1998 540 throttle response not instantaneous, too much lag

[Eriklane]

200k miles, well cared for, newer coils and plugs, using premium gas. When I jump on it, there's a definite lag of a second before it grabs. I've checked the cable and it all seems fine. I was wondering about crank pos sensors or possibly if the transmission shift solenoid could be suspect. I do notice in the am when I first drive away that the car seems to hang up a little in first, but other than that, I don't notice anything.

Also was going to check the fuel pressure as maybe the FP regulator is bad. Newer fuel filter also.

[scottieducati]

Ever have your injectors cleaned?


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[R Shaffner]

In my 540-6, I'll get hesitation whenever one or more of the coil packs are going bad. It's worst in a higher gear at lower rpm (like opening the throttle in 3rd at low rpm, while driving around town).

If you have INPA, you can look at the roughness screens to see which cylinders might have weak coil packs or bad injectors. You can swap the coil packs around pretty easily, or buy a few and swap them in (if you don't want to spring for a whole set).

[CPHES]

Simple stuff - motor and trans mounts. Motor mounts can go soft, they don’t have to be broken. Trans mounts are easy to diagnose. Also a failing guibo. They can all cause small parasitic losses that add up

[Eriklane]

guibo?
Was told by prior that coils and plugs and cats and 02 sensors and maf were all done after 2017 and it hasn't been driven that much since. I bought it with 190k 2 yrs ago, has 201k now. I did the fan clutch also. I will check the mounts. I don't have inpa, unfortunately, but have a smartphone app that shows fuel trims and stuff, but haven't dove too deep. Injectors I haven't thought about, that's kind of a pain, but I should ask the prior also on that.

[CPHES]

Guibo - it’s the rubber joint coupling between the transmission and driveshaft - if you have no check engine light, start with examining the driveline stuff.

[Eriklane]

Do you have a name or part?

[scottieducati]

It’s called the giubo, or flex disc. It goes where the driveshaft meets transmission, opposite the CV / rear diff.


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[CPHES]

Where the Trans and Driveshaft meet. Not the Driveshaft to Diff / Not on a BMW anyway. That joint is a CV Joint. Here's the link to FCP https://www.fcpeuro.com/products/bmw...0-26111229065l

You need to know how to install it. getting it aligned incorrectly will lead to it being destroyed.

[scottieducati]

Whoops posted that wrong. Edited.


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[Eriklane]

Thanks, good to know, but I don't suspect that's the issue. No vibe, but I'll check. Seems to me almost to be a fuel issue. When ya jam the accel, it's all about fuel and air, I hope to check the fuel pressure and bleed this week...saw a video where the guy showed pressure good, but it was bleeding off, dropping pressure when shut off. Will try that.

[Eriklane]

I went to check the fuel pressure and couldn't find the port. Is it under the car? Also, I tried putting the car in 2nd and then hammering it, it still lags, so that tells me it's not the downshift mechanism.

[scottieducati]

You test at the fuel rail, there is a schrader valve to connect to. Or at least some have one?? https://www.bimmerfest.com/forums/sh.../572293?page=2

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[Eriklane]

Where, looked all around engine bay.

[pietern740il]

+second the coil going bad

After changing my spark plugs, I started to get rough idle, and poor throttle response. Check engine light was on, but I had figured it was because I removed the secondary air pump. I had three bad coils.

[Eriklane]

How to test coils?

[CPHES]

If the coils are bad, you will see misfire codes. Do you have any codes?

[Mike WW]

I realize there's quite a bit of difference between the 6's and 8's, but I've had a similar problem for a while with my 02 525it. Starting from a stop and flooring it there's a brief pause. My theory, as yet unproven, is a sticky throttle body since it's drive by wire also. Otherwise mine runs fine, no codes, good idle etc. Longshot, but maybe.

[CPHES]

Good to check, but 98 is not drive by wire.

[wagons ho]

I've always been curious why the OP is posting in the wagon sub forum, as a 98 non vanos wagon in the states would be extremely rare, but...
97 98 have no Schrader valve on the fuel rail.
My guess is the same,as others, vacuum leak.
But this delay hopefully is not to be confused with a big kickdown event, when transitioning from 20mph to floored?
If not a wagon, post in main thread, but even there, responders get confused with early cars as most people have m62tu's.

[pietern740il]

Based on Eriklane post

Maybe should start with the transmission, check fluid level. Also would need to understand the lag.
Does it happen only with the engine is cold, when in the highway how does she respond say from 40mph to 60mph.

What brand plugs and coil did you install? Were you having this problem before you change plugs and coils?



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[Mike WW]

Good to check, but 98 is not drive by wire.

Oh well. I thought about that, even checked Realoem and didn't see a cable plus I thought the V8s got it before the 6's. Shows my 540 specific expertise I suppose.

[Eriklane]

No. I do have a pending p0443, but that's evap emissions. And P0171 which is a fuel mix or lean code, but I have sprayed brake cleaner everywhere and found nothing. Neither code is throwing the CEL however. I do notice at startup that it can sometimes be quite rocky, or it will barely run, but it doesn't do that every day.

[CPHES]

Did you ever go thru the driveline loss items Mounts, and CSB?

[Eriklane]

No, haven't...csb?

Because it idles rough sometimes, and has the fuel trim code pending, I suspect something in fuel. I am suspecting the fuel pressure control valve. I wanted to check the fuel pressure but can't find the valve. Is it under the car? Wondering if it's bleeding.