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Old    Jamie Corvin (Bumpass1)      Join Date: Oct 2010       09-25-2012, 3:47 PM Reply   
OK I have a total turd of a truck that I love driving for some reason. It is an '88 Chevy C2500 305ci. The thing is that in order to start the truck I have to floor it. It will start after a bit of cranking, but runs really, really rough. It will come down to idle but as soon as you feather the throttle very lightly it wants to stall. If you get on the throttle a little stronger then it will rev up and you can keep it running. When the RPMs are up it doesn't sound too bad, but as soon as you put it in gear it dies. I have replaced the plugs, cap, rotor, coil, ignition module, and fuel filter. I disconnected the fuel line and cranked it over to make sure the engine was getting plenty of gas. It appears to be getting plenty. I am excessively cheap and looking for someone to point me in the right direction. Oh yea, no codes thrown by the ECM either.

Any ideas???

Thanks
Old    RB (boardman74)      Join Date: Jul 2012       09-25-2012, 4:05 PM Reply   
Carb or EFI?
Old    Jamie Corvin (Bumpass1)      Join Date: Oct 2010       09-25-2012, 4:09 PM Reply   
EFI. Vin says carb, but I have never seen wires inside of a carb throttle body.
Old    Michael Hunter (mhunter)      Join Date: Mar 2008       09-25-2012, 7:27 PM Reply   
Check the EGR valve it might be stuck open?
Old    882001 (882001)      Join Date: Nov 2003       09-25-2012, 7:45 PM Reply   
fuel pump. its losing prime.
Old    RB (boardman74)      Join Date: Jul 2012       09-25-2012, 8:11 PM Reply   
Both good ideas and a carb could have wires running to it. If its says carb per the VIN and the numbers match, probably a carb. Your going to need to know for sure as you trouble shoot it.
Old    D H (dhcomp1)      Join Date: Mar 2010       09-25-2012, 8:55 PM Reply   
Quote:
Originally Posted by Bumpass1 View Post
OK I have a total turd of a truck that I love driving for some reason. It is an '88 Chevy C2500 305ci. The thing is that in order to start the truck I have to floor it. It will start after a bit of cranking, but runs really, really rough. It will come down to idle but as soon as you feather the throttle very lightly it wants to stall. If you get on the throttle a little stronger then it will rev up and you can keep it running. When the RPMs are up it doesn't sound too bad, but as soon as you put it in gear it dies. I have replaced the plugs, cap, rotor, coil, ignition module, and fuel filter. I disconnected the fuel line and cranked it over to make sure the engine was getting plenty of gas. It appears to be getting plenty. I am excessively cheap and looking for someone to point me in the right direction. Oh yea, no codes thrown by the ECM either.

Any ideas???

Thanks
Head over to the forum at Coloradok5.com

They specialize in these trucks. You'll get a lot more accurate info over there.
Old    Don Bethke (donb)      Join Date: Mar 2012       09-25-2012, 11:27 PM Reply   
You didn't mention the plug wires, very important.
Old    Kyle (RidingTheNW)      Join Date: Apr 2010       09-26-2012, 12:39 AM Reply   
TBI is a pretty simple system. Theres only a few sensors on the whole engine. The IAC (idle air control sensor) is a electric screw that controls the idle circuit only. Think of it as the choke. It bolts right into the throttle body. The TPS (throttle position sensor) is an electric sensor on attached to the opposite side of the throttle cable. All it does is send an electronic signal by voltage telling the ECU where the throttle currently is. If this sensor goes bad you will have RPM issues all over the place. The MAP sensor is the big square sensor located about a foot away or closer with a vacuum line hooked up to the throttle body that measures air pressure. The other sensors are the o2 sensors and the temp sender but those are probably not causing the problem. I would check the TPS and look for vacuum leaks. There are 2 types of TPS on the TBI systems. One is adjustable and has a rectangular plug with 3 wires and the other is a round plug and is not adjustable. If you have the rectangular plug, run a jumper wire to the middle wire and hook it to a volt meter and the other wire on the meter to ground. With the key on it should be at .64 volts. If its the round plug you cannot adjust it and I would recommend replacing it. If the TPS is not functioning properly it will not throw a check engine light. You may want to check fuel pressure too. Hope this helps.
Old    Cory D (cadunkle)      Join Date: Jul 2009       09-26-2012, 5:24 AM Reply   
Ditch the TBI and put a Holley on there, problem solved. Early GM TBI is nothing but headaches and a money pit to try to make it run right.
Old    Tyke Wilbur (dragracn)      Join Date: Jun 2008       09-26-2012, 7:06 AM Reply   
If it is TBI for sure, it sounds like the computer temp sensor is bad. This is very common on the early TBI systems, When the temp sensor goes bad it sends the computer a reading of -40deg obviously making the computer put too much fuel to the engine thinking its -40deg outside ( the reason you have to hold it wide open to allow more air in with the extra fuel to get it to start). It is a very easy fix, the sensor is rite beside the thermostat housing in the intake. unplug it, unscrew it, put in a new one, plug it back in, you will loose a little antifreeze when changing it, leave the cooling system cap on tight and the loose should be minimal.
Old    Jamie Corvin (Bumpass1)      Join Date: Oct 2010       10-01-2012, 3:53 PM Reply   
Well I finally got it running. Tyke was the winner, coolant temp sensor fixed her right up. Fires up runs smooth (kinda), ran it to the convenience store with my youngest kid. Got me there and back, so I'm calling it good. Thanks for the help guys!!
Old    D H (dhcomp1)      Join Date: Mar 2010       10-08-2012, 10:21 PM Reply   
Hey Jamie,

In the grand scheme of things, 90% of the comments above are total trash. Glad you got it worked out, but i'd head over to Coloradok5, as suggested above, with further questions.

Great group of knowledgeable guys over there.

Nothing wrong with enjoying an older rig like that, my 91 burb more than gets the job done!

Could i afford a 2000+ 3/4 ton burb? Sure! Do i want one right now? Nope!
Old    Daniel (cowwboy)      Join Date: Jul 2008       10-09-2012, 12:42 PM Reply   
My old tbi 305 actually had the connector to the temp sensor go out causing the same issue. That took a bit to figure out.
Old    Jamie Corvin (Bumpass1)      Join Date: Oct 2010       10-09-2012, 2:57 PM Reply   
Quote:
Originally Posted by cowwboy View Post
My old tbi 305 actually had the connector to the temp sensor go out causing the same issue. That took a bit to figure out.
Ended up being the same problem for me. As soon as I touched the connector it pretty much crumbled in my hands.
Old    Daniel (cowwboy)      Join Date: Jul 2008       10-09-2012, 9:43 PM Reply   
I wasn't so lucky. I replaced the sensor, still had the problem so after a few un needed parts and a employer who had a snap on pc we figured it to that simple part. Crazy what a temp reading can do.
Watching the injectors, they would pour fuel in at idle when it'd screw up.

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