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moody
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Dec 26, 2012, 3:14 PM
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1991 chevy 4.3 V6
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I bought a sandrail with a chevy 4.3 V6 tbi that idles good but rich! Off idle about 1100 to 2500 is stumbles and then clears up and runs great on the top end! I think it has to do with the computer but not sure where? I found the there was no O2 sensor but I installed one and it did not help! What can I check that maybe I'm missing? It doesn't look like he has all the sensors hooked up but i havn't found a diagram to fallow yet?
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Tom Greenleaf
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Dec 26, 2012, 3:31 PM
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Re: 1991 chevy 4.3 V6
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Probably me, but what the heck is a "sandrail" for a vehicle and did this engine belong in it to begin with? If not it's trouble and plain not having everything hooked up with or without some exacting diagram of everything is already trouble. Even 1991 needed things all properly in order or stuff isn't going to work right,
T
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Hammer Time
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Dec 26, 2012, 3:56 PM
Post #3 of 30
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Re: 1991 chevy 4.3 V6
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This is a fuel injected engine. I assume you still have a computer. Do you have an operational check engine light and diagnostic connector?
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moody
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Dec 26, 2012, 5:33 PM
Post #4 of 30
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Re: 1991 chevy 4.3 V6
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There is not check engine light and as far as I can tell I don't see a connector to the ecm! Do you know if the engine has a knock sensor or anything like that I should look for cause I new there had to be an O2 sensor!
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Hammer Time
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Dec 26, 2012, 5:37 PM
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Re: 1991 chevy 4.3 V6
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A knock sensor would have nothing to do with a problem like that. You're going to have to find a way to access the data in the computer to have any idea what is going on. You can start out by checking the fuel pressure with a gauge. They made 2 different 4.3 engines that year, a Vortec and a TBI and the pressures will be different.
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moody
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Dec 26, 2012, 5:45 PM
Post #6 of 30
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Re: 1991 chevy 4.3 V6
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I did check the fuel psi already too lol! I think your right I'll have to pull the ecm and see if theres a way to check it! I was hoping I wouldn't have to do that its looks like a pain to get it out lol! Thanks Hammer
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Hammer Time
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Dec 26, 2012, 5:47 PM
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Re: 1991 chevy 4.3 V6
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OK, what was your fuel pressure?
Pulling the ECM isn't going to do anything for you. You need a diagnostic connector for access.
If they used the original wiring harness, it should be somewhere.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Dec 26, 2012, 5:48 PM)
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Discretesignals
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Dec 26, 2012, 5:49 PM
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Re: 1991 chevy 4.3 V6
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Sounds like a real nightmare if half the stuff is missing on it.
Some of those sensors are critical. O2 sensor or knock wouldn't be one. Ones like the coolant temperature sensor, TPS, MAP, and distributor ref and low signals are very important signals the computer needs for proper operation of the fuel injection and ignition timing systems.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 26, 2012, 5:53 PM)
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moody
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Dec 26, 2012, 5:56 PM
Post #9 of 30
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Re: 1991 chevy 4.3 V6
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I don't see a coolant sensor but the map is good! and the distributor are hooked up to an MSD igntion! It does run rich on the bottom end but great on the top! What should I start with now you think?
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Discretesignals
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Dec 26, 2012, 6:04 PM
Post #10 of 30
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Re: 1991 chevy 4.3 V6
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Well, as HT stated, it sure would be nice if you could find the ALDL connector. You could roll it into a shop that has an old GM tech 1A or equivalent and plug in and watch the datastream and pull any stored codes. That would make finding out what the computer is missing a lot easier. The only other option is pin checking the signal circuits of all those sensors to be sure the signals are getting to the ECM and they are legit.
You really need to find a tech that can check out what you have, so they can figure out how to test it. Can't tell you how to test it without actually being there. It may not even follow a manufacture's wiring diagram since it has been modified.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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moody
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Dec 26, 2012, 6:08 PM
Post #11 of 30
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Re: 1991 chevy 4.3 V6
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Ok I'll see what I can do and let you know what happens thanks again for your help!
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Hammer Time
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Dec 26, 2012, 6:11 PM
Post #12 of 30
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Re: 1991 chevy 4.3 V6
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We'd still like to know what the fuel pressure was. too
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Sidom
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Dec 26, 2012, 10:06 PM
Post #13 of 30
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Re: 1991 chevy 4.3 V6
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How do you know the map is good?.....If this doesn't have a coolant temp senors installed then your wasting your time trying to solve a rich running condition, that's one of the primary inputs....
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moody
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Dec 27, 2012, 7:15 AM
Post #14 of 30
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Re: 1991 chevy 4.3 V6
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I tested the fuel psi it was 13 lbs in and 3psi on the return! Ill look today to see if theres a connector to the ecm!
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moody
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Dec 27, 2012, 7:19 AM
Post #15 of 30
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Re: 1991 chevy 4.3 V6
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I'd like to find the stock wiring diagram for the truck if you know where i could get that i think it could help me cause i could find witch lead go's where from the ecm!
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Hammer Time
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Dec 27, 2012, 7:28 AM
Post #16 of 30
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Re: 1991 chevy 4.3 V6
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Wiring diagram fro what? Do you have any clue what vehicle it was originally from?
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moody
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Dec 27, 2012, 7:33 AM
Post #17 of 30
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Re: 1991 chevy 4.3 V6
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Yep it came out of a 91 1500 chevy its all stock other then a tbi spacer and the MSD!The only thing I really done so far was the exhaust!
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Hammer Time
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Dec 27, 2012, 8:22 AM
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Re: 1991 chevy 4.3 V6
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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moody
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Dec 27, 2012, 8:32 AM
Post #19 of 30
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Re: 1991 chevy 4.3 V6
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That is great thank you so much I will check it out when I get home! I've been trying to find that for a few days lol!
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Hammer Time
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Dec 27, 2012, 8:45 AM
Post #20 of 30
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Re: 1991 chevy 4.3 V6
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Unless you really understand how all those circuits work and what is acceptable, your best bet is still to find a way to plug in a scanner. The connector has to be there somewhere if they didn't cut the wires.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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moody
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Dec 27, 2012, 8:48 AM
Post #21 of 30
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Re: 1991 chevy 4.3 V6
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I will check it out tonight and let you know thanks again!
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moody
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Dec 28, 2012, 7:09 AM
Post #22 of 30
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Re: 1991 chevy 4.3 V6
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Good morning Hammer I found the problem with the running because the wire diagram u gave me was awesome! The TCC control was connected to the ground and the EGR was not hooked up! It seems to run alot better just sitting there but ill really know when I drive it soon! Thanks again for your help!
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Hammer Time
Ultimate Carjunky
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Dec 28, 2012, 7:12 AM
Post #23 of 30
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Re: 1991 chevy 4.3 V6
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The EGR not being hooked up with only cause some pinging at worst and the TCC shouldn't effect anything beyond the transmission unless it is stuck on and then it would only run in Park.
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moody
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Dec 28, 2012, 7:17 AM
Post #24 of 30
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Re: 1991 chevy 4.3 V6
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I seems to idle better and its not stumbling off idle! but there is something though! on the diagram it says D2 is a TPS & CTS sensor ground is black but on my car its purple and it go's to the map sensor!
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Hammer Time
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Dec 28, 2012, 7:23 AM
Post #25 of 30
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Re: 1991 chevy 4.3 V6
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The diagrams I gave you were supposed to be for TBI system.
These are labeled "auto trans" but appear to match what you have.
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