Hello Boys, I have a check engine light that comes on after my pu warms up and is driven a little. I took it to the crysler shop (not dodge) and they put it on the obd it came up with no code but a message that said ( tourque management pulse) they tried to clear it with no luck and did not even know what it was. I have a 94 ram 1500 slt, 360 cid, 120k, 4wd, 46rh, with 3:55's, and p285 r16 tires, and it runs like it did when it was new. 13mpg town and 16-18 on th e road???also my gas gauge has been reading on the e mark and some time fluctuates a bit. but that happened a long time before the check eng. lite started coming on. Any help is much appreciated.
Thanks Mike

 

Thats wierd...I dunno much about OBD, I've only worked with OBD2 stuff, for all I know its the same thing. But usually they read off a code, not something like that. I would just take it to the dealer, or something else with a "good" daig computer when the light is on. After the light is off if stores it in its memory and that might make it read something other than a code.

As for the gas guage, you have a bed sending unit. You have to drop the tank to get to it (I think at least)

 

Just a WAG but it might be your fuel pump.

I have heard and experienced that when the sending unit goes bad the pump is not too far behind.

Could be the fuel pump heating up and the pressure fluctuating?

 

always check fuel psi for drivabilty concerns, can cause some odd things. including trans shifting problems.

 

With a 1994 your engine control computer is an OBD-I style that is different than the later OBD-II that showed up on Rams in 1996.

Your 1994 has an Exhaust Gas Recirculation valve (EGR) and a 'daughter' valve called the EGR Modulating Valve. 1992-1995 Magnum style 3.9V6/5.2 or 5.9V8 engines have this EGR system.

Something wrong with that EGR system would get my vote for what is causing your MIL light to come on after the truck is warmed up and apparently running fine.

After the engine is warmed up, the PCM computer 'checks out' the EGR system to see if it is working properly. It does the following:

1. It signals the EGR Modulating Valve to pass vacuum thru the hose to the EGR valve so that it lifts its pintle with the vacuum diaphram and allows exhaust gas to flow into the intake manifold.
2. As the exhaust gas flows into the intake manifold passages it displaces air, and with less air but the same fuel being squirted by the fuel injectors, this causes the mixture to 'go rich' and the air to fuel ratio drops from 14.7 to lower - like 13 or so
3. The PCM computer then 'watches' the O2 sensor to see if its voltage detects the rich mixture by going to a higher voltage, typically the O2 voltage will go from 0.45 to 0.9 volts or so
4. As the O2 sensor voltage goes up, the PCM computer commands the fuel injectors to squirt less fuel so that the air to fuel ratio drops back down to 14.7
5. After running for a little bit this way, the PCM computer commands the EGR Modulating Valve to cut off the vacuum in the hose to the EGR Valve, which causes the pintle to close and the exhaust gas to stop. Now air begins to replace the exhaust gas that had been flowing into the intake manifold. With more air, but the same fuel being squirted, the mixture 'goes lean' and the O2 sensor voltage drops from 0.45 to lower, like 0.2 volts.
6. The PCM now commands the fuel injectors to squirt more fuel so that the mixture will return to 14.7 and the O2 sensor gradually returns to the normal 'flickering' hight then low but with an average of 0.45 volts

If your engine's EGR passages become more and more plugged with carbon deposits, which is likely after 11 years, there will come a time when your PCM computer will give a failing grade to the above 6 step test. Your engine can otherwise be running fine.

Your engine can also fail the test if the rubber vacuum diaphram on the EGR has a hole so that it won't hold vacuum, or if any electrical wire has a broken connection somewhere, or if a vacuum line is bad.

The EPA requires that all the electrical plugs going to EGR system are 'fail safe' so that if anything is left unplugged the EGR system will turn on all the time, not stay off. When the EGR is on all the time, the idle is real rough and the engine may stall when you take your foot off the accelerator.

 

Excellent information. Thank you all. Now, I think we may be onto something with the egr system. Can you tell me how much vac. a healthy system should pull? and are the two egr valves located on the valve covers. Smaller valve on the left side and larger valve on the right side. looking at the motor from the front of the pu? Thanks, Mike

 

My warmed up 1995 (built Dec 1994) 5.9V8 pulls 18 inches of vacuum at idle.

The EGR valves are at the back of the engine, almost hidden.

The gear on the valve covers are the breather and the PCV valve - nothing to do with the EGR.