Timing Chain Jumped?


Old 08-26-03, 10:11 AM
Antony W. Serio
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Question Timing Chain Jumped?

I have a 1988 Chevy S-10 4x4 automatic with a 4.3 V6 and 256K miles. The other day, the truck just died at my mailbox while I was trying to start. She ran for about half a second then died. After that, she would crank strong but wouldn't catch. I checked the OBD codes all I came up with was '12' which is normal. Spend the rest of the day checking electrical connections and vacuum lines and replaced the fuel pump relay in the off chance that might be causing the problem.

The next morning, I cranked the engine just to see if the battery still had enough juice to turn over, and she started right up. The engine sounded strange with a 'ticking' noise, but I put her in gear and got her the rest of the way home and into my driveway. I then re-checked everything that I had done before, and was able to get her started one more time, although her engine was still ticking. After that, I was back to where I was before with the engine cranking, but not starting.

I described my symptoms to my mechanic, and he said that it sounded like my timing chain had jumped a few teeth. Is there a way for me to check that without dismantling my engine? I know I can use a timing light if I can get her to run again, but I don't know how to check the timing on an engine that won't run. I have heard of people using a flashlight jerry rigged with a set of leads to time old Volkswagens, but I don't think that will work on a truck with modern ignition. Does anybody out there have any ideas?
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Old 08-26-03, 10:14 AM
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At 256k a chain and gear set surely wouldn't hurt! .

Many of those had nylon gears and give up the ghost LONG before that time.

Do the water pump at the same time.

How much play is in the distributor rotor? That will tell you to some degree how much stretch there is.
Old 08-26-03, 08:02 PM
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Remove the number 1 spark plug (front plug, driver's side). Remove the coil wire. Put your finger on the spark plug hole, and have a helper "bump" the engine (meaning use the key to act like you're starting the truck, but quicker, and release the key many times) until you feel a solid puff of air come out of the spark plug hole. Remove the distributor cap, and see if the rotor button is pointing to where the number 1 plug wire was. You most likely will have to put a socket and rachet on the big center bolt of the harmonic balancer to get the mark of the balancer/belt pully to line up exactly on the 0 degree mark of the front timing cover. Again look at the rotor button to see if it lines up where the #1 plug wire was. If your distributor cap has the wire towers sticking straight up, it helps to make a light mark on the distributor where the #1 wire is BEFORE taking off the cap. If you cap is flat, with the wires connecting straight in from each side, you'll have to look in the bottom of the cap to see where the #1 electrode is, as these caps are "off set" inside..
A VERY small amount of variance is ok.. a 1/4 inch or more is trouble.
After seeing whether the rotor is pointing correctly, use the socket and ratchet to move the crank shaft. Turn the crank clock-wise until the rotor moves. (do this slowly). Then reverse the direction of the ratchet, and turn the crank counter-clockwise. Note how much it takes from the beginning of the counterclock wise pull, until the rotor button begins to move.
Also, these engines are bad about shearing distributor drive gears..I'd much rather pull the distributor if any excessive slack is found, before pulling the front off the engine.
Old 08-27-03, 03:08 AM
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I doubt the timing chain jumped if you started right up the next day and ran fine. As far as the ticking, is it abnormally loud? Or does it sound like it is coming from the fuel injector? Did you check the oil level? When it dies, have someone crank it and check for spark, and injector pulse. If you can identify the tick, I'd suspect a pick up coil or module may be at fault. This is assuming you did all of your preliminary checks.
Old 09-01-03, 04:18 PM
Antony W. Serio
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Well, I checked for spark but didn't see any. After digging a bit deeper, I replaced the ignition module, rotor, and distributor cap, so now I have spark. However, my truck still wouldn't start. My mechanic suggested that I may have flooded the engine, after attempting to start too often without a good ignition. I checked the plugs and they were soaked in gasoline, so I changed them as well (they were not in good shape). Unfortunately, now I am back to square one. I know I have good spark now, and I am pretty sure that I my fuel is good because my spark plugs were wet with gas.

All of this leads me back to what my mechanic originally suggested, which was timing. Now, my plugs were less than a year old, yet in addition to beging fouled with gasoline, some had very bad scoring on the center electrode and insulator, and one plug actually shattered as I was removing it. Would questionable timing damage my plugs in this manner?
Old 09-02-03, 07:55 AM
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If you spray some Gumout into the throttle body when someone cranks, will it backfire or attempt to run????

What is the fuel pressure? Again, you're up there in mileage, a timing chain WOULD NOT be a bad idea , but get to the root of the problem first.

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