97 318is engine cut out around 2700 rpm and then again at 4000 rpm

[polygaryd]

You are correct that the "spike" was on tps signal wire when testing voltage from closed to open. what I'm saying though is its not a spike as in it reads out of of normal as a high then goes back to normal voltages as you move along the throttle curve. It was just simply and observation that the throttle body feels much more resistance pressure wise while moving from closed to open and the voltage was recorded at the point where it goes from easy to harder to press the throttle open. It probably means nothing as the voltage doesn't jump or anything, but I thought it may mean something to you that I am not aware of.

I know what you mean about notes. I have a whole sheet of connectors, pins, voltages with this or that connector connected or not for various tests, what pins go to what wires, what other sensors connect to those wires/pins. If I knew it was going to be such a pita I woulda sold the car off for parts but now that I'm into it for a lot of hours I feel like I have to make it work or all this is for nothing.

[polygaryd]

So today has been interesting, I pulled up all the wiring for the fuel tank pressure sensor and haven't found anything at all wrong with any of it. I found the sensor itself and unplugged it, plugged everything else back in, tested the voltage at tps pin 1 and I get my 5v, I plug back in the tps sensor and I STILL GET 5v on tps pin 1???

I have all connectors connected and I can communicate with the dme with a scan tool and I get my 5v on tps pin 1. I couldn't do both at once before today, meaning I couldn't have the x6031 plugged in if I wanted my 5v on tps pin 1 but then couldn't communicate with the dme OR I could have x6031 plugged in and communicate with dme but couldn't get 5v on tps pin 1. After simply unplugging the fuel pressure sensor and plugging it back in everything is fine.

I also fixed the wiring that goes across the trunk area to be held in with the clips from the black plastic molding trim piece but that's it. I didn't see any wires with sheathing broken or wires touching anything, etc. I'm stumped. I have a theory that the fuel sensor will kick on again at some point to report to the dme and cause the shortage of voltage on tps pin 1 but I have to drive it to test that theory. If the voltage drops on the tps pin 1 again I'm going to unplug the fuel pressure sensor and see if it comes back to normal, if so I'll get a new fuel tank pressure sensor and test again.

[bmwdirtracer]

I think you've found the culprit (the fuel tank pressure sensor). Now, while you have 5 volts at the TPS feed, check the voltages of the sweep on the signal line, engine off. ignition on, TPS connected.

[polygaryd]

how do i still get 5 volts at tps line when i plug back in the fuel tank pressure sensor? It's like just by unplugging the fuel tank pressure sensor I reset the sensor and now when its plugged in its fine, I don't get it. does it not get 5v all the time like any other sensor? If so shouldn't it mess up the tps power feed voltage as soon as i plug back in the fuel pressure sensor?

[bmwdirtracer]

Maybe there's an intermittent short in the wiring; or maybe the sensor itself shorts when the EVAP system pressurizes the tank....let's make sure that we've got the "What" first, before we go looking for the "Why". You've had 2 issues: undervoltage on the feed, and overvoltage on the signal. Test the signal voltage and sweep voltage of the TPS again, all hooked up, but with Fuel Pressure Sensor unhooked; key on, engine off. (Fingers crossed)

[polygaryd]

I did two tests and voltage sweep is still 0.556v(closed) to 4.04v(wot) with and without the fuel sensor plugged in. The signal line dropped from 5.78v to 5.5v also. after unplugging and plugging back in the fuel tank pressure sensor a few days ago. Ive been driving the car to see if its going to happen while the computer is trying to get all the monitoring tests done for emissions, or if I'll make it a whole tank full of gas and then it will happen when I fuel up again. I was going to try to remove the signal pin from the dme connector and see which side gets voltage like you said that way I dont have to cut the wire..

[bmwdirtracer]

I need to check two things: (1) You say above that "The signal line dropped from 5.78 v to 5.5v also." Do you mean the feed line?
and (2) If you're still seeing 5.5 volts, and not, say, 5.05 volts, there is still a problem (even if this is, indeed, on the feed wire.)

Do you have another multimeter? Or, maybe I should ask, "How sure are you about the precision of your meter?"

The voltage sweep that you're seeing when moving the TPS IS on the signal wire, right?

The pin you'll be wanting to remove from the X6031 is the feed wire for the tank pressure sensor, not the "signal" wire. The side which gets voltage does not matter; what matters is that the voltage doesn't pass through that connector.

There are special de-pinning tools for those connectors, but you'll likely have to make your own, if that's how you want to do the disconnect. I have made these before, for the very similar X20 connector. Basically, you use a telescoping antenna, or the extending part from a "mirror on a stick", and you very carefully cut the piece from it which will precisely fit into the hole, around the pin, but inside the black plastic. Not easy, because the fit has to be exact. There can be no burrs or roughness on the cut, either, so you'll need a tiny round file to smooth the edges after you carefully cut the right piece.. I have yet to find a de-pinning tool set with the exactly correct fit for these BMW connectors.

[polygaryd]

I mean 5.5v on signal pin 2 when unplugged from tps. 4.99v on pin 1 of tps plugged in or not. My multimeter is very accurate. i can check with another one but I'm sure its spot on. The sweep IS on the signal line pin 2 of tps while plugged into tps.

As far as de pinning wires, I was referring to when you had said to "cut pin 44 from x6002 dme connector and see which side gets power. Which ever side gets power is where the issues is, if dme side gets power dme is toast"

i can make a tool for the x6031 connector to de pin wires but im not sure why you want me to de-pin pin 6 (power feed to the ftps) my voltage to tps pin 1 is good for now, I'm waiting for the computer to poll the sensor for data and see if it messes up OR if I will have to cause it to re-pressurize the tank after I fill it again. The tps pin 2 signal line voltage I would think is a separate issue since I can unplug the ftps and tps pin 2 signal voltage is still high?

[bmwdirtracer]

Okay, now I've got it.

If the sweep voltage of the signal wire reads correctly,(connected) which it certainly appears to, and the FEED voltage is now correct, I think it's safe enough to ignore the voltage readings from the signal wire of the DME when the sensor's unplugged.

However, while I'm very glad that everything seems to be working just perfectly, after unhooking and reconnecting the FTPS / X6031, it would seem likely to me that the issue may recur....if only because we haven't actually changed anything, have we?

Realistically, though, if it's all working correctly now, then you'd probably do best by just leaving it alone unless and until the fault recurs.

[polygaryd]

I havent changed anything except one minor thing which is putting the wiring that goes across the trunk area in that plastic trim piece's clips. I totally expect that once the computer polls/pulses the ftps for data that the tps voltage will drop on pin 1 again. If the ftps doesnt fault when the computer runs all its tests for smog (my code reader will tell me when all tests are complete), I will fill it with gas again and see if the sensor malfunctions then.

I believe what happened the last time was filling the tank messed the ftps up. It ran great after the dme swap till I put a full tank of gas in the car and 30 minutes later so the car was back to its normal malfunctioning self. It didnt really occur to me that something like filling you rtank could be an issue because I was unaware of how the tps and ftps were tied together till about a week later.

I just want to recreate the issue by either driving the car a lot and seeing which way causes the issue again, then replace the expensive sensor and test again by driving another 300 some odd miles to see if it reoccurs. I will definitely post back, as for now the car is running great again and I really didn't do anything but put the trunk wiring in the clips in the trim piece and unplug the ftps and plug it back in...

[bmwdirtracer]

I'll be keeping my fingers crossed for you, hoping that the problem has mysteriously cured itself. (I have had quite a few BMW's do that for me, over time, on different issues)

HOLY CRAP! That thing IS expensive!
https://www.fcpeuro.com/BMW-parts/31...ssure%20sensor

[polygaryd]

What I don't understand is why the issue seemingly went away only when I unplugged the ftps and plugged it back in at the sensor itself. When I would unplug the x6031 it would bring the tps 1 line back up to 5v BUT would drop it back down as soon as I plugged back in the x6031 yet is now staying at 5v on tps pin 1 when I unplug the ftps at the sensor itself and plug it back in. Why wouldn't disconnecting the x6031 "reset" the ftps like unplugging it at the sensor itself has done? A break in power and ground should be a break in power ground no matter where you do it in the line in theory. Thoughts?

[polygaryd]

The my code reader says all the monitoring tests have completed and it has 0 codes meaning the ftps has to have communicated with the dme and NOT caused an issue with the tps. So its ready for emissions and would pass right now. Next test is to put fuel in it and see if the ftps freaks out now that the dme has completed all its tests.

[bmwdirtracer]

Quick, go get your inspection!

[polygaryd]

well after the computer went through all its tests and was ready for smog testing, I put some gas in it and drove about 75 miles more, nothing happened, so I filled the tank thinking it might create more pressure for the sensor, but nothing happened. So after 250 miles of driving and the car is still fine. I'm betting the sensor will fail in the near future though.

[bmwdirtracer]

Did you pass inspection????

[polygaryd]

I didn't need to do smog a this time it had passed before this happened. I was just using the fact that the dme ran through all its tests for smog and passed the checks meaning the dme did communicate with the ftps and didn't cause an issue. If I did need to pass smog it would with no issues.

[bmwdirtracer]

Oh good....I'll keep my fingers crossed for you that the problem has gone away forever!

[polygaryd]

I hope it has gone away forever, but if not I know what the issue is and can remedy it very quickly. Thank you for all the help.