Question about 1995 GMC Sierra

4 Answers

I have a 1995 gmc with a 305, when driving down the road and holding at a set speed it begins to kick and fart, but if i excellerate it is fine.Injectors are new, cap is new, fuel pump is new,new plugs, new wires,new egr valve,new air fuel sensor,new injector housing gasket and new tempature sending unit. When humidity gets higher, runs much better or when outside temps are above 45 in runs better.

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  • 15 more comments 
  • mike clark Mar 21, 2011

    John thanks for your speedy reply!! The only thing that makes we thing its not mechanical is the weather . Why does it run fine or almost fine when there is more moisture in the air or warmer outside.When its cold, 20s and 30s and no humiidity it runs horrible. I can say the weather has somehthing to do with it as I have been fighting this issue for over year.So I am fairly certain it has to be some sort of sensor.Do u agree or what are your thoughts? This truck has 73,000 miles on it, i also replaced the computer and coil.All these things I have done have been done over the last few years, but all within 5000 miles.As u can tell, I dont put many miles on it.

  • mike clark Mar 21, 2011

    I havent replaced the ignition module yet, could that be the cause? From my past experience, when those go bad, they just go bad dont they or could that be the cause?
    As u stated mass air flow issues, i did spray carb cleamner along intake gasket to see if there was any leaking.The distributor i believe i replaced about 5 years ago, i think. My memory is failing me as i have replaced so much on the truck im losing track.But I have never replaced the module.
    If i pull the distributor, will these cracks be obvious to the naked eye or is there something that will stick out like a sore thumb other then the cracks? Where is the map sensor located on this truck? Also i did replace the O-2 sensor , only one as that alls that on the truck, which is found is weird.

  • mike clark Mar 21, 2011

    Um, the coil is directly behind the injectors mounted on the intake or right in front of the distributor at the rear of the intake.On the passenger side valve cover is the EGR silinoid and something else right behind it closest to the fire wall ,could that be the mapping sensor?Ok, i will be checking the coil pick up inside the distributor tonight, thanks i will let ya know what i find.This has been a real headache and as u can tell i have talked with several people and we cant seem to figure it out, i bet its going to be soeemthing stupid and obvious. lol

  • mike clark Mar 22, 2011

    I purchased as distributor that came with ignition module and coil pick-up.Along with that i picked up a cap and rotor so that complete ignition piece will be brand new.Hopefully problem solved, will do tonight and let ya know how it came out.Just so ya know, other mechanics I have talked to are interested in your solution as this could be a learning experience for all of us based on your solution.

  • mike clark Mar 23, 2011

    I installed the distributor last night, unfortunately my frickin timing light is broke, so tonight i will set the timing and see how it works.But prelium, it sounds better and seems to run better.I think once i set the timing it will 100%, i will let ya know tomorrow.

  • mike clark Mar 24, 2011

    John, I changed distributor and set the timing,still runs bad. I then installed a new map sensor, no luck again. Again, when i am driving and try and hold the throttle at a set speed it seems like either it is loosing spark or gas and im leaning more towards spark as it seems like all cylinders arent firing at that time when holding it at a set speed.Or firing off and on as thats how it sounds.Can a coil work like that, when its under a load it gives out enough spark and when there is no load it doesnt send enough out? I replaced this about 5-7 years ago or about 7000 miles ago, I wouldnt think so, but is it possible? If the fuel filter was clogged, wouldnt it always run like **** and not only when im holding at a set speed,which I replaced 2 years ago or about 2000 miles ago.Would the EGR silinoid have any influence on when or if spark should or shouldnt be sent, i think not, but just asking as i am so baffled.Or what about the TPS sensor, would that have anything to do with spark or how much gas gets distributed to the engine?I replaced the fuel pump about 4 years ago or 4000 miles ago, so im assuming its good too.AS U CAN TELL, BAFFLED.lol Let me know your thoughts.

  • mike clark Mar 25, 2011

    U think the lobs would be worn with only 71,000 miles on it, seems highly doubtful,only based on the low miles.Plus when the outside tempature goes and stays above the 50 degree range and humiity goes higher, almost all the missing goes aways.Almost like the moisture in the air is getting on the electrical doing something funky to it or a seal swells and the problem goes and stays away.Im so dumb founded on this, only because the outside tempature has somehting to do with it. If i had a worn lob, this wouldnt be happening only in cold temps, it would be a consistant problem and its not consistant,other when its cols outside.How can i check the cam for being worn without removing if u think thats it.

  • mike clark Mar 28, 2011

    To whom it may concern, i have 1995 gmc with a 305, it has 70,000 miles on taken care of very well,garage kept.At the moment it has a miss, very strange when it occurs.I will be driving down the road and in any gear,its a 5 speed,if i am maintaining a speed it begins to miss until i begin to accelerate or de accelerate.Here is the strange thing, when its warm OUTSIDE, above 50 degrees and humid it rarely misses.It only seems to run this way when its cold and low humidity.It still has a minor miss when it warms up, but hardly noticed.Over the period of 3-5 year and less then 7000 miles i have replaced the following,distributor,ignition module, pickup coil,fuel pump,plugs, wires, map sensor,computer,O-2 sensor, removed and did not replace cadiliac convertor,fuel/air sensor,both injectors, gasket between injector housing and intake and egr valve.So as u can tell I have replaced alot and have not been able to figure it out.There are no codes as i have scanned the sysytem several times.I look forward to your answer or reccomendation what the issue could be.Very strange!!!!

  • mike clark Mar 28, 2011

    I would agree it is running rich as u can smell it, but i assumed it was caused by the misfire and the computer was adjusting to off set the mis fire. How do i fix that which sounds like that may fix my problem,hopefully?

  • mike clark Mar 28, 2011

    There is no air intake sensor on the air cleaner or the box.But I did replace the temp sending unit on the intake about 2 months ago.The other temp sensor is for the dummy gage.I will drive this evening with the scanner hooked up watching to see if the temp goes over 180 degrees.I hope this is the issue, didnt think that would be the issue.New thought!! But will it only miss like it does when im trying to maintain a speed, not accelarate or de-accelerate?I am impressed how u knew it was running rich which i didnt tell u.I will give u feed back tomorrow on where the temp is.

  • mike clark Mar 29, 2011

    I hooked up the scanner and did show the engine only going to 181 degree, so i did replace it with a 195,which was in there already,maybe sticking who knows right. I hooked the scanner back up and it still showed it at 181 degrees.Now u say replace the temp sending unit, i did that 2 months ago,so u think its bad again? The truck still runs rough like it did before.Here are some numbers off the scanner when the truck is idleing TPS-.54, KNOCK-2, MAP PA-30, MAP V 100-118, FUEL TRIM- 128, 02MV 235-700 and COOLANT was 180 degrees.Do those numbers help u at all? It stated it was running lean and back to rich, which is normal as the computer adjust. So any new thoughts?

  • mike clark Mar 29, 2011

    I purchased a EGR valve silinoid and am going to replace it tonight.The only code it is showing is #42,which is electronic spark code, which could be anything.I also ordered a TPS sensor that will be in tomorrow.

  • mike clark Mar 30, 2011

    I replaced the EGR valve silinoid and truck is running good. Miss

  • mike clark Mar 30, 2011

    I replaced EGR valve silinoid and truck runs great.

  • mike clark Mar 30, 2011

    I replaced the thermostat and it still reads 180 on the scanner. But i did discover the problem why the truck was running bad, i replaced the EGR silinoid and it runs great. In regards to the theromstat, after i changed it, the scanner still showed it running at 180 degrees, plus the raditior cap is cold, i can hang onto the upper raditor hose and i didnt see any water flow in the radiator, so i think that may be another problem. Thanks

  • mike clark Mar 30, 2011

    His answer didnt exactly fix the problem, but Dave definately got me in the area to do sUm einvestigating which ultimately I was able to fix the issue.I replaced the EGR valve silinoid and truck runs great now.

  • mike clark Mar 30, 2011

    Problem is fixed, i replaced the EGR silinoid and truck runs like a top now.

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4 Answers

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  • Master
  • 1,050 Answers

I would try removing and plugging the vacuum line that goes to the EGR valve. If this solves your problem, you may have an EGR valve that was calibrated for a different vehicle and is adding too much exhaust during cruise. This problem can also be caused by a MAF sensor that is not "seeing" all the air that is entering the engine and causing it to run lean at cruise. Tough to say which one. If it were me, I'd try and find a loaner MAF sensor to try...maybe an auto wrecker? Either way, make sure your ignition timing is correct and the plugs are gapped properly. Low timing and a worn timing chain can also cause this problem. I suspect that this truck has high miles?

Posted on Mar 28, 2011

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  • GMC Master
  • 76,846 Answers

Have you run a test on the ECM (Electronic Control Module) to see if any electronic engine control fault codes are present for the engine or emission control system? This sounds very much like an EGR (Exhaust Gas Recirculation) valve problem or a TPS (Throttle Position Sensor) problem. Do the test first and see what shows up. You can do the test by watching the Check Engine light blink during the test. Go to the link below for instructions on how to run the test.

http://www.extreme-check-engine-light-codes.com/GM%20OBD1%20Decoder.htm

Posted on Mar 29, 2011

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  • yadayada
    yadayada Mar 29, 2011

    Perhaps the MAP sensor is defective, this is really in need a of a professional taking a look see, all I can do is offer advice based on my 40 years of experience as a mechanic. But you are getting ahead of yourself, please do all tests I've mentioned. Without the air of being hooked up to a dealer diagnostic machine to look at the system and what all the electronics are doing this is just an educated guess.

  • yadayada
    yadayada Mar 30, 2011

    Let me know if the other experts advice fixes the problem, I have a real suspesion it will not cure the problem.

  • yadayada
    yadayada Mar 30, 2011

    I said the EGR was suspect right off, did you even read my solution?? I was robbed of this one. Glad it is fixed, all is well that ends well.

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  • Master
  • 829 Answers

I would look at coolant temperature reading on the scanner.I think you are running a little rich and this could be caused by a low temp reading.Also look at intake air temp it should be a few decrees hotter than ambient temp.Good luck! Let me know if I can help.

Posted on Mar 28, 2011

  • Donald Britton
    Donald Britton Mar 28, 2011

    With a scan tool look at engine coolant temp,it should be 195 degrees give or take 3 dgrees.If it itwill not get above 180 then I would replace the thermostat first.Make sure you go back with a 195 degree thermostat.If that does not fix the problem replace the sensor.It will be located near the thermostat housing.If equiped with an air intake sensor then air temp should be a little warmer that the outside air.This sensor will be located in either the airfilter box or the tube going to throttle body.Let me know if I can help further.

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  • Master
  • 1,702 Answers

This is tuff, my first thought is the engine is missing, but you have replaced almost everything, but i do have a couple of ideas, the 305 had allot of problems with camshafts the lobes get worn down and do not allow enough lift for the valves, witch can cause a miss fire, when you gouge the throttle it seems to go away just because all the other cylinders pick up there output, about the only way to check this is with a compression test or remove the intake and look at the lifters to see if they are cupped out.

the 2nd thing is to check the coil output, it could be the ignition coil is getting weak, you can check the output with a spark tester, if you don't have one you can make one with an old spark plug, just take an old plug and brake the ground leg off of it then install it in a spark plug wire and hold the threaded part against a good ground and crank the engine the spark should jump from the center of the plug to the out side case and should be very bright if not replace the coil.

also the 305 V8 had allot of problems with the distributor shaft, it was even recalled many times for this problem, the magnets in the shaft that send a signal to the pick assembly in the distributor get cracks in them that cause all manner of running problems.

out of the 3 this was one we have seen the most, it is so common that most parts stores keep the distributor in stock.

i hope this helps, please keep me informed, and let me know if there is any thing else i can do foe you.

Posted on Mar 21, 2011

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  • john nail
    john nail Mar 21, 2011

    i did see were you stated that is seemed to be better when it was warmer, that could still be any of the problems i talked about, when the engine is cold it requires more output to mantain rpm the warmer the intake air the less effert is needed to matain rpm, and i was just hoping that the wet air was a fluk, but mabey not, the only sensor i can think about that might cause this is a mass air flow or a map sensor, but i am still leaning on the distiributor just because we have seen many of these fail over the years and it could defantly be efeceted by humety and temp.

  • john nail
    john nail Mar 21, 2011

    like you i dought it is the module but you never know, a more proble cause would be the pick up coil inside the distributor, take a close look a the wires going from the pick up coil to the module we see them lose there coating and start grounding out to the base of the distrbutor the map sensor is on top of the engine on the passanger side valve cover most likely mounted to the coil bracket. the cracks can only be seen with a lab scope.my best recomendation is if you supect the pick up coil replace the distrubutor.

  • john nail
    john nail Mar 21, 2011

    the other thing on the valve cover is the map sensor there will be a 3 wire plug in a vaccum hose on it.....good luck....i think the distributor will fix it

  • john nail
    john nail Mar 22, 2011

    think potosive, good luck make sure you get it back in time and most of all HAVE FUN!!

  • john nail
    john nail Mar 25, 2011

    OK..coils can do strang things, but you can test the output, take a old spark plug and remove the ground leg and then install it in a plug wire and ground the threads and start the engine the spark should jump from the center to the threded caller, the fuel filter would show up more under heavy load, the TPS can also be tested .5 to .75 volts at idle over 4.5 volts at wide open and a smooth transion from .5 to 4.5 with no drops, EGR should not effect the engine at speed if it working it should be open at speed if it were stuck it would effect idle not hiway speed. i still think you need to check the camshaft and make sure you dont have worn lobs, i think the problem is mechancal not electrical, if you think it is the fuel pump check the pressure, that would be the best way to check it 13 to 17 psi.

  • john nail
    john nail Mar 25, 2011

    you will have to remove the intake manafold, to look at the camshaft, fuel mixtures are differant at differat temp's could be that because the mixture is richer at cooler temp. that the valve travel is good enough, b ut this is just an idea, the miles are low but on the 305 with the bad cames we seen them go bad at allot lower milage some as low as 30,xxx miles my bigest concern is the popping or ******* as you say this sounds mechancal.

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