I posted a couple weeks ago, and thought I had my it solved... I was wrong. I have a '88 Ram with TBI. The engine will gallop anywhere below 1200 RPM, mostly when waiting and a stop light. Poor fuel economy, and throwing a rich mixture code. I have replaced the following sensors: O2, air temp, coolant temp. I also tested, and ruled out the MAP and TPS. There is no evidence that it is starved for fuel, and it has new ignition wires, plugs etc. I thought it could be a sticking valve, but then I realized that it gets better if I unplug the coolant temp sensor. Since the performance can be controlled by the sensor, I assume that there is no mechanical fault, and that whatever is going on is a result of the computer getting a bad reading, or giving a bad signal. Any ideas on what this might be? What are the normal effects of a bad computer? And also, since my truck is an 88, it may or may not have the old style TB, what are the issues associated with the early models? Im getting desperate here, as I have 2 weeks until I have to pass emissions. Thanks!

 

On a side note, it usually is pretty good until it reaches operating temperature.

 

Exactly what code is it showing?
What mileage are you getting?

As I told you before, you cannot test the MAP correctly without a separate controllable vacuum source. You also cannot test the TPS off the engine. If you are going to rule things out as the problem source you must do the tests correctly.

I can't figure out how you expect to pass an emissions test with all of your emissions gear not working. The bank of 3 solenoids that is disconnected controls the EGR, air switching, and canister purge system. You also say your air pump is inoperative. The air pump adds air at the cat and at the exhaust manifold or head to help insure total combustion of exhaust gasses. The O2 sensor is calibrated to take this added air into account. Without the extra air from the pump I would be surprised if the O2 sensor didn't read an overly rich exhaust gas.

Expecting these engines to run and read correctly with half the system disconnected just is not going to happen.

 

The TPS I tested on the engine, according to 2 manuals, and checked out ok.... the MAP sensor (and the 3 I have on the bench) all checked out ok as well, when I tested them WITH a hand vacuum pump. I replaced he EGR valve to ensure no leakage, and have hooked it up such that it doesn't require the solenoid circuit, but simply depends on vac pressure, which is what I have been doing for 3 years, and has not been the root of my problems. The other 2 solenoids in the bank do not affect the running emissions of he vehicle. The air pump is not engaged because I have 2 cats, and they no not have a air pump input. Whatever it is ha is giving me this problem is something that has happened in the last 2 months, and in this time, none of the emission equipment has been changed, that is why I am confidant my problems lie elsewhere. My fuel economy has dropped from a regular 13 MPG to about 6, and he computer is throwing only one code, which is code 52.... rich air/fuel mixture. I also have a lack of power, but no lack of fuel. Also, I ask again, I know there were TB's that were known to be bad in '88, what exactly are the symptoms of his? I have an 89 TB as well, is it worth changing it?

Thanks

 

Ok, so here is the update. I hooked up all the emission equipment to spec.... tried running the truck, and it drove well, much better.... the EGR valve made a difference.... however, while it is idling in park on the drive, it sounds perfect.... then if I give it a quick rev and let it go, it will gallop about 4 or 5 times before the idle levels out again, almost dies, but always catches. It is also still throwing the rich code. I am wondering if maybe something is telling the computer that it is running rich intermittently, and causing it to run lean all the time.... I feel like there is a slight power loss...

Its getting better, but still not quite there...