96 Chev K1500 350 Vortec Will Not Start and Backfires

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#1
96 Chev K1500 350 Vortec 160K Miles No Aftermarket Stuff Auto Tranny​

The truck will crank over but wants to backfire and tries to kick back and stalls the starter out. I towed it to a friends house that is a ex chev mechanic and he said that it was the fuel pump. I know that these rigs are notorious for going through fuel pumps. I had already replaced this pump myself about 6 years ago. I bought the pump from Schucks and they had a lifetime warranty on it. Amazingly they accepted the return and gave me a credit for the amount that I payed for it then. They don't sell that brand anymore so I bought the package deal with new floats and everything for 200. Gave it to my friend and he installed it and the truck ran. Took it home and now it is doing the same thing all over again. My friend is going to come over sometime this week and try and figure out what the problem is.
I was doing some research on TSBs and found one with the exact description that I was having. The number is 000604014. So I called up another friend that lives a long ways away and he gave me the info on it. It said to replace the crankshaft position sensor and then reset the computer. So I went and bought a sensor installed it and forgot to reset the computer before trying to start it. It changed nothing, still the same old problem. So I decided to reset the computer by disconnecting the battery, a good 10 to 15 minutes or so. Hooked it back up and still has the same problem. So I am wandering if anyone has had this same experience? I have also had the problem that other people have talked about where in 3rd gear at 60 mph or so you can just barely feel the motor hesitate or is barely missing. You have recommended to install the new fuel injector kit for this problem, do you think that this could also be tied in with the backfire problem? I forgot that a few months ago I could start the truck just fine by just barely cranking the started and it would always start right up, then it slowly got worse and worse. at the beginning it use to backfire but you could still barely get it started, once it started it ran just fine. Anyways any help would great.
 

Gus

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#2
Did you ever put a fuel pressure gage on this?
 
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#3
by chance did you check for codes as per this part of TSB?

Correction
Inspect for a stored powertrain DTC code P0338. This DTC will NOT illuminate the "Service Engine Soon" light. If this code is stored, the Crankshaft Position Sensor, P/N 10456607, MUST be replaced and the remaining components inspected for damage (engine block at the starter boss, the starter drive housing, and the engine flywheel starter ring gear).
 
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Hi guys I am back look at that it has been a year. Sorry about never following up. The problem went away and I hardly drive it so never worried about it. Well guess what its back. Same exact problem. I took it to a mechanic and he checked it and said that their are no codes on the computer except for one about the EGR valve which I have known about for years, the light only comes on during hard acceleration and towing something. Anyways don't worry about that. He did notice one thing that was odd is the SES light does not come on when you turn the ignition on. All the other lights come on for their normal bulb check except for the SES. Does anyone know what might be the cause of this? My mechanic said he has seen this one other time and said that there were problems with the computer and had to replace the whole thing. This weekend I am going to install the kit from GM for redoing the ground on the computer harness. I have had shifting problems with the transmission lately and am going to try this to see if will solve any of the problems.
The mechanic put his pressure gauge on the fuel line and it read 55 while idling and then when he would give it some throttle it would then go up to about 63. He looked up what should be normal and said that 55 was okay but if it was under then there are problems with the fuel regulator. I am thinking that it is so close to being under 55 that I might also order the GM kit for replacing the injectors which I think also replaces the fuel regulator. I have been reading the other forums with you guys and that seems to be a real common problem. I plan on keeping the truck so I figure that I am going to have to do it sometime down the road anyways. My mechanic said that sounds like the problem, that possibly the injector gets stuck open and sprays too much fuel into the cylinder and then on the compression cycle it has too much fuel and then it can not even bring the piston all the way up to continue the cycle and so that is why it tries to kick back or completely stalls out the starter. Does this theory sound kind of correct?
I hope this is enough info. If not just ask.
Thanks for any help
 

Gus

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#5
D-I-A-G-N-O-S-I-S......OR be a parts changer.....your choice....
 
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Diagnosis sounds good to me. So where do I start? I know for sure that I am going to do the ground kit for the PCM this weekend because the transmission has been slipping and this is a very common problem with this year of truck. This info comes from Transman. It is a cheap fix so it could not hurt. If it fixes anything, if not then at least it could not hurt.
Thanks
So for diagnosis with the motor where do I start?
 
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#7
Chevy Pickup hard starting

96 Chevrolet K1500 Silverado
5. 7 Litre 350 Vortec
Auto Trans
No Aftermarket Stuff
170 K miles
Maintenance done regularly

Recently changed the fuel pump, mass air flow sensor, battery, crankshaft position sensor, spark plugs, distributor cap, spark plug wires.

The problem I having is when I go to start it sometimes tries to backfire and then it will just totally seize the motor so that the starter can not turn it over. Then if you try to start it again it will sometimes just crank over and not start, other times it will do the same as the first time. I had a mechanic check the fuel pressure and when it was idling it was running about 55 psi and then when he would increase the throttle it would go up to about 63 psi. He also checked the PCM and the only code it had was there was EGR problems. He did not give me the code number for it. One thing he thought that was really strange was when you first turn on the ignition and all the dumby lights come on for there bulb check the service engine soon light does not come on. I know that it works because it had come on for the EGR problem a couple of weeks back. If anybody could help me start the diagnoses on the problem that would be great.
Thanks
 
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#8
Re: Chevy Pickup hard starting

two thoughts
1) check ign switch....I think this is a known problem year
2) check TSB's .....a problem with CKP causing an over advanced ign timing

the lock up could also be fuel or coolant causing cylinder lock...any evidence of fuel or coolant in oil?
 

Transman

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#9
Re: Chevy Pickup hard starting

Throttle body or CSFI? Lots of problems with the injectors on these units (CSFI), fairly easy check for this. Remove the air cleaner and look down the throttle with a strong flashlight, if you see liquid sown there then the injectors or regulator are leaking. Replace with the updated injector kit & bracket. Post back, Transman
 
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#10
Sorry it has taken me soo long to reply back. Been really busy. I had been doing some research in the forums before writing in and had seen the problem that transman wrote about. The only problem is that it has warmed up here some and it starts just fine. No kick back problems. The only thing that I still notice is that you can feel a very slight miss while driving down the highway. I remember reading about other people that had this same problem and transman thought that it might be the injectors. You asked me to look down in the throttle and look for gas, do you think that this is will still tell me if there is a problem since it has warmed up and starts just fine? The truck was having problems when it was in the teens and 20's at night and not really getting above freezing during the day. Now our lows are in the 30's and highs in the 50's. Also the local chevy dealer printed out the TSB for the new fuel injector kit to change it from CSFI to MFI. I just did not want to spend the money for the kit ($600) unless I knew for sure that was the problem. Thanks for all the help in diagnosing the problem.
 

Transman

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#11
Yes! Please look for leaking injectors/regulator. This can be an "Explosive" situation under the right conditions. Besides, the replacement will add fuel economy & performance to your vehicle as the injectors will be directly controlled not the lines as what you already have. Transman
 
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#12
When I hear backfiring, can only think about ignition problems, with rich fuel problems and good ignition, shouldn't backfire, but will see black smoke from the exhaust. With erratic ignition, if the spark does come, can come at any time, even the wrong time, and if the intake valve is opened, it will backfire.

With the HEI, problem can be anywhere between the battery and the distributor, even ground, or the HEI itself. Ignition switch is a joke with a tiny dimple on a piece of bare corroded copper that us suppose to make contact with another piece of corroded copper. Kind of like touch two 22 AWG bare copper wires together. And those lovely bare brass Packard Electric spade terminals that also turn green.
 
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#13
I'm going too stick my nose in here and suggest you check the distributor cap. This sounds like a typical cracked distributor cap and is getting wet inside during cool, cold or wet weather. Pull the cap off and check for a crack or tracking marks. Might even have to wait till it starts acting up again and then look at it. Let everyone know what you find. . . . . . . . . . . Roger R.
 

nickb2

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#14
Coil towers like to melt on these trucks too. The coil terminl of the cap I mean. I had one exactly like this one in the other day, A c1500 350 vortec. Cap wasn't bad, bud boy was the rotor shot. Almost was melted through. Would work fine when warm. Amazing enough!! Cold air is dense and spark goes through it harder. Give big ass GM gaps spark plugs and bingo, all secondary spark is crap. Guy came back today with his truck. Busted a brake hose, but he says gas mileage got better since tune-up and injector cleaning. Gas filter was done at tune-up also. Clean up the basic tune-up then diagnosis is good if still missing while driving at 60mph. I mean this is a 96!! Chevys are good but not that good. Gotta maintain right?
 
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#15
Spent 35 bucks for a GM distributor wrench, then they switched that single bolt to metric, that still tees me off. Refuse to pay another 35 bucks. No problem with my P-30 all kinds of room in the back to remove it, had to remove the entire air cleaner on my DeVille, can't even remember how I removed the distributor on a 4.3 L, but on both retapped the hole for an English bolt to make timing a lot easier. But have a lot of fun with these HEI's once on the bench, even like to buff the aluminum. I use an electric engraver to put the gear on back the same way it came off.

Can tell you this, in 1972, Delco had to provide the entire HEI ignition system with the silicone spark plug wires to GM for six bucks, ha, recall checking with a local dealer, was $156.00 just for the base of the distributor, in 1972! Was the easiest system to hot wire, just run a wire from the battery from the BAT terminal and use a remote starter switch to crank it. Also never found one where the initial timing was set properly, worse was the P-30, a full 30* off! What a difference in both fuel economy and performance that makes. And when you first hit the key, it starts. Kind of prefer the older centrifugal advance, can play with the timing curve by compressing or expanding the springs, have to take the microcontrollers word for it, but like to check it's advancing when all plugged back together again.