'88 C2500 305ci HELP!!

[bumpass1]

New to the forum and in need os some help. I have an "88 C2500 that is running horrible. When cold I can start it up fairly easy, but it will idle rough. Once it warms up a bit it will idle better, but when you just touch the throttle it will die. Once she dies I have to floor it to get it to refire. If you punch the throttle when running it will rev up and sound halfway decent. When it will idle decently, the motor bogs down and dies when you put it in gear. So far I have changed the plugs, cap, and rotor, coil, ignition module, fuel filter, idle air control valve, and the throttle body gasket. It is not throwing any codes and I am at a loss as to what to look for at this point.

Any Ideas??

Thanks for the advice.

Jamie

 

[dyeager535]

I'd probably take the air cleaner off and look at the injectors before firing it up (turn key to run to prime the system), see if there is any fuel dripping. Then I'd fire it up and watch that the spray pattern out of both injectors is good.

Flooring it puts the system into "clear flood" mode, which is no additional fuel injected. If that helps, more than likely it's injecting too much fuel.

Could also be something along the lines of the coolant temperature sensor (in intake, not head) and you can verify that by hooking a real data scanner up to it, not a code reader. No idea if Autozone has those they can use, or just code readers.

 

[bumpass1]

I will give that a look tomorrow when I get home from work. Thanks

 

[Fordum]

Well, you have probably not wasted too much money. Most of the stuff you replaced was old enough to be getting ready to need it.

My only ideas at this point, are fuel pressure regulator and EGR valve. Like Dorian says, the flooring part sounds like its flooding out.

Watch for black smoke out the exhaust or a bright red glowing Cat if its running that rich.
Of course, dirty injectors might cause it too, so you would see dripping or a messy spray pattern like he said.

But, I would think that a rich problem like that would have set a code.

 

[bumpass1]

Forgot, I have changed the fuel pressure regulator also. I think it is running rich but it has not thrown the check engine light. the funny thing is that when I start it cold it will idle for as long as I let it, but as soon as I barely tap the throttle that is when it all goes bad.

 

[dyeager535]

Could even be MAP sensor to be honest. Really a good idea to get your hands on a datalogging device (even an ALDL cable and laptop) you can see if everything is within parameters without having to guess.

EGR testing is pretty easy, you disconnect it, plug the line, and see if the problem goes away. They ARE infamous for getting all plugged up and wreaking havoc.

 

[sweetk30]

ya i did some work on mine and forgot to hook up the map sensor vac line.

she fired up lumpity thumpity and real rich . ran great tho on full throttle .

finaly got under the hood and was ready for $$$ but found line off tbi and poped back on and bam 100% better.

all that and it didnt turn on a check engine light.

 

[dyeager535]

Yep. Way too much reliance from people anymore on the CEL "telling them" what the problem is. Not blaming the OP for doing this, just an observation. It is quite surprising what WON'T turn on a CEL, and then when one does turn on, how many things influence that code.

 

[bumpass1]

I know that the check engine lights are not the only indication of a problem and understand that the light does not come on with a lot of different situations. I was at a loss for what to look for in this problem. I was looking for a little guidance as what to look for next. I finally figured it out what was wrong with it. Ended up being the coolant temp sensor. I guess it was not passing the signal on to the computer to lean out the injectors.

Thanks to all for the help. I will not hesitate to post here again when needed. Great resource to have!!

 

[dyeager535]

Glad you found it! Hope I didn't make it sound like I was picking on you, that was not my intent.

I would much prefer people ask before spending a ton of money on parts that don't fix the problem...normally you can buy some sort of data scanner for less than the sum of the parts!