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Discussion Starter #1
Ok I'm at a loss,I have a '90 Suburban 4wd, 350 with TBI,I have had the motor and exhaust custom built at a shop here in town, the entire engine is new and the TBI has been rebuilt now I have a gremlin that I cannot figure out. If I have the trans in OD on the free way the motor chugs and looses power, it also chugs and misses if I'm going up a steep incline no matter what gear I'm in,it also pulses when idling my RMPs go up and down. The knock sensor is new and so is the electronic spark control module and nothing seems to help,nothing shows up on my code reader.I also disconnected ESCM and yet no code appeared,I am lost,I initially took it to the mechanic who built the motor but he can't seem to find the issue.Any thoughts anybody?
 

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When you said the engine was custom built what all was done to it, cam, head work etc...?? If a cam does it match the torque converter? We need more info about the engine mods.
 

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Discussion Starter #3
Engine Mods

Double roller chain, hypereutectic pistons, high volume oil pump, comp cam 12-388-4, edelbrock med rise intake. No trans work has been done yet.
 

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I would call CompCams tech line and see if that cam works with a stock transmission converter. If it does then we have to look elsewhere for your problem. the other mods seem fine.

---------- Post added at 06:13 PM ---------- Previous post was at 06:08 PM ----------

Also ask CompCams if the cam works with the stock computer or does the computer need to be reprogrammed. When you say custom exhaust is it dual and did you install new cat/cats?
 

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Discussion Starter #5
Mods

The exhaust is dual into single 3 inch exhaust new cat with 2 stage Flowmaster,I'll have to call Comp on Mon. and check about the torque conv.
 

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Don't forget to also ask them about if the cam works with the stock computer chip. I know Edlebrock includes a new chip with there performance pack (it has there cam, intake and headers) for your truck.

---------- Post added at 07:01 PM ---------- Previous post was at 06:52 PM ----------

I looked at CompCams website and it says that cam is computer compatible and I looked at the spec's and its not a wild cam and should be fine with the stock conveter.
 

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Have you checked your fuel pressure or replaced your fuel filter? Pulling a steep hill, & bombing down the freeway at higher speeds are 2 times when your engine would need more fuel & maybe it's not getting it
 

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My truck was doing the same thing a while back, no serious modifications, stock cam. I tracked it down to several problems causing it, the biggest one was a weak ignition coil, second problem was a clogged EGR, third was the TCC solenoid was getting weak, this allows the torque converter to become more efficient(engaged it makes it more efficient for when you gun it, or need more power transfer) or less efficient( when you are coasting, or keeping a constant speed, or idling, it disengaged to become less efficient, and allow slip so to speak).

I haven't replaced the TCC yet, but the best way I've found to prevent it is to put it in drive until the engine gets to operating temp, then put it into overdrive, it wont happen(slip/chug) unless you just constantly mash on the gas.

^ I don't think putting a different cam would really affect the torque converter, OBD-1 doesn't really care what you do to the engine, as long as it's within it's specs, which a cam wouldn't really mess with any of the engine specs affecting the tranny. I don't think at least.
 

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My 92 GMC Sonoma GT with a 4.3 Vortec running OBDI has many of the same problems at the moment. But it comes up with Code 43 which is the Electronic Spark Control is messing up and the coolent sensor circut has been open for longer than 5-6 seconds. My timing will become nearly 20deg retarded and will have no power or will be running advanced some as noted by improved performance and die in the heat. Although it is not overheating because the sensor to the gauge is in the passenger side head, gauge working correctly, and ECM temp sensor is on the front behind the alternator bracket by the thermostat. I'm wondering if it is a componet heating, expanding and breaking a connection that causes this because my truck has Eldelbrock headers as well and there is a lot of heat in the engine bay.
 

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Discussion Starter #11
Found out code 43,while the book says is ESC,all I had to do was replace the connecting wire to the knock sensor as the connector is just a small pin like insert inside a plastic housing and are apparently prone to failure from what my mechanic was telling me,so after I replaced the connector then I found one of my spark plug wires was arching to the exhaust manifold heat shield,replaced and re-ran my plug wires now the Burb runs like a beast.I even needlessly replaced the ESC. Just another example of looking for the most complicated problem when something simple did the job.
 

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I just found one of my wires arcing too through a cut in the boot over the wire-plug cuppler. It was my number 1 cylinder at that. Fixed it now it runs a lot better. Just need to find some non conductive heat shields for my boots because it's a tight fit between my headers and boots. I don't want this happening again.
 
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