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Discussion Starter · #1 ·
Hello Everyone
I've looked and searched and generally kind of poked around here for a few hours trying to find something that could help my friend.
He purchased a nice Custom Chevy truck that someone had put a 94 LT1 Corvette motor and 6 speed transmission into it. The original owner had replaced a bunch of head gaskets and they would immediately blow one after the other and he got pissed finally and sold the truck to my friend. My friend had the Aluminum heads surfaced because they were warped and bought some new head bolts and took care of that problem.
The truck runs fine at normal operating speeds but when you get after it it pings really bad. He says it will still blow the tires off the truck through the gears but it just pings severely. At part throttle it's fine. He scanned it and saw about 38/40 degrees of advance at idle which seems high to me. He says that it cranks as though it has to much initial advance too. The truck idles with a very fuel rich smell. The truck does not have a working MAF Sensor but is setting no codes. The truck has no Knock Sensor. No Codes. I'm not sure if it has a working o2 sensor or not. No Codes set.
He said the computer had been sent by the original owner to a guy named Mark at Street and Performance. Can some of this stuff be programmed out so the engine just runs open loop all the time? I'm just trying to help him get his truck running properly. Any help is appreciated.
 

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Discussion Starter · #3 ·
Thanks for the reply.
Is it normal for the computer to run without the maf or o2 sensor and not set any codes?
That's what my buddy thought was weird and he uses some kind of snap on/mac tools device for reading codes on cars and trucks. I guess what I'm asking, do you think the computer has been setup to run with out these devises hence no codes thrown?
I also read on here that people were installing a lt4 knock sensor or some type of plug in lt4 box and were using that in conjunction with the knock sensor. I'm really just asking a few questions for my buddy.
 

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No, it's not normal for no codes to be thrown, but it can be tuned to ignore those codes and to run only in open loop.

With no MAF the computer runs in what is called "speed density" mode, which calculates the amount of air coming into the engines based on air temperature, manifold pressure, engine displacement, and engine RPM for fueling calculations, where a MAF measures incoming air mass.

The common upgrade when you have false knock (from roller rockers, headers, etc.) is to install an LT4 knock module in the PCM which is less sensitive to engine vibrations than the stock LT1 module. The same knock sensor is used.

I would absolutely install a knock sensor and O2 sensors and have it tuned at a minimum. A MAF sensor isn't a bad idea either, but speed density is fine if properly tuned.
 

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Discussion Starter · #5 ·
No, it's not normal for no codes to be thrown, but it can be tuned to ignore those codes and to run only in open loop.

With no MAF the computer runs in what is called "speed density" mode, which calculates the amount of air coming into the engines based on air temperature, manifold pressure, engine displacement, and engine RPM for fueling calculations, where a MAF measures incoming air mass.

The common upgrade when you have false knock (from roller rockers, headers, etc.) is to install an LT4 knock module in the PCM which is less sensitive to engine vibrations than the stock LT1 module. The same knock sensor is used.

I would absolutely install a knock sensor and O2 sensors and have it tuned at a minimum. A MAF sensor isn't a bad idea either, but speed density is fine if properly tuned.
I think you hit the nail on the head. This is exactly what I was looking for in terms of info. The previous owner did send the computer out to another guy to tune. I'll bet he did exactly what you were talking about to ignore those codes.

One more question. This Lt4 knock module, is it plug and play? Is it obvious where it goes or wires to /plugs in at? Can he get this module at a auto parts store?
Thanks so much for the help.
 

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Discussion Starter · #7 · (Edited)
An LT4 knock module is not something everyone needs. It is only needed if you are getting verified false knock from internal engine noise (like roller rockers). It is a GM part and while some people resell them, you won't find one at the local parts store. It plugs into a slot in the computer.

Gotcha Thanks

My buddy is going to check the cylinder pressure tonight too because he thinks he remembers the guy saying he either changed the cam or advanced it. If true that may be causing problems if nothing more than the hard to turn the motor over at start problem. I don't know what a normal cylinder pressure is for these motors but the heads on this one have been milled to make them flat and if the cam has been advanced it may be over 250 or 300 and that could surely be causing that problem. I feel like we are making progress here. One thing that hasn't been addressed is why it would be smelling so fuel rich at idle. I appreciate the help.
 

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Gotcha Thanks

. One thing that hasn't been addressed is why it would be smelling so fuel rich at idle. I appreciate the help.
without a MAF it is in speed density mode...which I suspect is why it is running rich at idle. I would add the correct year knock sensors (OBD1), MAF and O2 sensors and have the PCM tuned for the cam/mods the motor has.

I suggest communicateing with a tuner who is versed with LT1 as they can advise specific can and can't on the LT1 transplant your friend has.

I have always used Ed Wright at Fastchip but there are others out there.

The cam being possibly advanced "x" degrees will complicate the tune without confirming wtf happened there.
 

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Discussion Starter · #9 ·
without a MAF it is in speed density mode...which I suspect is why it is running rich at idle. I would add the correct year knock sensors (OBD1), MAF and O2 sensors and have the PCM tuned for the cam/mods the motor has.

I suggest communicateing with a tuner who is versed with LT1 as they can advise specific can and can't on the LT1 transplant your friend has.

I have always used Ed Wright at Fastchip but there are others out there.

The cam being possibly advanced "x" degrees will complicate the tune without confirming wtf happened there.

Thanks for the replys. You guys have been a lot of help.
 
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