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///M3 Forum
The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 11-29-2016, 04:10 PM   #1
topher339
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Bad TPS?

So, I was driving back to Arizona on Monday after Thanksgiving break and passed through Flagstaff. It was below 30 degrees and snowing hard. I was moving from a stop and trying to catch up to traffic speed (had to pull over to the side of the freeway for a few minutes) when I lost traction for a second and the DSC triggered. After that, I had a very noticeable drop in power and couldn't seem to rev much over 4k rpm. I thought maybe it was just to keep me from losing traction again. I made it to my destination and all seemed fine.

Fast forward to today and now whenever I try to go over 4k rpm, the car starts bucking and jerking. When I go back to lower rpms I'm only getting what feels to be half power. Everything seems to be pointing to a TPS problem but after looking around it sounds like a few people have had similar symptoms with bad fuel pumps. No new lights have come up. My SES has been on for a while (bad cats) so I'll try to pull some codes when I get back from school tonight. I've also heard that some have had success with using MAF cleaner the clean the sensor (the one in front of the engine) and get it working again.

What do you all think?
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Old 11-29-2016, 04:24 PM   #2
M_3_X
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As far as I know, The TPS would give you an EML light, not an SES light.
It sounds like a fuel issue, i would test/fuel pump/check fuel pressures first.
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Old 11-29-2016, 04:29 PM   #3
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OK. I was really hoping it wouldn't be fuel related but oh well. I imagine there's a thread or two around here to tell me how to test pump and pressure?
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Old 11-29-2016, 04:34 PM   #4
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But also make sure you don't have any new codes that could point somewhere else...
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2002 ///M3 Coupe, Steel Gray, black leather, HK, 6MT.(01/2015-current)
2005 X3 3.0i ZPP, Htd seats, Htd strng whl, Black Sapphire on Terracotta.(08/2008-current)
1991 325i Convertible, 5MT, htd seats
2004 330Xi Orient Blue, 6MT, Sport, Premium - Son
1995 ///M3 Coupe, Luxury, MT, Htd seats, Cosmos Black.(11/2011-01/2015)
2003 325Cic Orient Blue, Premium (03/2007- 03/2010)
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Old 11-29-2016, 04:44 PM   #5
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Will do. I'm going to try to get it home so I can use my reader.
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Old 11-29-2016, 05:32 PM   #6
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Just tried pulling some codes. The only ones I got are for the bad cats. No new ones.
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Old 11-29-2016, 08:43 PM   #7
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I'll grab a fuel pressure gauge and test the pump, hopefully, tomorrow.
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Old 12-01-2016, 05:45 AM   #8
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Quick test on the front TPS is to check it with an Ohm reader. As the throttle opens the resistance should increase steadily with no sudden spikes up or down.
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Old 12-01-2016, 05:40 PM   #9
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Just finished testing the pump pressure. Results are:

Fully Primed - 65psi
Running (5k rpm) - 68psi
Running (idle) - 62-63psi

I never got a reading above 68psi. According to the Bentely manual and jfoj's write-up (http://forum.e46fanatics.com/showthread.php?t=929501) I should be getting around 72.5 +/- 2.9 PSI. It looks to me that the pump is soft failing. Anyone concur?
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Old 12-01-2016, 05:41 PM   #10
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Quote:
Originally Posted by Bates1 View Post
Quick test on the front TPS is to check it with an Ohm reader.
Ok. I'll see if I can find a write-up for that. Thanks.
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Old 12-01-2016, 10:31 PM   #11
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Quote:
Originally Posted by topher339 View Post
Just finished testing the pump pressure. Results are:

Fully Primed - 65psi
Running (5k rpm) - 68psi
Running (idle) - 62-63psi

I never got a reading above 68psi. According to the Bentely manual and jfoj's write-up (http://forum.e46fanatics.com/showthread.php?t=929501) I should be getting around 72.5 +/- 2.9 PSI. It looks to me that the pump is soft failing. Anyone concur?
Try measuring the pressure with the manifold vacuum line removed.
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Old 12-01-2016, 10:41 PM   #12
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How much of a difference could that make? I already put the panels back on and let the car down so I'm hesitant to do it all over again.
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Old 12-01-2016, 11:03 PM   #13
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How much difference will it make? About as much difference as there is depression in the inlet manifold.
The F.P. regulator is trying to keep the design fuel pressure across the injector. The line pressure changes as the pressure on the tip of the injector changes. This simplifies calculationg the injector durations and keeps the patterns consistent.
When the car and throttle are stationary, the highest inlet manifold depression is at idle. Hence the difference at 5000 RPM, but there is still depression at 5000, especially with no load.

Removing the vacuum line will show pressure relative to the ambient atmospheric pressure. This should be as JFOJ mentiond 5 Bar.
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Old 12-02-2016, 12:29 AM   #14
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So I guess if the vacuum line was removed it could possibly show the correct reading? Guess it's back to getting under the car.
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Old 12-02-2016, 07:15 AM   #15
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Removing the vacuum line simulates WOT.
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Old 12-03-2016, 06:32 AM   #16
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In the interest of time, I'm going to go ahead and order a fuel pump (kinda need to be able to get to school). In the meantime, I'll do more testing.
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Old 12-03-2016, 01:34 PM   #17
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Not a terrible idea. Chalk it up to PM.
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Old 12-06-2016, 09:14 PM   #18
topher339
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Is there any chance that one or both of my bad cats got clogged and are causing this? From what I've read, clogged cats can cause a loss of power throughout the power band and an inability to rev past a certain RPM. It can also cause bucking during acceleration. This is exactly what's happening to me and my cats have been bad since May.
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Old 12-12-2016, 09:50 PM   #19
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Update: I replaced the pump with a 255lph Walbro. It seems to have fixed the problem. Power is back and there's no more bucking on acceleration or bogging down. She still seems a bit sluggish but that's probably just me. Appreciate all the help.

Last edited by topher339; 12-12-2016 at 09:50 PM.
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