However, I also noticed, and it doesn't appear to be right in my mind's eye, that when I turn on the blower motor and the voltage drops a tad, I can rev the engine all I want but the voltmeter hand does not move up the scale at all...... not in drive and not in park. It just sits still at the point where it dropped back to. It doesn't even attempt to move when RPM's are increased. IS THIS NORMAL ? ( Keep in mind I installed a new 100amp BOSCH alternator after the original mis-diagnosis.)

I certainly appreciate the input you folks have been giving. I don't know if these additional bits of information could help in any way but I know that all clues could be helpful in this situation !!!!!

The handful of local mechanics who are now involved in this issue ( and myself) have also reached the conclusion offered by " SHADES AT DOT" that when the problem is found it is going to be so silly and or stupid that we are all going to laugh at each other and take turns kicking each others butts !!!! LOL

Our ears are still open to all input .........and again, thank you very much to each and every one of you !!!!!

Dairmada

Reply to
Dairmada

Sounds like a fuel pressure problem, or computer problem. Have tech. look at computer data while this problem is happening. Good Luck.

Reply to
jsc157

-------------------------------------------------

Having only the symptoms that you listed in the first post (start of thread) and the knowledge of the FACT that you're tech has checked EVERYTHING that the group has suggested...............

including the carbon buildup..........

i would like to gander one more guess............

lockup converter on the tranny ain't cutt'n loose like it's sposed to.

this is a guess, only a guess, and does not expressly represent the only guess i have.

~:~ Marsh Monster ~ain't never,ever,never.......seen no $10,000 scanner.......~

Reply to
MarshMonster2624

I'm not sure exactly how you're wired up, or what size wires are used for your system, but until somebody with more experience with YOUR vehicle comes along ....

The voltage drop indication just means something is using electricity on or near the same point (electrically) as the meter. Usually this is BUSS voltage, and is quite normal. The size of the wires alone to the meter prevent it from "coming back up". again ... normal.

The fact that revving the engine does not bring it up just means the voltage regulator is working correctly, and also confirms paragraph above.

BT3

Reply to
BT3

Reply to
pond jumper via CarKB.com

in regard to issue of voltage drop of blower motor this is normal the blower draw alot of current from battery and alt has to keep up. One thing I have seen no one offer is to check the vacuum lines if vacuum pressure not right this will give you stalling problems. I would recheck those grds on all places might be just a bad bat cable or loose grd you can't see. Any way just my two cent worth

Reply to
shadetree mx

Hello again, People !

Well, after two weeks, I am no further ahead !

Truck runs better with the new oxygen sensor disconnected and even then it still has those major voltage drops where the headlights, blower motor, dash lights all go very dim or slow ......but it runs withour dying out ...most of the time.

If I re connect the o2 sensor, the truck runs like crap from the moment it is started. The engine runs poorly, voltage fluxuates ..blah ..blah...blah ....same old story.

I am totally baffled as to how the truck runs better with the new o2 sensor disconnected ???? I am totally baffled as to how or why it turns completely to crap once the NEW o2 sensor is re connected.

( I've tried two aftermarkets and a gm 02 sensor ...all with the same results.)

The vehicle keeps coding for an o2 sensor ....even with the three new ones I tried.

I am now beginning to think I may have a screwed computer in the vehicle. Is there a way to test these computers ???? The mechanic who is working on my vehicle says he knows of no way to test it other than swaping it out for another one? I find that hard to believe !!!!

Anyone got any advice to offer on computer testing and the like ???? How would I test the computer to verify that it is working properly ??? What info would I require if I went hunting for a used unit ???

I am about three days short of throwing in a lit MATCH !!!!!!!!!!

Reply to
Dairmada

OH ........the voltage drop I experience .......it is not a normal thing .....not at all ! Actually, it's a severe fluxuation where the voltage hand drops from 14v down to 9 v ......then a second later it bounced back up to 14. That's the way it behaves ...up and down like a yo yo .......then, while it is happening, if I floor the accelerator, everything returns to normal for sometimes 5 minutes and sometimes 30 minutes ...but it always returns. When it comes back, I just floor it again for a second or two and all is normal again for another time interval !!!!! This happens when the third new o2 sensor is connected and also when it is disconnected. The only improvement I notice is that with the 02 sensor disconnected, the thing idles and runs better than it does with the 02 sensor connected. However, either way, that voltage fluxuation is present no matter if the o2 sensor is connected or disconnected.

Reply to
Dairmada

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