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1991 Chevy S-10 4.3 TBI idle problems
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davidkirby777
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Jun 19, 2009, 12:35 AM
Post #1 of 13
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1991 Chevy S-10 4.3 TBI idle problems
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I have a 1991 Chevy S-10 2WD p/u. It has automatic trans, 4.3 V-6, a/c. Here is the problem:
At idle the engine runs very roughly. I have taken to a mechanic friend and he pulled no codes from the truck. It uses excessive fuel and I know we are getting cylinder wash as the oil smells like gasoline after a few thousand miles.
I did some research and found out that the first gen TBI had some issues. Mine is not the first to have this idling problem.
Here's what I have done to the truck to remedy the idling problems:
Replaced the following:
both coolant sensors (block and manifold)
O2 sensor
knock sensor
coil
plug wires
plugs
dist cap
rotor
map sensor
egr valve
rebuilt the TBI
fuel pump
fuel filter
battery
battery cables
alternator
ecm
idle air control valve
tps
checked all ground straps and connections to all sensors and valves, etc.
Some research shows that the ecm is giving commands to the TBI as if it were needing more fuel, i.e. there is an air leak somewhere in the intake system (manifold, etc.) and that's tricking the ecm to add more fuel. At speed the truck runs decent, although there is still the problem with more fuel being dumped into the intake. At idle, this situation allows for a very rough idle and when the truck gets to operating temp, it allows the engine to shut off.
I have gone so far as the pull the lead off one of the injectors at idle and the truck runs great. That leads me to believe that there has got to be an air leak somewhere as the ecm is reading that more fuel needs to be added.
So, I would be most appreciative with any comments, solutions or if anyone out there has seen this problem before or heard of it before.
Thanks,
David
p.s. I even thought that the power brake booster could be causing a leak-I will have that checked next.
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Hammer Time
Ultimate Carjunky
/ Moderator
Jun 19, 2009, 12:41 AM
Post #2 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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Is there a specific fuel injector that your unplugging to make it run better or will it work with any of them?
Is the check engine light coming on at all?
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davidkirby777
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Jun 19, 2009, 2:41 AM
Post #3 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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Hammertime,
In response to your questions:
It doesn't matter which of the 2 injectors I unplug, they do the same thing at idle, which is to say they make the engine idle better when at least 1 is unplugged.
The engine throws no codes, with the old ecm, or the one I got from another S-10.
Thanks,
David
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Hammer Time
Ultimate Carjunky
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Jun 19, 2009, 2:51 AM
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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There is really one one explanation for a result like that. The firing order has to be wrong. That is the only way killing cylinders could actually improve anything.
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Sidom
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Jun 19, 2009, 4:46 AM
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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Wow, that's a big list of parts. Do as Hammer suggests & double check your firing order & connections.....
I don't know what equipment you have but at this point I would really like to see a data stream & some exhauat gas readings. Your reasoning is good but a little off. A vacuum leak will make it run rough but not to the point of deluting the oil w/gas. Give it a vacuum leak & see how that makes it run @ idle, if better than it's too much fuel. There are a number of things that will overfuel it, ECT--coolant temp IAT--air temp, stuck O2, etc, this is where a data stream would come in handy. I would also verify your 5v ref. Pick any sensor that uses it (coolant or air temp), disconnect the connector & make sure you have 5 volts on the supply line. Also make sure you are getting the SES (check engine) light with Key on engine off.
It's really tough with out some hard data. I have seen firing orders off cause this exact problem. Normally you would think it would run rough all the time but I had one that just ran bad @ idle & smoothed out & didn't backfire @ higher rpms. So definately check all the basics before you move on.....
Footnote: I know a mentioned a component that I didn't see on your list. Please don't go & replace it. Do Hammer,s suggestion 1st, it's the quickest,easiest & cheapest. If it's off.....problem solved buy Hammer a beer, if not I gave you a couple of other things to check. But let's find the prob before you spend anymore $$$$$$. If worse comes to worse looks like Hammer has a real nice ride he can hook ya up with & you can off the truck...
(This post was edited by Sidom on Jun 19, 2009, 5:03 AM)
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davidkirby777
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Jun 19, 2009, 5:40 AM
Post #6 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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Hammer,
Appreciate your input, but I didn't kill any of the cylinders and the firing order is correct.
I think problem is too much fuel delivery at idle (less so at speed). I am very familiar with Fords but less so with Chevrolets, that's why I am trying to see if anyone has experienced the same, or close to it, problem.
Question:
How badly would a leaking power brake booster contribute to the symptoms?
Thanks for all your input!
David
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Hammer Time
Ultimate Carjunky
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Jun 19, 2009, 6:15 AM
Post #7 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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If you unplugged an injector, then you killed a cylinder. If the car ran better with a dead cylinder, then the firing order is likely wrong or it is crossfiring for some other reason. There aren't many things that will make a car run better by eliminating cylinders.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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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davidkirby777
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Jun 19, 2009, 6:21 AM
Post #8 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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I appreciate your input, Hammer. This engine happens to be an early generation fuel injection system. It has 2 huge injectors that sit on a throttle body in place of the carb. So when I unplug one injector, it doesn't kill the cylinder(s) it just reduces the amount of fuel going into the top of the manifold.
Thanks,
David
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davidkirby777
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Jun 19, 2009, 6:22 AM
Post #9 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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By the way Hammer,
very nice example of the '78 Pace car.
DK
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Hammer Time
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Jun 19, 2009, 6:28 AM
Post #10 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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I'm afraid your right. I didn't notice the year.
If the system is that rich, then the O/2s should be picking up on that. If they are not, then they could be clogged up. You really need a scan tool as Sidom said.
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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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jeff b
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Nov 27, 2009, 5:08 PM
Post #11 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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my dad is having the same problem i was wondering if you ever figered out the problem
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Hammer Time
Ultimate Carjunky
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Nov 27, 2009, 5:12 PM
Post #12 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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This thread is 6 months old. You'll do a lot better to start a new question of your own.
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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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jeff b
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Nov 27, 2009, 6:07 PM
Post #13 of 13
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Re: 1991 Chevy S-10 4.3 TBI idle problems
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i did do that i just added that since it was the same symptoms thanks jeff
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