1998 RT C200V fuel pump replacement?

[KaptainK]

Yesterday discovered I’m only getting 1.6v reference on the IAT power wire. Should be around 5v. Might be why I’m getting high air temp reading when cold. At any rate, it’s been running fine for three days now. About eight short trips, with no problems.

[booster]

Originally Posted by KaptainK

Yesterday discovered I’m only getting 1.6v reference on the IAT power wire. Should be around 5v. Might be why I’m getting high air temp reading when cold. At any rate, it’s been running fine for three days now. About eight short trips, with no problems.

I may have misunderstood your previous post where you said you were getting 50-50 run good run poorly. I assumed this was after the disconnecting of the O2 sensor. If it was after the disconnect, what changed that would have made it run well and consistently now?


It would certainly be prudent to find out is any other sensors are getting low voltage to them. IIRC there may be multiple points they pull the 5v from on pcm, but I am sure that could vary between models.

[KaptainK]

It ran fine for about a month when I first bought it. It actually started acting up the same day I filled the tank up, after running it down to fumes. I kept thinking, fuel pump, dirty in tank filter, pump sock clogged, etc. it just acted like it wasn’t getting fuel. I did worry about that tank of fuel also, so I put in a couple bottles of heat, thinking it may be water in the fuel. Fuel pump checked out OK with a pressure gauge test. I didn’t test the fuel for alcohol or water. Nor did I drain and clean the tank, but I did burn half of the fuel off and filled up with premium, hoping to dilute the problem away, if there was bad gas. I have also been checking grounds and wiggling wires all over, as well as purchasing the OBD tool and Fusion OBD. I have discovered that I have several issues. Right now, I’m just trying to figure out what’s going on. It’s running fine at the moment, despite the O2 sensor wires being cut, and despite the IAT sensor reading 200+ degrees.I don’t think that’s been the issue.
* And of course I changed the external fuel filter.

[TX-Trek]

This is where a wiring diagram can be your friend. It will show the various circuits, connector pin ID, reference voltages and CAN/LIN BUS circuits on newer vehicles.
With a diagram you can verify if it is actually 5v reference required and what other sensors may be on that same 5v reference circuit. Wiring diagram will typically show any reference voltages at the ECU pinout.
Let's say in this case 5v is required and there are no other sensors on that circuit and all power and grounds are ok. Remember that a poor ground, corroded connection, bad wire can cause voltage drop. By going directly to the ECU pin connector, it can be back-probed to verify that 5v is being supplied as required. If the 5v is there, and if you only see 1.6v as reference with sensor unplugged, that immediately tells you there's a problem in the wire/connectors (if any) between the ECU and the sensor. If the ECU is only providing 1.6v instead of 5v then the trouble is within the ECU OR there may be a grounding issue with the ECU. Always check grounds.
Makes it easier to start hunting for an issue.
If there are other sensors on that same circuit and they show 5v, then that helps narrows it down to the wiring between the IAT and the next point in the harness.
I use MitchellDIY on our RT, factory CD manual from ebay for our Silverado and WIS/EPC CD for our german car. I'm not affiliated with any of them, just pointing out different available sources for factory manuals, as well as the original printed shop manuals if still around. I like the Mitchell online anytime access, its about $45 I think for 3 years of access. I've used it many times as a reference and to verify wiring.

[KaptainK]

Thanks! That’s exactly where I am headed. I found a diagram which shows IAT sensor voltage on pin number 22, on the red PCM connector. I will get there, this is a bit deeper than I’m used to going. Last week I was painting cabinets. The week before that I was cutting and installing new insulation and wall panels. Before that was the 12 V system in the coach. Water pump and plumbing prior to that. New AC and rear hatch just before that! Exhaust, solid brake lines, water leaks. I’ve been all over this thing and don’t trust it to get me to the campground yet. But I am making tons of progress!
And I even forgot all about swapping the front seats, relocating the battery, pulling the generator, and gutting the van. Oops, new battery isolator, carpet, new bedroom ceiling, waterproofing, new led lighting inside, led markers and wiring outside...crap no wonder my beer bill has been so extreme lately.

[booster]

I can't say for your pcm, but lots them do not switch the 5v power to the sensors at the pcm, they switch the ground from those sensors in the pcm to the pcm ground or read a voltage drop. That can make for some funny voltage readings at the sensor when it is actively controlling.


If it is a single wire sensor, which are getting kind or rare, but there are a few on my 1996 Buick, those would be standard type using the chassis for ground. My water temp is that way as I just disconnected it as I pulled the engine.

[KaptainK]

Well, my 02 sensors have 4 wires. My IAT has 2. The ground wire shows 12v potential. The MAP power wire shows 12v. Maybe the IAT doesn’t need a 5v reference...that’s just what the Internet said...still running fine today!

[booster]

Originally Posted by KaptainK

Well, my 02 sensors have 4 wires. My IAT has 2. The ground wire shows 12v potential. The MAP power wire shows 12v. Maybe the IAT doesn’t need a 5v reference...that’s just what the Internet said...still running fine today!

One the four wire O2 sensors, two of the wires are for the internal heater, so those would be 12v in and out. The other two are the signal wire which is self generated in an O2 sensor so no voltage input to it, just a plus and a minus out with about .5v running at stoick and a range of something like .1 to .9v. The other sensors need the power input to them to be able to give a signal out.

[KaptainK]

Just an update. She has been running just fine for about a week now. It’s a miracle. I’m hoping it was just bad gas. I’ve never had anything like this happen before, if that’s the case. Fingers crossed. Thanks for all the input.

[Scottie409]

There is no extra tap on the fuel pump on Roadtrek however there is a pickup tube in the fuel tank that feeds the onan electric fuel pump. This should have no effect on the vehicles running.