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Hope you guys can shed some light, My dually is an 88 r30, it has a 4 speed, 454ci with TBI. My problem just started, when I first start my truck up it is running very rich to the point it will burn your eyes if you stand to close for very long, it idels pretty smooth and will maintain an idel without any problem, while it is ideling it will show some smoke from the exhaust very little but still some comes out. If you drive the truck for any extended period of time when you come to a stop it will idel down very low and in most cases stall out, it will start back up with no problem. I have already replaced the MAP sensor and the coolant sensor and that did not solve the problem. I am looking for ideas on what else it could be. I just started this almost like a switch was flipped, Both of my gas tanks are brand new with new pumps and screeens in both tanks and my tank selector switch is also new. Any help would be graetly appreciated. Thanks in advance.

My 87 did the same thing. After seeing the top end of the motor, I know why mine was the way it was. Mine was just a case of old and worn out and neglect.

We did a minor tune up a couple of months ago. Plugs, wires, rotor bug etc. Made it run a little better for about a week, then right back to where it was before.

My motor is new only has approx 10,000 miles on the rebuild, It is very well maintained only the best fluids all royal purple synthetic, just installed new wires and plugs, fuel filter ect.

Do you have access to a scanner? You might need to look into having it scanned, so you can see what everything is doing in real time. If the CTS did not solve the problem, it may be the IAC, or TPS way out of adjustment. My money would be on the CTS (should be on the intake) causing the truck to think it is really cold, and just dumping fuel. The new sensor could be faulty.

I dont have a scanner but I am sure I can find one. I assume when you say CTS you are referring the the coolant temp sensor? Which I just got from GM yesterday and installed last night along the the MAP sensor do I need to unhook my batteries and reset the computer after having installed these two sensors? When you say IAC what are you referring to? Could it have anything to do with the EGR valve?

Just because you just bought a part or just replaced it doesn't mean it's "good". Most of the time, yes they are good, but sometimes you can get a faulty "new" part. It wouldn't hurt to swap it out with another one just to rule it out before you move on to other parts and more money.

Quote:

Originally Posted by LOW1TON (Post 4099753)

CTS-Coolant Temp Sensor. That is the one in the intake (usually at the front. This is different than the engine temp sender, which sends information to the gauge (usually in the left cylinder head). If it is shorted, the vehicle thinks it is -20 outside, and it is sending extra fuel to get to operating temp. The IAC is Idle Air Control, and it is on the throttle body (it will have a square, 4 wire plug). This is a stepper motor that regulates the flow of additional air under the throttle blades. if it is dirty or broken, it will either not let enough or too much air in, and the computer will try to compensate by adding or pulling fuel. I would pull the throttle body and clean it really well, and unscrew the IAC and make sure it is clean, too. You shouldn't have to unhook the battery to reset the computer, it will do it as you are driving. EGR shouldn't have anything to do with a rich idle.

By watching what the sensors are doing on the scanner, you can get an idea of what the computer sees happening. If the CTS is showing a negative reading, you will have a problem with the sensor or the wiring going to it.

Thanks for the feed back, it all seems to make some sence. Is there any palce you can buy a fully rebuilt TBI unit that would have come factory on these trucks? One that will already have new injectors installed?

i have an 88 r3500 also and have been experiancing some of the same problems. I have made several calls and finally got ahold of a place called cfm enterprises and they gave me lots of good info. according to them on of the big problems is the pressure regulator. The informed me that there can be as much as 4 lbs variation on factory style fuel pressure regulator. they reman tbi s and put adjustable regulators on them which can be set at the 14 psi which is optimal for our trucks.

I think JET used to do them, but you may not need a whole unit. The pulse width of the injectors is computer controlled. If they are flowing (and it looks uniform) then it is probably not an injector problem.

I know it sounds crazy but I am one of those guys who does not mind replacing old parts with new ones even if the old part still seems to be ok. It is kind of a piece of mind thing with me knowing the parts are new. That is kind of the way my whole truck has been built if I get to an area that parts have not been replaced and something is giving me issues in that area I will go through and replace all of the parts with new ones. The unit with the built in regulator sounds like it might be the ticket, but I will get hooked to a scanner first and see what it shows. I went ahead and replaced the EGR valve today just out of piece of mind.

i got the name wrong it is cfm-tech.com