Mechanics

SENSORS

1999 GMC Truck

Electrical problem
1999 GMC Truck V12 Two Wheel Drive Automatic 138000 miles

This new body style half ton truck is used as my work truck. Over the past few years I have been having quite a bit of trouble with sensors. It is getting worse here lately. About a year ago I replaced a sensor (that my code reader said was defective) PO 141 and it went out again about 6 mos. After. Within the past 2 months I have had to replace it again along with a camshaft position sensor.I went ahead and replaced the entire catalytic system also. Then I got a reading that said the throttle positon sensor was bad too. Replaced that one. Now, within the past 2 weeks my truck kinda runs away at idle and my code reader says the following: PO 141 pd 4/04, PO141 02/04, PO 121 1/04. And Ive gotten misfires on PO 304 03/04?
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Dallas Ford
November 27, 2008.



Ok first get some mass air flow cleaner and clean the mass air flow unit. Clear all the codes and see what comes back. If all the codes come back it may be a bad PCM and if you have a digital multi meter then we will test to see ok.

Racefan966
Nov 28, 2008.
I am not familiar with " mass air flow" cleaners.I put a new air filter in about 3000 miles ago. And checked it last Sunday. Found that the installer had not closed the airfilter Hatch door completely. Fixed that and then cleared the codes previously mentioned. Drove it till today (Friday). Following codes returned. PO 141 pd 04/04. PO 141 01/04. PO 304 02/04. PO 108 pd 03/04. Should I do the cleaner (please suggest here) and start over?Thanks. Dallas Ford

Tiny
Dallas Ford
Dec 5, 2008.
Ok first which engine does your Silverado have? Is it a 5.3 or what? Chevy does not have a V12. As for the codes they are problems that could be caused by a dirty mass air flow sensor sense the air cleaner box was not fully shut this is where I would start and clear the codes again and go from there. So go to you local parts store and get a spray can of Mass Air Flow cleaner and clean the inside of it by spraying it down with the cleaner and do not get any other kind of cleaner it has to be mass air flow cleaner ok. Here is a pic of the mass air flow unit all you need to do it undo the band clamps and electrical connector and take it out and clean the inside of it then put it back and clear the codes and lets see which ones come back so we deal with the actual problem ones ok. Get back to me with the codes that return and we go through them one at a time.


http://www.2carpros.com/forum/automotive_pictures/249564_396994_1.jpg


Racefan966
Dec 5, 2008.
It is a V6, standard shift, regular cab, new body style, Sierra.I will go get the cleaner and perform your suggestions. Then get back. Thanks mucho.D. Ford

Tiny
Dallas Ford
Dec 5, 2008.
No problem let me what turns up an if any codes come back let me know what they are and we will go through them. Thanks.

Racefan966
Dec 6, 2008.
OK.I found the mass air flow cleaner and did a pretty good job of cleaning the sensor. Last Monday. This is Friday. No codes as of yet. However, when its cold it starts fast. After warmup it starts what I call mushy and then will rev up to between 1500 and 2000 rpms and hold until I cut it off. Sometimes does not do this.I have gotten at least 1 backfire each of these past 5 days during the day when I start up after driving for maybe 5-10 miles at about 50 mph.I checked for a code on the backfire and its not showing one. How am I doing so far. Thanks for your time and thoughts.D. Ford

Tiny
Dallas Ford
Dec 12, 2008.
I forgot to reply to your question. About the engine. Sorry. It is a V6.A little standard shift, new body style, Sierra, reg. Cab.I use it as my ranch truck.D. Ford

Tiny
Dallas Ford
Dec 12, 2008.
Ok so far so good there are not codes so that is good but now on the backfire where is it coming from? Is it backfiring through the intake or out of the exhaust? Get back to me on that and we will see where we need to go on that. I do have another question for you when was the last time you replaced the spark plugs and have you checked the cap and rotor lately as this has a horizontal cap they have problems corroding so if you would check that and see what it looks like. Talk to you later have a great day.

Racefan966
Dec 12, 2008.
I will check the plugs and cap and rotor.I believe the backfire code said it was #4 cylinder? And I believe I hear it coming from under the hood and not out back behind me. By the way, after my last message to you the check engine light came on and before I could drive about 6 miles to the house to get the code reader It went off. And has stayed off 2 days later. It still on occassion wants to rev. Up and not idle down until I cut it off. Then the next start up may be fine. Going to go back to work on it and thanks some more for continued help.D. Ford

Tiny
Dallas Ford
Dec 14, 2008.
Well.I spoke too soon. Today. Monday morning, the check engine light came on and my code reader gave the following: PO 141, PO 141pd and PO 304 02/03.I did not erase and am going to change plugs, cap and rotor and probably wires before erasing these messages. OK.I have to go to another city to obtain parts first. Thanks.D. Ford

Tiny
Dallas Ford
Dec 15, 2008.
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