1999 GMC Truck Sensors

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.

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

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.

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

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.

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

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

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.

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

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

Ok after the tune up clear codes again and lets see which come back. As for the p0304 and so on that is cylinder missfires on those cylinders so the 02,03,04 are cylinder 2, 3, 4. As for the p0141 we will look into that once we get the missfire taken care of. So let me know how the tune up goes and we will continue from there. You are welcome for the support and thank you for your support. Till later

OK..got new plugs, cap, rotor and new best grade wires....had my local tractor guy put it all on and in...the old cap and plugs were shot to say the least...I went to clear the codes and found a new one since I last messaged...a PO 108....cleared all and will watch and wait....still does not start up like it use to..a little slow......however has some more pep than previously.....By the way another friend of mine who works for a major welding firm in another town says they have a young mechanic that has a super duper diagnostic unit that would probably hook it on if I want to take it over there.......will stand by for now....Thanks...D. F.

Okee Dokee guys.....Saturday I completed the tune up and today (Monday) the check engine light came on.....Codes, 304 01/02 and 141 02/02.....I know this saga is got to be getting tiresome for you and Im sorry....what cha think now....???...D. Ford