I just installed a PowerFC last week and I'm having trouble with the MAP (PIM) signal. Sometimes it will jump right to 4.85v (1.12 kg/m^2) and when that happens the engine stalls. I can make the correct signal come back by wiggling the bundle of wires behind the ECU. So the problem is intermittent and I'm reluctant to drive the car much in case it stalls somewhere bad.

The big question I'm trying to understand is:
What kind of wiring faults might a +5v signal be caused by? (Open circuit? Short circuit? Bad ground?)

 

That's odd; I would have thought it would have toggled between 2.6V and 0V if it was a wiring problem and engine off but ign on. The only other thing is there must be an intermittent short with some wire in the same connector 1 harness. This input is set for 0 to 5V and a short with 12V may still only indicate around 5V. I would strip that connector harness back a ways and look it over. The only other possibility is a problem with the PFC; might want to borrow another and isolate from there.

 

I think if the PFC sees the MAP sensor unplugged it shows as 5 (or 4.85 whatever) volts. So, if it's dropping signal, there's your problem.

I doubt it's the 5v feed to the MAP sensor, I believe that same 5v feed goes to other sensors as well. If that was flaky you'd have multiple sensor failures. Same goes for the ground.

Most likely it's just the wire to the PFC. Is your PFC used or new? Did you have any similiar problems with the stock ECU? Could also be the pin in the connector to the ECU.

Dale

 

An open circuit could cause the MAP signal to measure 5V, assuming the PFC has certain circuitry inside to detect an open circuit. As mentioned by Dale, you could easily disconnect the MAP sensor plug with the engine off to check. A problem with the sensor ground would also cause the MAP signal to measure 5V, but it's likely it would also cause other sensors to measure 5V (possibly TPS, CLT, and AIT). A short to +12V (or to other solenoid or injector signal wires that sometimes carry 12V) could also cause the PFC to measure 5V.

 

The PFC is brand new. The emissions harness is about 4 years old (like new) and the front harness is original. I definitely hope the issue is not behind the dash.

I had a stock ECU and aside from a mostly non-working tachometer, everything was good until I installed the PFC.

 

You are dropping the signal from the MAP sensor. If the problem is "fixed" by wiggling a bunch of wires by the PFC then you certainly have a loose wire(s). Start by disconnecting the PFC, press down on the lock tabs and use a small screwdriver to remove the connectors, do not just pull on the wires. Inspect every wire for damage or loose fit in the connector bodies. When reinstalling the connectors press firmly to ensure a locked fitment and verify that none of the wires are not partially pressed out. Specifically look at the wires in connector 1 since the G/Y wire 1O is the map signal. While you are down there look at the blue X-05 and make sure that all the wires are in good condition there as well.

 

Thanks, that certainly aligns with my symptoms.

I've tried in the past and with this install to avoid pulling on the wires, but the design of the connectors on the ECU and the amount of force required to remove it leave you few options. Mostly I've pulled gently on the wires with the latch pressed and wiggled the connectors and used a flathead screwdriver to get the connector to begin backing out. It's entirely possible that I let the highly cramped environment and grippy terminals get the best of me and I've simply pulled too hard on the wires at some point.

Do you know if the terminals in the harness connectors can be replaced?

David

 

The terminals are not something that are easily replaced. I would start by inspecting all the wires.

You did cut (or remove) the 4 wires required for the PFC installation, correct?

 

The 4 wires are cut. I attempted to pull the terminals (by inserting a pin in above the terminal to release the latch tab) but I was unsuccessful. So they ended up cut.

For a while there I thought I found the problem was one of the cut wires grounding out and possibly starving the sensor of power. The car went for a full 20mi drive but then started stalling again. .

I'll be back on the task tomorrow but thank you for the suggestions of where to focus my efforts.

David

 

After wiggling the wires behind the ECU and watching the signal come and go, I focused my efforts there and found that the cut wires in the harness were grounding out. So while the MAP wiring was intact, one of the cut wires must have been messing it up. Knock on wood, I've had no issues since wrapping the wire ends in electrical tape.

David

 

That makes sense, any time you have a wire grounding out you'll get a world of weirdness. Make sure they're well insulated and secured so it doesn't happen again!

Hope this is the end of the thread .

Dale

 

I hope so. I got through two autocrosses this weekend and my biggest problem was the tuning of the driver. I got better as I went though.

 

You made me feel a little better by not being the only one who couldn't get those wires to release. I remember my back finally giving out and I ended up cutting too. Probably over-kill, but I eventually put a tiny daub of silicone on each exposed end and let it set up before using silicone self-fusing tape.
Glad you found the issue.