1997 Chev C2500 5.7 spark only on cyl 1 & 8

[sojatech]

Full throttle onto freeway then engine shut down. Shifted to neutral, couldn't start. Scan shows NO trouble codes set or pending. CKP good pulse, coil giving good spark. Distributor has 0.1 ohms to each contact but only sparks on cylinders 1 and 8, remaining circuits have rare intermittant spark (less than 40KV).

The Ignition Control Module is getting pos, neg, switching signal and IC (Ignition Control), good.

Tested Ignition Coil Switching Signal from ICM. Fuel press 60 psi, compression 210lbs.

When I try to start the crank stops abruptly. Unpluging fuel injector signal allows it to crank fine.

Is there a good way to check if the timing chain has jumped a sprocket? Any ideas what to check next?

 

[Jsdirt]

If the chain jumped the sprocket, you ignition timing should be several degrees off from where it should be - that's usually a good indicator if the vehicle ran perfectly prior to the issue. Set #1 at TDC COMPRESSION, and see which lug on the distributor the rotor is pointing at - it should be slightly past the #1 lug / wire when at 0° TDC compression. If pointing at any other lug, it has more than likely jumped.

 

I had a nightmare of a '96 Tahoe here once that did that same thing - would crank, and stop abruptly, like the valve timing had jumped. My buddy had tore into it prior on a guess that it jumped time. After hacksawing the Y pipe in 3 pieces, and attempting to drop the oil pan (4x4), he gave up and sent it here. Turns out, the computer took a dump. Chain and sprockets were perfect (very new, actually) and timed spot-on. As soon as I got another computer, it fired right up and ran. Still does that stop for a second thing while cranking - I suspect an ignition timing adjustment would probably fix that.

 

That POS still runs on 6 cylinders though. Been through the thing top to bottom. I threw in the towel. I suspect the junkyard sold me a V6 computer, because they flat refused to honor their 90 day warranty, and demanded proof from a dealer that the computer was in fact at fault. Yeah .... I'll run right down to a dealer with the rusted out 200k miles Tahoe and drop a grand on troubleshooting - great idea ... Needless to say, I will NEVER do business with those crooks again ...

[sojatech]

Thanks for your quick reply. I tried swapping out the computer with a spare that has transmission problem, no change. BTW When changing a computer it still needs to be programmed with VIN number, milage and other specifics for your vehicle (shift points, timing, etc) else it won't run or pass a smog test.

Anyway, my mechanic told me to check that the distributor rotor is turning. He is correct! The gear on distributor is bad, the rotor flops around a bit but doesn't turn. I guess thats why he gets the big bucks, estimate $500. I checked on a few sites and replacement distributor is about half that price.

 

[Doug_Scott]

Thanks for your quick reply. I tried swapping out the computer with a spare that has transmission problem, no change. BTW When changing a computer it still needs to be programmed with VIN number, milage and other specifics for your vehicle (shift points, timing, etc) else it won't run or pass a smog test.

Anyway, my mechanic told me to check that the distributor rotor is turning. He is correct! The gear on distributor is bad, the rotor flops around a bit but doesn't turn. I guess thats why he gets the big bucks, estimate $500. I checked on a few sites and replacement distributor is about half that price.

 

 

The gear on the distributor does not normally just wear out. Take a good look at the gear when you get it out and see if there is some pattern to the wear on it. That gear also drives the oil pump, so you may want to check oil pressure when you get the gear replaced. I have only ever seen or heard of a distributor drive gear failing once before, and that was on my own car. Mine failed due to previous owner/engine builder putting a brass drive gear on along with a high pressure/high volume oil pump.

 

Keep in mind that if the gear is either worn or broken, the rest of the gear is in the engine, somewhere.

 

Have you actually pulled the distributor to check the gear? It can still be timing chain/gears, if the engine has one of those fibre gears on it, they are known to shed the teeth and stop turning the camshaft and therefore distributor. That is far more common than distributor drive gear.

[Jsdirt]

Thanks for your quick reply. I tried swapping out the computer with a spare that has transmission problem, no change. BTW When changing a computer it still needs to be programmed with VIN number, milage and other specifics for your vehicle (shift points, timing, etc) else it won't run or pass a smog test.

Anyway, my mechanic told me to check that the distributor rotor is turning. He is correct! The gear on distributor is bad, the rotor flops around a bit but doesn't turn. I guess thats why he gets the big bucks, estimate $500. I checked on a few sites and replacement distributor is about half that price.

 

Yeah I second what Doug said - there's got to be a reason, if indeed the gear IS bad on the distributor. I've never seen, or had one fail, ever.

 

That Tahoe is exempt from emissions up here due to it's age. Will be a good excuse to slap another Edelbrock/HEI setup on there. At least the truck will be reliable after that. I'll be damned if I reward GM with my (or my buddy's) hard-earned dollars for designing this colossal failure-prone pile of dung. I'd burn the thing before it ever enters a dealership bay.

[sojatech]

Thanks for the replies. I got the truck back from the mechanic($407) and the gear is definately worn (pix). He put a remote camera on the cam and turned the engine to make sure that gear was alright. Was able to turn the oil pump with a screwdriver so that is alright, too.

 

He says there may be a problem on my camshaft, the truck is ready to retire soon. Good time for an oil change. I also have a small coolant leak in back of cyl 8. Bottom line is the engine has 200K on it and repairing these things cost as much as another truck.

 

I had a 1977 pickup and got 350K miles before I decided to sell it, mostly because I needed a 3/4 ton. That 350 cid just wouldn't quit. The only real engie work I did on it was to replace the timing chain. Thanks to PepBoys and their lifetime guarantee (back when) it didn't cost much to maintain, either.

[Doug_Scott]

Thanks for the replies. I got the truck back from the mechanic($407) and the gear is definately worn (pix). He put a remote camera on the cam and turned the engine to make sure that gear was alright. Was able to turn the oil pump with a screwdriver so that is alright, too.

 

He says there may be a problem on my camshaft, the truck is ready to retire soon. Good time for an oil change. I also have a small coolant leak in back of cyl 8. Bottom line is the engine has 200K on it and repairing these things cost as much as another truck.

 

I had a 1977 pickup and got 350K miles before I decided to sell it, mostly because I needed a 3/4 ton. That 350 cid just wouldn't quit. The only real engie work I did on it was to replace the timing chain. Thanks to PepBoys and their lifetime guarantee (back when) it didn't cost much to maintain, either.

 

Being able to turn oil pump iwth screw driver only shows you the pump is not seized. The pump may be a lot harder to spin at 1000 rpm. Is the coolant leak between the intake and head at the back of the engine? If so, pull the intake while the distributor is out and replace the gasket, and find a way to repair the coolant passage or block off on the intake manifold. Most engines with aluminum intake on cast iron heads will end up with some electrolysis damage to the aluminum manifold. As a temp cheap patch, you can clean up the intake manifold in the area where it is leaking and remove all corrosion. Once it is clean and dry, you can use jb weld for aluminum to cover the corroded part of the intake. Make sure you do not put too much on, keep it beneath the thickness of the gasket. Hard to describe this, but just remember that it cannot interfere with the gasket sealing intake to head. Let jb weld cure completely before installing intake.

 

That is not a permanent fix, and actually it is not even a fix, it is a patch that should last at least a year. Only you can say if the cost is worth the result. Changing the gear is pretty straight forward. You will need to drive the roll pin out of the existing gear, take the gear off and slide the new one on. The new one may not have the hole for the roll pin drilled all the way through. Put the gear on, line up the hole in the gear with the hole in the shaft, and then run a drill though the lined up hole, though the drilled hole in the shaft and then run the drill until the bit comes through the other side of the gear. Put the roll pin back in. Not sure about GM, but, Ford supplied a new pin with the new gear when I had to replace mine. Make sure you take note of how the gear was installed before removing it. It can be really easy to get the gear on upside down sometimes. The camshaft gear may be causing the fast wear on the distributor gear. Changing only the gear may last a year, may last forever or may last a couple thousand miles. As already said, only you can make that decision. If it was my winter beater, I would just change the gear and do an oil change. If it failed again before the winter was over, I would rethink the entire issue again and likely drop a cam into it, or just walk away and pick up another beater.