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 !