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1996 GMC Pickup Won't Start
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djdavis75
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Oct 14, 2008, 9:14 PM
Post #1 of 18
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1996 GMC Pickup Won't Start
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I have a 1996 GMC full size 2WD regular cab short bed pickup truck with a 4.3L V6 engine. The pickup has about 150,000 miles on it. The pickup won't start most of the time, and if it ever does it runs very rough, even at higher RPMs, and usually will only run a short time before it dies and then usually won't restart.
This problem started today after driving the pickup about 15 miles. I noticed while doing 65mph down the highway the pickup seemed to cut out slightly but then continued to run fine. I pressed on the accelerator hard and it accelerated normally. A few more miles down the road it did the same thing again and then suddenly lost power. I pulled to the side of the road and it was running very roughly. It did start back a few times throughout the day as I worked with it trying to figure out the problem but it would usually die shortly thereafter and ran very roughly. One time it actually started and ran normally, but when I tried to pull onto the highway it lost power, began running rough, and died. Most of the time it won't even attempt to start.
I've had two similar, but not exactly the same, problems with this pickup in the past. Basically won't start and dies while running. The first was traced down to a bad contact in the ignition switch which powered the ignition system. This was repaired several years ago. I also replaced the fuel pump and fuel filter within the last year due to loss of power at higher RPMs and finally for not starting or dieing while running.
Here is what I've done so far to troubleshoot the problem. I changed the fuel filter and verified the fuel pump is running when the key is turned on and while cranking the vehicle. The fuel pump sounds normal, unlike when I had the failing fuel pump earlier in the year, the sound was abnormal (slow sounding) then. I bought a fuel pressure gauge and checked the pressure at the port on the fuel line on top of the engine. The pressure was 55psi, then jumped to around 65psi when the pump was running. I don't know if I actually checked it while cranking the engine or not. I don't know what the correct fuel pressure should be.
We also pulled one of the spark plug wires loose and verified it will arc to the metal of the exhaust manifold. So the engine appears to be firing, at least some of the time. I also verified there was power at the ignition coil with a test light. I also checked the fuse box under the hood and made sure everything labeled ECM or IGN was getting power when the key was turned on. This wasn't happening when the ignition switch failed several years ago, but everything seems to be getting power now, at least at that point.
We tried squirting some starting fluid into the engine and it would not run or attempt to run. We also tried pooring a small amount of gas in and it also would not run or attempt to run.
The pickup was very low on gas this morning when I left, so I stopped about 3 miles from my home and added 3 gallons of gas. I intended to add more once I got about 25 miles from the house where prices are much cheaper, but I never made it that far. I thought maybe I had some bad fuel, so I added an additional 5 or 6 gallons to the tank from another location. There are probably now close to 10 gallons of fuel in the tank. This hasn't seemed to help and I've heard no reports from other people of bad gas from the local station.
This is probably an unrelated issues but I thought I'd mention it just in case. The vaccum booster on my brake master cylinder has had a vaccum leak for the past several weeks that has been getting progressively worse. It only leaked when the pedal was pressed and you could hear it from inside the cab of the pickup. It also didn't leak if you held the brake hard to the floor. I've just been living with it this way until I had a chance to change it. I did pulled the vaccum line loose from the master cylinder today and plug it off just to make sure it wasn't the problem. It didn't seem to make any difference.
My dad spent some time with me today helping me troubleshoot. Based on what he saw he said it's almost like the ignition timing isn't right or something. We do have a timing light if there is anyway to check the timing on a computer controlled vehicle like this.
Anyway, I would greatly appreaciate any help anyone could give me on this. I spent 8 hours on the side of the road working on it today and I'm just out of ideas at this point.
Thanks,
David
(This post was edited by djdavis75 on Oct 14, 2008, 9:21 PM)
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djdavis75
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Oct 15, 2008, 5:25 PM
Post #2 of 18
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Re: 1996 GMC Pickup Won't Start
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We purchased an Actron CP9185 scan tool. It displays a code of P0300 Random/Multiple Cylinder Misfire Detected. I haven't gotten any replies yet, so I thought this extra information might help.
Thanks,
David
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Tom Greenleaf
Ultimate Carjunky
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Oct 15, 2008, 8:00 PM
Post #3 of 18
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Re: 1996 GMC Pickup Won't Start
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Have you looked at the cap and rotor yet?
T
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Jeff Norfolk
Enthusiast
Oct 15, 2008, 8:23 PM
Post #4 of 18
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Re: 1996 GMC Pickup Won't Start
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I think Tom is on the right track. I have seen this style rotor under the cap break. There are 2 hold down screws on the rotor and they will some times break right there where they are held on. This will cause an intermittent run bad or no start. Reason being is that the rotor will still turn and fire just not strong or at the right time. It can give the appearance of having spark just weak spark or misfired spark. Pull the cap and take a look. If it won't run when you pour gas down in it then it is either a spark problem or conpression problem. Likely the spark is the issue though. Good Luck
Jeff
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djdavis75
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Oct 16, 2008, 11:19 AM
Post #5 of 18
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Re: 1996 GMC Pickup Won't Start
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I pulled the cap and rotor off and I didn't see any problems with either of them. I took my ohm meter and checked to make sure none of the posts in the cap were shorted together and they weren't. I didn't see any cracks on the rotor or cap. I replaced the cap and rotor within the last year when I was trying to track down a problem which turned out to be the fuel pump.
Thanks,
David
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Tom Greenleaf
Ultimate Carjunky
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Oct 16, 2008, 11:53 AM
Post #6 of 18
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Re: 1996 GMC Pickup Won't Start
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Just a thought: GM V6 @ 150k may have a loose timing chain. You can get an idea with an intermittent problem unseen by this by watching dist rotor turn while watching crankshaft while turning by hand (socket on bolt) back and forth on any marked "degree" indicator on it to see how far back and forth the crank will turn before the rotor will turn. More than 5 degrees starts to worry me if you can nail it down that way,
T
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Rlmtex
Novice
Oct 16, 2008, 3:19 PM
Post #7 of 18
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Re: 1996 GMC Pickup Won't Start
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You might want to check your compression. A compression gauge is relatively inexpensive I got mine at Harbor Freight for $10. You should read somewhere around 150#. If your compression is low that will give you something to go on. If the mechanical timing is off enough to prevent starting your compression should also be low.
Does GM still use the ignition module inside the distributor?
Also from past experience I've had dist caps fail in less than a year. Drove me nuts because I knew I had a relatively new cap on it.
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Jeff Norfolk
Enthusiast
Oct 16, 2008, 3:36 PM
Post #8 of 18
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Re: 1996 GMC Pickup Won't Start
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Just to add to earlier post. I had a #350 model same year in shop today. Same symptoms as yours. Would not run with starter fluid and had spark and compression. No starts though. Fuel pressure was fine. Turns out that the coil was weak. Still firing but when I put a spark checker on instead of grounding the wire it showed a very dim bulb. Changed coil and problem solved.
Jeff
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djdavis75
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Oct 17, 2008, 9:52 AM
Post #9 of 18
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Re: 1996 GMC Pickup Won't Start
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Thanks for the suggestions. I think you guys put me on the right track. I removed the cap and rotor as stated and then put everything back after I didn't see any problems. But after I got the battery charged up and tried to start it I heard a clicking under the hood. I had someone else crank it while I looked and there was a bunch or electrical arcing in the area of the distributor. I pulled everything apart again today and it seemed I had everything together right the first time. Anyway, after I put everything back together for the second time it fired right up and ran fine. Scan tool showed no error codes or anything.
So is it possible I have a hairline crack in the cap or in the insulation on the coil wire or one of the plug wires that is shorting out the coil sometimes? I noticed a few times it did start, on the day it broke down, was after we had been messing around under the hood and touching/pushing around on things.
Anyway it runs fine now, but I know the root problem isn't fixed. Do you think a new cap and set of wires are in order? The cap is less than a year old but the wires are real old.
Thanks,
David
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Tom Greenleaf
Ultimate Carjunky
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Oct 17, 2008, 1:24 PM
Post #10 of 18
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Re: 1996 GMC Pickup Won't Start
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YES! The high voltage carrying anythings can be the troubles. If all is well and dandy for the moment let it run a while to clear itself up - plugs etc may have been stressed, fouled a bit from the attempts. Then go back when it's only cool to warm on engine and spray water (don't laugh - I use Windex) spot by spot which should surface the part(s) that leak if unseen and that may kill it again so try to know just what you sprayed that killed it vs wet the whole area and not know what part(s) are at fault. Good parts won't object to moisture but shocking HOT parts with water/windex isn't so good either.
The flaws can be near impossible to see. Some are just like a light pencil trace and actually called carbon tracing.
I really think you've found the fault. You seem to be having a better week than I am with stuff!
T
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djdavis75
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Oct 18, 2008, 10:13 AM
Post #11 of 18
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Re: 1996 GMC Pickup Won't Start
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Well I replaced the rotor, cap, and all the wires and that seemed to stop any arcing. But now it will start and run a few seconds then start missing. Sometimes it will die and blow back through the intake. Still think I've got some sort of ignition problem. Not sure where to go from here though.
Thanks to everyone for your help so far, any additional help would be greatly appreciated.
Thanks,
David
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Tom Greenleaf
Ultimate Carjunky
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Oct 18, 2008, 10:56 AM
Post #12 of 18
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Re: 1996 GMC Pickup Won't Start
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Ok: Just Googled a bit and found there's four possible ign set ups for this engine for that year which didn't help. If dist has a pick up coil, coil, and module inside it could be related to those and that type should have a holdown to lock timing which should be checked.
I still wonder if the timing chain is involved - especially now with this blow back thru intake. I know that seems impossible that it could be jumping and still jump back to the right spot and not just quit but I've seen that several times over the decades now (cough ) and as said earlier can be guessed well by watching the rotor move when crankshaft is turned back and forth with a socket on bolt to damper.
OE chains fequently come with a nylon gear that with the best of care still doesn't like higher miles and time - nice call car companies!
You might also have luck blowing air inside dist under cap with compressed air (careful) to get any accumulated dirt out of any pick up coil stuff in there.
Also can get a good idea on valve timing (t-chain controlled) with a vacuum gauge put close to actual intake manifold vacuum source as you can,
T
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djdavis75
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Oct 18, 2008, 1:12 PM
Post #13 of 18
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Re: 1996 GMC Pickup Won't Start
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I know you're probably getting tired of me. :) I took what I thought might be an ignition module off, it's mounted on a bracket with the ignition coil, got mad, put it all back together, and it's running fine now. I really don't understand this thing.
Anyway, this pickup does have a distributor but it's not like the older GM ones with the coil in the cap and the module in the bottom. The coil is on a bracket above the intake/valve cover area. Like I said, there is a black thing with a heat sink mounted on the same bracket with the coil. I wonder if this is some type of ignition module or all or that's taken care of by the main computer now.
I don't know about the timing being out, I thought that might be a possibility but then sometimes it just runs perfectly fine.
What other sensors/electronics could be screwing up to cause it not to fire or fire out of time? Do you know if these things have an ignition module?
Thanks,
David
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Tom Greenleaf
Ultimate Carjunky
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Oct 18, 2008, 1:54 PM
Post #14 of 18
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Re: 1996 GMC Pickup Won't Start
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That's a GM V8's timing chain shown there should be very similar to your 4.3 V6. Note the slop in the top left in the pic. That larger gear turns the camshaft which turns the distributor. These can jump a tooth or two hence changing the "valve" timing which can make it "POP" back thru intake and then thru some form of magic jump back to the right tooth and be fine for a while. I've seen a few do that and who knows why they didn't just jump the extra tooth the wrong way and engine quit for good till fixed but they did??
You can't see this thing but you can turn the bottom gear by turning the bolt in crankshaft with a socket and watch the distributor's rotor turn. Go one way then the other and you get a good idea of how much slop it has. My guess is 5 degrees seen on the timing marks would be about enough to be concerned. It was just a possibility tossed in as this has 150,000 miles as you said. I would change these out antime a waterpump (this is behind the water pump) failed after 100k just for good measure if you wanted the next 100k trouble free from this type of chain. Chev "V" blocks seem to do very well with high miles but it's still a possibility.
If it's running fine now you probably won't find much wrong with anything electrical now but this would still show slop with the test or if caught when running lousy would show low compression on all cylinders or low manifold vacuum if still running and may or may not POP back thru air/fuel intake when off.
There's a nylon toothed original one showing missing teeth. That one is real bad but I've seen these in this shape come out of good running engines!
T
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djdavis75
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Oct 18, 2008, 8:02 PM
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Re: 1996 GMC Pickup Won't Start
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I think one thing that is making this so hard to pin down may be that there are several things going on. My dad said something about clicking like arcing the day it broke down. Then I noticed arcing the other night, but after removing the cap and putting it back it stopped and the pickup ran. Then I replaced the rotor, cap, and wires and it started messing up again. But now there is no indication of arcing. Don't see it and don't hear it.
The problem I'm having since fixing the arcing seems to be a little different than before. Before it wouldn't start most of the time, and if it did it immediately ran poorly and usually died. Now it will start fine and run for 3 to 5 seconds fine every time. Then sometimes after about 3-5 seconds it will start cutting out and usually die. Other times it will start fine and run fine and you can drive it around without any problems.
I had someone suggest it might a problem in the fuel system. I hooked the fuel pressure gauge back up today and it showed 65psi when the pump came on, but dropped back to around 58 psi when the pump went off. Once started the fuel pressure ran around 55psi. It would always start and run fine a few seconds then start cutting out and die. I took the fuel pressure meter off and set the air intake back in place and screwed it down. After that it started and ran fine again. I've been told the minimum fuel pressure should be 60 psi while running and I don't seem to be getting to that level.
Anyway, just thought I'd throw this in there to see if that gave anyone any ideas.
Thanks,
David
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Jeff Norfolk
Enthusiast
Oct 18, 2008, 8:09 PM
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Re: 1996 GMC Pickup Won't Start
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No 50-62 in the required spec. it will run on less just not very well. Sound like an ignition problem. have you tried a new coil yet. Even though you have spark it may be weak, sometime weaker than others. Hence the on again off again problem you are having.
Jeff
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Jeff Norfolk
Enthusiast
Oct 18, 2008, 8:12 PM
Post #17 of 18
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Re: 1996 GMC Pickup Won't Start
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Also just a thought. recheck your wire routing. if it is now backfiring after plugs and wires you may have a couple crossed. it happens to the best of us
Jeff
(This post was edited by 10-5-6-6 on Oct 18, 2008, 8:14 PM)
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djdavis75
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Oct 19, 2008, 12:45 PM
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Re: 1996 GMC Pickup Won't Start
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I think the ignition shorting out was the problem and you guys pointed me in the right direction on that.
I guess I've officially earned myself the title of Chief Idiot. I figured out what was causing the current problem I've been having. Every time I've had the problem where it starts fine and runs a few seconds but starts cutting out I've had the air intake (I guess that's what you call it) off. I didn't realize it wouldn't run right with that off. I pulled it off on my dad's 1997 Chevy truck with a 5.7L V8 and it won't run right either with it removed. I also checked the fuel pressure on his truck and it's identical to my truck.
So I think I had fixed the problem with the cap, rotor, and wires but thought I hadn't because I often tested it with the air intake disconnected. Which resulted in it not running right. So now I know. :)
Sorry for the confusion and many many thanks to everyone for helping me out.
David
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