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1992 Chevy Cheyenne Chokes

Tiny
HCOHLER
  • MEMBER
  • 1992 CHEVROLET CHEYENNE
  • V8
  • 2WD
  • MANUAL
  • 180,000 MILES
I purchased the vehicle and it ran excellent for about a month or two. Then after a 30 mile drive I stopped at a store and shut it off. After leaving the store and about a mile or two later it started misfiring and running rough. I used trial and error with the emissions system on top of the engine, purchasing new parts, and checking hoses. The only thing that works is unhooking the hose that connects the map sensor to the back of the throttle body. It still stalls if you don’t keep the throttle slightly open and it uses a lot of gas.

Please help, my head hurts!
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Tuesday, May 12th, 2009 AT 12:51 AM

11 Replies

Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Ok I need to know if you truck is a 1/2 ton or larger and what engine is in it? Do you have a digital multi meter so we can test a couple of sensors? What did you replace I need to know to be helpfull ok, the more you tell me the less we do repeat work. Thanks and get back to me and we will go from there.
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Tuesday, May 12th, 2009 AT 10:15 AM
Tiny
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It's a 3/4 ton with a 5.7 L 350 and has throttle body injection. I have a digital meter and have checked voltage on a couple of the emission parts and harness. I have replaced MAP sensor, Idle Air Controller, Spark Plugs, and have tried switching out some of the others. The only thing that allows it to run is unhooking the vacuum hose that connects the MAP sensor to the bock of the throttle body and then it runs really rich. If the hose is connected it chokes as if it is not getting enough air.
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Tuesday, May 12th, 2009 AT 1:51 PM
Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Ok it isn't chocking it don't have a choke it used sensor to enrichen it at cold start. Now I do need you to tell me what all you have replaced, you said you tryed switching out some others what others? How old is the fuel filter? How clean is the air filter? Get back to me with everything you know so I can be of better help. Thanks.
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Wednesday, May 13th, 2009 AT 10:46 AM
Tiny
HCOHLER
  • MEMBER
  • 6 POSTS
What I mean by choking is it seems to not be getting enough air (eg. When the MAP to back throttle body vacuum is off it runs ok and drinks gas.) Replaced MAP, IAC, Oxygen sensor, TPS, Fuel filter, Air filter, and checked the EGR. What I mean by switching out is that I went to the junk yard, collected some parts, tried them out, and put the old parts back on.
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Wednesday, May 13th, 2009 AT 5:56 PM
Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
Thanks for clearing that up now with that have you checked the fuel pressure? I suspect that it may be running lean. How much vacuum does it have? Let me know what the fuel pressure and vacuum is so we can figure out where to go.
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Thursday, May 14th, 2009 AT 9:55 AM
Tiny
HCOHLER
  • MEMBER
  • 6 POSTS
I haven't checked the vacuum pressure or the gauged fuel pressure. However, I just took the TBI off and am inspecting it for the second time. I don't like the fuel pressure regulator design and am curious to know if that is a common problem. It could be drowning itself and when I disconnect the MAP to TBI vacuum hose it breaths extra air and runs rich. When I do that it drinks fuel and some black smoke is visible from the tail pipe. What tool do you recommend to check line pressures?
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Thursday, May 14th, 2009 AT 4:09 PM
Tiny
RACEFAN966
  • MECHANIC
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OK there is an adapter you need to buy that goes inplace of the fuel filter that gives you a shrader valve to connect a fuel pressure tester too it is needed to do this. Now as for you pressure regulator yes they do have a common problem they brake the spring inside that works the diaphram that controls the pressure keeping it at the 15 psi or so that is needed. However if the spring is broken you can't buy them at you local parts store and they are not part of the regulator kit. Let me know what you find.
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Friday, May 15th, 2009 AT 8:20 AM
Tiny
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  • 6 POSTS
I did some research and found out that the fuel pump was a common problem. I bought a TBI rebuild kit and rebuilt it overnight. I accidently broke the TPS and also bought a new one of those for the second time. Overnight, I went over some fluid mechanics in my head and came up with a couple of possibilities. I suppose in this case that less pressure equals more velocity and thus equals more flow or volume, which would explain the rich fuel mixture. I also recalled some pump formulas that have to do with pressure and decided to buy a fuel pump just in case. I put on the TBI and it was doing the about the same thing as before, so I unhooked the MAP to TBI hose and it ran better with a slightly different feeling do to the new TPS. I got a good look at the injectors and the exhaust, which were flowing rich with some black smoke. I then decided to put the fuel pump on and did so. It runs a lot better than it did but not better than it was. It seems to be running lean with a very low idle as far as I can tell. However, I still want to get it to where it was.
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Friday, May 15th, 2009 AT 5:19 PM
Tiny
RACEFAN966
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OK have you checked the coolant temp sensor? If not then what I need you to do is unplug it and check the ohm's of the sensor (not the wire harness). Now if you do this cold then what I will need you to get back to me with is the ohm reading and the outside temp at the time of the temp. Let me know what you get.
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Saturday, May 16th, 2009 AT 8:59 AM
Tiny
HCOHLER
  • MEMBER
  • 6 POSTS
I gave it an oil change, made some adjustments, and now it runs excellent.

Thanks for the help

P.S.
Probably should of bought a Ford, however, bought a Chevy instead.

Buy American unless of course you can buy German.
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Monday, May 18th, 2009 AT 1:19 PM
Tiny
RACEFAN966
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Great glad to hear that is runs as it should. I would agree with you but then again I own Fords too and I ran the vin numbers to make sure they were American. Thanks and if there is anything else just ask.
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Tuesday, May 19th, 2009 AT 9:11 AM

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