Engine/Transmission (1998.5 - 2002) Powermax Fuel Light

[kdw75]

I have a PMax 2 and as I have been posting I have a surging problem at idle and more severe at about 2100 RPM. The green fuel light on the PMax gets brighter when it surges and I am wondering if the fact that it is doing that could tell me anything about the cause of the surging? I have ruled out the ECM, Crank Sensor and Boost (aka MAP) sensors, lift pump and injectors. I am also having the sound like the timing is changing sometimes unexpectedly. This all started when I picked the truck up from the dealer after they replaced a bad Crankshaft sensor and Map Sensor.



Thanks,

Keith

 

[Steve St.Laurent]

That fuel light gets brighter when the box is adding fuel. It adds fuel for one of two reasons - boost goes up, or more throttle is applied. I'd suspect either the MAP sensor or the wiring harness. This is one of the advantages of the PM3 with the remote display - you get to see what the box is seeing for boost. Mine was surging like that and my mechanical boost stage was rock steady - but the digital boost gauge on the pm3 was varying all over the place. I put dielectric grease on all the connections on the harness near the map sensor (tst harness) and it went away and the boost gauge was dead steady. It could also be an out of the box bad MAP sensor.

 

[kdw75]

Thanks for the info Steve. I know the MAP sensor is good because I bought a second one and put it in with no improvement. I just dread the thought of trying to troubleshoot the wiring and plugs on the MAP sensor. I guess I can hook into it with my meter and try to monitor it if that will be accurate enough. What kind of scan tool can tell you the sensor readings? Or can any of them do that?



Keith

 

[Steve St.Laurent]

Does your PM2 have a telephone style jack on the back of it? If so I believe you could just find someone who has the PM3 with the remote display w/gauges and borrow their remote. Plug it in and the boost feature should work - the EGT won't but the boost should. That way you would be seeing exactly what the PM3 is seeing after the harness, etc. A scan tool is only going to tell you what the PM3 is telling the ECM the boost is (which isn't what it truly is). You could call TST and verify if your box is capable of that or not with your box serial #.

 

[CCOLLAR]

I agree with Steve: check the PM MAP wiring harness. Sometimes the PM MAP ground isn't solid, which can cause the surging. Also, check the PM system ground wire for a good connection. Put dielectric grease on all connections.



Recall that the amount of fueling increase is a function of the MAP pressure. If the MAP voltage changes values (because of an unstable ground), the amount of fueling will change. Thus, you will experience a surge or lag.



If the PM is older (2 years old?), I believe TST offeres an updated MAP sensor wiring harness.



Call TST -- they are easy to work with and willing to help.



Craig

 

[kdw75]

Well, just for fun I unplugged the PMax and didn't even plug the MAP sensor in. Just left it unplugged and still had the surging. LOL I think that kind of eliminates that doesn't it?



Keith

 

[Steve St.Laurent]

What all did you unplug on the powermax? You have the pump wire, MAP harness plugs - the MAP sensor side and the engine harness side, 12v+ and ground. Exactly what did you disconnect?