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quad121

E39 M5 Running Rich

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I wonder if anyone can advise on a possible solution to my problem. The car is performing fine but when you coast in gear for say 50 yards whilst you have INPa connected Analogue 2 screen. The lambda integrators drop to 0.75 which throws a fault code up.

I have checked for leaking injectors by only starting the car when left over night to see if there's any black smoke on initial startup but there isn't. Just a little grey smoke.

Thankyou for any ideas for what this could be?

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There could be a couple of causes.

 

Likely i'd start with your MAF's. These cars are notorious for being able to carry poor MAF's yet not trigger a code and they could be reading high.

 

Does the car run poorly also or simply set the code?

 

If it runs poor you can disconnect them and the car should run better and not set that code if they are problematic, that would point to the MAF's. (Although obviously it will set a MAF code)

 

Another possibility would be poor vacuum at the FPR which is there to reduce pressure at idle. Either the hose which it connects to it and to the throttle body under the plenum is perished, or perhaps the diaphragm in the FPR could be split although thats not really that common, the hose is more so.

 

If that happens the pressure is too high at idle (or coasting in your case) and the car overfuels. If you start the car and pull the hose off the FPR you can put your finger over the end of the hose to see if the suction there is good, that way you can rule out the hose or the FPR.

 

There's a good thread over on M5board about replacing it and it may help you visualize where it is. Pay special attention to the elbow connections too which can become brittle and fail

 

http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/160917-diy-fuel-pressure-regulator-throttle-body-vacuum-line-replacement-2.html

Edited by jamiepeers

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Thank you Jamie I should have said that I replaced the MAF's about 3 months ago with Bosch units. Performance is fine and idle is fine with no lumpy tick over.

If there was poor /no pressure at the fpr would this not effect tick over at stand still also?

Edited by quad121

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Also under the plenum what do you think needs replaced. As far as I know the hoses etc have never been changed. I don't want to remove the plenum then find that any rubber parts etc. fall to bits and not being able to use the car as its in constant use

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Although we can probably rule them out it would be good simply to unplug and test, never assume.

 

Are the Bosch units guaranteed genuine? as in from a verified source and not say ebay? Are the units also the proper "029" units not the sometimes used VW "032" units?

 

I only ask as it would be silly to simply disregard based only on a recent purchase if the above can't be verified.

 

As for hoses you are looking at the one shown in the thread link regarding the FPR. The pressure issue you'll have at idle will be too much pressure, not the other way around as the FPR vacuum supply bleeds this off to regulate it at idle, hence too much fuel and a possible rich condition in this state.

 

Hoses under the plenum that could be checked also would be ones from here

 

http://www.realoem.com/bmw/showparts.do?model=DE93&mospid=47592&btnr=13_0838&hg=13&fg=15

 

7 8 11 16 & 17 are the obvious ones but don't discount others

 

Also hoses from this diagram here can be troublesome

 

http://www.realoem.com/bmw/showparts.do?model=DE93&mospid=47592&btnr=11_2671&hg=11&fg=45

 

 

Be aware that the hoses above shown will normally throw the same code although the integrators will max out the other way as the ECU will be seeing a lean condition, not a rich one as you describe

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Hi Jamie

Thanks for your reply. I tried unplugging the MAF's and it seem to slow the response from the engine and when lifting off the throttle it almost stalls.

As to the FPR would this not also effect the engine on tick over as well? As when coasting in gear?

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Yes I t would as in effect the engine is idling, all you are doing is rolling so same symptoms apply.

 

Also a good idea to look at whilst under the plenum would be the ICV as this controls mixture somewhat by its function. If its closed or stuck it could cause a rich condition.

Edited by jamiepeers

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What about the llambdas?

Mine was really rich and stunk of fuel even when hot. Replaced pre cat llambdas and presto she is sweet as with no smell at all even on start and the black soot on the boot isnt there neither.

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I would think something such as that would throw its own accompanying code.

 

The reasons behind an ICV or possible vacuum at FPR/diaphragm diagnosis is these things are not actively monitored by the ECu and will not throw a code themselves, rather a code for something else which is symptomatic of those symptoms such as a rich code on the fuel trim

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Another possibility would be poor vacuum at the FPR which is there to reduce pressure at idle. Either the hose which it connects to it and to the throttle body under the plenum is perished, or perhaps the diaphragm in the FPR could be split although thats not really that common, the hose is more so.

 

If that happens the pressure is too high at idle (or coasting in your case) and the car overfuels. If you start the car and pull the hose off the FPR you can put your finger over the end of the hose to see if the suction there is good, that way you can rule out the hose or the FPR.

 

There's a good thread over on M5board about replacing it and it may help you visualize where it is. Pay special attention to the elbow connections too which can become brittle and fail

 

http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/160917-diy-fuel-pressure-regulator-throttle-body-vacuum-line-replacement-2.html

 

Doing some work on mine today and had the plenum off, I'd remembered reading this a few days ago so had a look at my FPR hose and whilst the main hose was ok, the small piece that goes from the FPR to the 90 degree joint was perished and falling apart, so I replaced it.

 

I would never have known to check otherwise...

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