Juddering when accelerator slightly in use....

[Brianmoooore]

Right, I've had a go at my wife's touring this afternoon.
I checked the airmeter to throttle body hose - all OK
Tested the TPS, both at idle and WOT - definitely OK
Tested the IAT sensor and the airflow meter thoroughly, and compared them with a spare one. Both IATs gave the same readings, and both AFMs gave identical smooth transitions from flap closed to fully open. Couldn't change the AFM assembly over easily, because it, and its mounting bracket are modified for LPG.
Checked the blue temp sensor at the ECU plug, to include the injector plug and the C101 in the test as well - Perfect readings.
Since I had the ECU off, I stuck in a spare 380 ECU in place of the 173 ECU fitted.

Road test - No difference at all. 1500 RPM on petrol and it starts to kangaroo. Change (almost seamlessly) to LPG and it stops jumping immediately; change it back to petrol and its off again.
So now I've eliminated everything except the fuel pump, filter, pressure regulator and injectors.
Had a bright idea, so pulled off the road, pulled the vacuum pipe from the fuel pressure regulator, plugged the hose so as to avoid a vacuum leak, and drove it again on petrol.
This seemed to eliminate the jumping at 1500 RPM, but would still do it if I let the revs drop to 1000RPM.
Vacuum hose I removed refers the atmospheric side of the FPR to the partial vacuum in the inlet manifold under these driving conditions, so reducing the fuel pressure in the fuel rail. Disconnecting it will raise the fuel pressure.
Don't really know if I'm onto anything yet, as I haven't investigated further, but it's food for thought.

[Martinaston]

If it only does it when running on petrol could it be because the LPG burns slower, giving it a smoother power stroke and better idle ? (i'm not sure how lpg works)

[Speedtouch]

Daimlerman, Miller are able to supply custom software to suit your engine spec; it cost me no extra to specify a 7,000rpm rev limit instead of the stock 6,500 one (in fact, they sent me the stock chip with the kit, and are sending the upgrade chip separately free of charge!)

I've yet to fit it - need to get my a*se in gear...

Fitting a new fuel filter to my car recently improved the starting noticeably but there's still a bit of kangarooing at times, though not quite as bad - so maybe it is something to do with fuel pressure.

Brian, what is the 'C101' you refer to?

Cheers!

[Brianmoooore]

C101 is the plug and socket on the bulkhead, near the fusebox, where the engine loom plugs in.
LPG does burn a little slower than petrol, but I can't see this having any significant effect at the revs we are discussing.

[daimlerman]

320iSE,Maurice,Thanks for the Miller info,would you be kind enough to let me know how you get on with the kit,please?I think that this may be the way forward for me.

[Speedtouch]

Will do daimlerman. Might fit it this week if the weather improves a bit...
There's more info in the thread from kam-325i entitled "what do you think......."

[liam012]

so basicly brian rcould you say raising the fuel pressure has helped the problem? or at least moved it to 1000rpm
the rerason i ask is that I have eliminated judder at constant speeds by replcing cps sensor but now i still get it at 1000rpm.
i fear maybe escess play in the diff but not 100$ yet, unless the car is running unusually lean at low revs - to me it feels like the wheels start to turn the engine and the shake really comes from behind me as if the diff is trying to brake loose!
i really hope it isnt the diff....

[Speedtouch]

Alot of '80s fuel-injected cars had this problem at slow traffic speeds. I think it was caused by the manufacturers including fuel cut-off when you backed off the throttle (the idea being to save a little fuel).

Maybe it's just a 'characteristic fault'?

[liam012]

to be honest its too bad to simply be a characteristic fault - it would warrant a recall!

[Speedtouch]

Maybe 80's Yuppies were always in too much of a rush to notice it?

[Demlotcrew]

Found out last night my wife's tourer has joined this club!
Normally runs on LPG, but for other reasons couldn't use that last night, and had to drive on petrol.
As far as I can tell the kangaroo effect only cuts in when the throttle position switch is off idle and not wide open throttle. Also (normally) works perfectly on LPG, so spark and gasket problems can be discounted.
First thoughts, though, not as to why, is that the AFM is not used on LPG, idle or WOT, but is used on part throttle.

AFM is used on idle and off idle upto 80% throttle (WOT) then the ECU uses its enrichment tables for correction on feul/air mixture.

Sounds like it could be a TPS or AFM or both.

But i would say its the TPS as those M40 lumps have them filled up with oil over time.

Andrew

[Brianmoooore]

Found out last night my wife's tourer has joined this club!
Normally runs on LPG, but for other reasons couldn't use that last night, and had to drive on petrol.
As far as I can tell the kangaroo effect only cuts in when the throttle position switch is off idle and not wide open throttle. Also (normally) works perfectly on LPG, so spark and gasket problems can be discounted.
First thoughts, though, not as to why, is that the AFM is not used on LPG, idle or WOT, but is used on part throttle.

AFM is used on idle and off idle upto 80% throttle (WOT) then the ECU uses its enrichment tables for correction on feul/air mixture.

Sounds like it could be a TPS or AFM or both.

But i would say its the TPS as those M40 lumps have them filled up with oil over time.

Andrew

Keep up to date, Andrew! Look further up the thread and you'll see I've eliminated both the TPS and the AFM from the problem, plus a few other things.

[smithy318i]

I have tested my AFM and it seems to be working. I have been unable to check the FPR as i have been too hungover to test it.

However i have been reading that a faulty FPR could mess up the fuel/air mix.

Occasionally, a small leak will develop in the fuel pressure regulator diaphram that allows fuel to enter the vacuum system. This upsets the vacuum system. Check for the presence of fuel in the vacuum line to the fuel pressure regulator. If fuel is present, replace the regulator.

Im going to test mine today.

[Demlotcrew]

Keep up to date, Andrew! Look further up the thread and you'll see I've eliminated both the TPS and the AFM from the problem, plus a few other things.

I was trying to help the thread originator as he doesnt have LPG or access to diagnostic equipment be it a simple miltimeter or a BMW diagnostic node.

Its not like you need any help!

Andrew

[Brianmoooore]

Any help on this one I'll gladly accept!
Interesting point that Smithy318i came up with. Have to look into that one further, although there wasn't any obvious sign of liquid fuel in the pressure reg vacuum line when I pulled it off.

[Demlotcrew]

Brian for you the next step would be to stick a Wideband on the tail pipe take the car for a drive, data log the findings.

From what you are saying at 1500rpm with the vacuum pipe on the FPR the car is running lean, we can work this out because when the vacuum line is removed the pressure in the rail increases and thus would add that little bit extra through the injectors getting close to the magical ratio of fuel/air.

I think you can rule out the fuel pump as if it was the pump i would not expect it to be RPM dependant (ie only at <1500rpm)

The next two are the injectors ECU and FPR. I know you said you swaped the ECU with no effect but there could be loom issues. Front crank pulley sensor?

Theres nothing left!!!!!!!!

Andrew

[Brianmoooore]

Don't have a wideband, but the LPG gear has a standard lambda sensor which displays on a laptop from the LPG ECU diagnostics, even if the car is running on petrol, so I could get some idea of mixture conditions.
The injectors on this car are suspect because they do lead an "unusual" life. 99.9% of the time they just sit there unpowered, but with full fuel pressure applied. This can lead to gumming up of the injectors, I'm reliably informed.
Crank sensor is used both on petrol and LPG, and any spikes in the signal from this, giving extra spurious sparks would lead to massive blowbacks in the inlet manifold, as LPG/air mixture is ignited via an open inlet valve.
One problem I have with this car is getting the chance to work on it. I have 13 and 16 year old daughters constantly demanding a free taxi service, so it's never still for more than a couple of hours!
Recently took about six months before I could get the engine cold enough to set the tappets!

[DaveD]

i had some of this last year ..

i don't suppose that your throttle body gasket needs replacing ...mine did and it cured it...37p!!

[Rob_316i]

Thanks Dave - I have had the throttle body off and the gasket was in 1 piece. Cheers for the suggestion tho - would have been nice if it was that!

[DaveD]

mine was too.............

[march109]

This has been happening to me! see the thread "stupid bloody car"

Its got so bad now that I can't use my car. What a PITA, has anybody got any leads on what this may be yet?

[Speedtouch]

Fitting a MAF in place of the AFM has cured my car's kangarooing; can now drive at idle speed in 5th! Some pics here:

http://uk.pg.photos.yahoo.com/ph/mtjhun ... e2&.src=ph

[Martinaston]

320iSE how do you adjust the CO on that MAF ?

[march109]

looks like MAF it is,

is it hard/costly/time consuming?

How much should I budget to do it and whats involved?

[Martinaston]

march109 i'd confirm what the problem is first before spending money on a MAF conversion. If you have a worn clutch that can cause your symptoms by changing to a MAF meter it might just increase the idle speed and mask the original problem.

[Speedtouch]

No increase in idle speed - it's the normal 700 rpm. There's no facility on the MAF to provide CO adjustment; it's all taken care of by the chip program I guess.

[Speedtouch]

Miller are giving a system away in their New year competition http://www.millerperformancecars.com/rules.html

I took my time over my installation (didn't want to f*ck it up!), also I went a different route on the wiring to retain my car's original loom intact - should I ever need to revert it back to standard.

It's easy enough, just a little fiddly in places - but it's nicely engineered and so far, so good.

[liam012]

brian if you are still following this problem do any of my trhoughts http://www.e30zone.net/modules.php?name ... 466#561466
have any remote link with that judder problem?

[smithy318i]

I plan on replacing my FPR, fuel rail, and injectors at the weekend just to rule them in or out.

I didnt notice any difference in running at 1000 or 1500 @ <20 mph after i unpluged the hose from the FPR to inlet manifold, however I did notice liquid in the vacum hose.

[Martinaston]

If you want to know if the FPR is leaking fuel into the vacuum hose try replacing the pipe with a transparent piece.

[daimlerman]

320iSE,thanks for the photos and information,food for thought.

[Padzer]

Hi,
Me too. When I lift off the throttle in traffic (2nd, 3rd gear usually). Happens when the car is warned up more so than initially.
Padzer

[liam012]

If you want to know if the FPR is leaking fuel into the vacuum hose try replacing the pipe with a transparent piece.

now theres an idea - i did notice a considerable ammount of residue in the inlet last time i had throttle body off -

have my gauge now so off to test fuel system.....

[march109]

damn this is so bad I'm now driving a chavalier, I don't want to go down the lines of replacing fuel rail, and injectors just yet, I'd rather know what the problem is first.

fancy a MAF conversion anyway though!

I suspect I need a new ICV anyway as I've had problems with it recently. So thats next along with looking for anything else which might be amiss.

[daimlerman]

Just ordered my MAF,of course the price has risen now