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Old 05-05-2012, 12:01 AM
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95 350 tbi no start

Hello all, here's what I'm dealing with, 95 chevy 2500 with a tbi 350 and a 4L80E trans. Engine was replaced along with TB, distributor, cap, rotor, wires, plugs, battery, and starter. All of the work was done by someone else and was done before I got the truck a couple of days ago. When I first started it it cranked right up with an "ok" idle, when I put it in gear I could tell the timing was wrong because it would ping an knock even under a slight load, so I babied it 4 out of the 5 miles I needed to go then it died and now is extremely hard to start if at all and will not idle at all. I've set the timing at 0 with the brown/black wire disconnected with no luck, the only engine related fault code I get is 43, the scan tool said "ks problem" I'm guessing the knock sensor, would this keep the engine from running? What else should I look for? The spark seems intermittent or incorrect, if the dist is set at 0 it doesn't even try to start, if I rotate it clockwise as viewed from the top (about 1/3 full rotation) it starts and runs fairly smooth as long as I keep the pedal down a little, let off and it dies. This thing has me pulling my hair out, any help would be GREATLY appreciated!

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Old 05-05-2012, 08:32 AM
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Originally Posted by Ded0nfeet
Hello all, here's what I'm dealing with, 95 chevy 2500 with a tbi 350 and a 4L80E trans. Engine was replaced along with TB, distributor, cap, rotor, wires, plugs, battery, and starter. All of the work was done by someone else and was done before I got the truck a couple of days ago. When I first started it it cranked right up with an "ok" idle, when I put it in gear I could tell the timing was wrong because it would ping an knock even under a slight load, so I babied it 4 out of the 5 miles I needed to go then it died and now is extremely hard to start if at all and will not idle at all. I've set the timing at 0 with the brown/black wire disconnected with no luck, the only engine related fault code I get is 43, the scan tool said "ks problem" I'm guessing the knock sensor, would this keep the engine from running? What else should I look for? The spark seems intermittent or incorrect, if the dist is set at 0 it doesn't even try to start, if I rotate it clockwise as viewed from the top (about 1/3 full rotation) it starts and runs fairly smooth as long as I keep the pedal down a little, let off and it dies. This thing has me pulling my hair out, any help would be GREATLY appreciated!
Code 43 is for electronic spark control which does incorporate the Knock sensor.Some scanners kind of "abreviate" the code description and it can be confusing.
A code 43 sets with the tan/black wire disconeccted while setting timing.
Try clearing it and restarting the truck to see if it comes back.
Also if the timing was set at zero and you turn the distributor clockwise to get it to run, you are retarding the timing.turning the distributor 1/3 of the way means the timing is way off or the timing marks on the balancer are wrong, like incorrect balancer, or the outer ring has slipped.Also using the wrong plug wire when using the timing light will change the reading you get.Were you on the number 1 wire? Maybe you were on the number 2 wire?
They are next to each other on the cap back there and that would throw the timing marks way out if you were hooked to number 2 instead of number 1.
earlier models had a seperate spark control module, your truck has the electronic spark control built into the Ignition Control module.(inside the distributor)
The fact that when you get it to run OK but still not Idle makes me think you have a problem with the idle speed controller also.But the timing needs addressed first.

First thing to do is sort out the base timing issue, check the installation of the distributor make SURE you are on TDC #1 and compression stroke.do your best to get the piston at the top of the stroke so you can kinda gauge whether or not the balancer timing mark is right or if it has shifted.
Then get the distributor clock posisition correct, then be sure plug wires are on in the right tower and sequence, you know 18436572.
Attempt to set the static timing then at 0 degrees,then reinstall cap and wires and restart, be sure to clear the code 43 and have the tan/black timing wire connected . If it still runs crappy and sets the code,try unplugging the knock sensor to see if it changes anything. Then post back here.
The problem you have sounds compounded by a few things and you will have to start with the basic checks to sort it out.then go from there.
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Old 05-06-2012, 04:36 PM
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Thanks for the reply, I've tried getting the timing as close as possible (#1 plug removed, valve cover removed to ensure without a doubt I was on compression, even used a scope to make sure the piston was at tdc) the balancer seems right on, when I had the light on #1 I couldn't see where it was firing at all. I know some part of the system is working because the injectors pulse when the dist is turned, is there anything that would cause the spark to be intermittent? Do you know what wires/sensors/parts I should test for failure? I just dont have enough experience to diagnose this issue without good instruction, the sad thing is if it was a 07+ cat diesel it would be running down the road already. Thanks again for the help
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Old 05-06-2012, 07:27 PM
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Quote:
Originally Posted by Ded0nfeet
I know some part of the system is working because the injectors pulse when the dist is turned, is there anything that would cause the spark to be intermittent?
Absolutely. I have seen ignition control modules do exactly what you are describing.
The pickup coil signal gets handed to the PCM to run the injectors VIA the Ignition control module. As it passes through the Ig control Mod it is shared for the start/run circuitry in the Ignition Control Module to run the coil. After the engine starts a 5 volt signal switches the ignition trigger signal to a different circuit in the Ig Control Mod so the computer can regulate ignition timing , injector pulses are regulated by the raw(basic) signal from the pickup coil via the module. Somewhere in the module , the handoff circuit for the spark is failing.
Unless you can get the Ignition Module tested to be for sure it is bad or not,you will have to replace it. I have seen this paticualer problem several times on the TBI setup your truck has.
Oh and to be safe , I allways put a new Ignition coil in when I replace a module, because I have seen coils have a high voltage leak (spark shorts out) and it will kill the module.You can start with a coil, but chances are if it is shorting out the high voltage spark, the module took a hit allready.
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Old 05-14-2012, 08:42 PM
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Sorry it took so long to get back with you, I haven't had a chance to mess with it for a few days. I had tried another module I had laying around (the one under the cap) with no change, it was questionable though. When I get a chance I'll see if auto zone can test them. Thanks again!
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