Rough Idle - Fixed

[RajB]

Hi
This is my first post and a fix at the same time

In brief - the Fix in this case for my 316i M40

The FIX
Fix - Fuel Pressure valve, leaking fuel into vacuum pipe and dumping fuel into throttle body, causing over rich mixture. Resulting in rough Idle.
Vacuum pipe capped off. Instant fix.

Symptoms
Rough Idle 1 min after cold start. Poor Hot Starting. jerky drive at low speeds, engine go into a cycle of 'chugging' then attempt to stall.

What I tried over 4 months - not all related to rough Idle but may assist other members:
Where possible replacement parts were new or known good used OEM parts

Fuel Pump
Fuel Filter
Fuel Pump relay
Fuel lines cleared with compressed air
New Inlet manifold gaskets, 'o' rings, seals
Engine wiring loom continuity checks
Engine wiring loom connectors cleaned and re-seated
Injectors cleaned new seals and re-seated
ECU code reader - showed no errors
ECU connectors cleaned and re-seated
ECU Software updated
New vacuum pipes
New coolant pipes, also noted rear coolent housing (small connector) was completely blocked - worth checking
Idle Valve (tried 4 different valves, none made the issue better, car now runs great with original valve)
Blue temperature sensor for ECU
New Spark Plugs
MAF sensor cleaned
Injector cleaner (made no difference)


Result - Engine Power restored, economy 35+ MPG round town, hot and cold starting - perfect, low speed jerking gone.

Recommendations - from this case, blocking of the Fuel Pressure Valve is worth doing as this quick and cheap check...

See pic for the temporary fix -

[Contours]

The vacuum pipe on the throttle body is capped off on all 316i M40's and there is an obvious vacuum leak that you can actually hear when it isn't. Is it that you had a faulty fuel pressure regulator or maybe I am missing something. Very clean looking manifold you have.

[RajB]

Contours - wow I did not know that. so this leads to another question, the vacuum pipe from the Fuel Pressure Valve (FPV) where does that go ? ..

The FPV on this car is leaking fuel and I am awaiting a replacement.

Thanks for noting the manifold.. I have added a picture of the engine before i dropped it the car - looks great.

[arrisbmw]

good job , lovely clean engine . you obviously learn a lot in the fault finding process.
where is this blocked water pipe you mentioned , need to check mine have you go an image please.
very interesting post sorry just read temp repair . on fpr
you said soft ware up date on e,c,u how does that work . ?? be interested to know .

( dont know how you cleaned the M.A.F sensor as it hasn,t got one A.F.M works in a completely different way )

and that vacuum on the fpr you blocked off is there for a reason ,
the fpr has a diaphragm inside and yours must be split letting fuel thru. better option would be to fit a new one

Fuel Pressure Regulator
To keep the injectors squirting as they should, a constant pressure needs to be maintained which is above the pressure inside the engine. If the pressure was lower, then fuel would be blown back down the pipes to the tank when the injectors opened, so the Fuel Pressure Regulator (FPR) self-regulates the fuel pressure in comparison to the manifold.

The FPR is mounted to the end of the fuel rail, closest to the radiator. It has a small rubber tube connecting it to the top of the intake manifold, and also connects to the returning fuel hose. It is a simple diaphragm valve, sucked and blown by the intake manifold pressure to open or close the fuel flow. Failure of this diaphragm can result in rich running, lumpy idles, poor fuel economy and even engine failure. Despite this, the FPR does not have a reputation for unreliability.
but I must add wish my engine was that clean . do you go to any shows ?

[ocde30]

Lovely engine. Not too bling - just right.

[Contours]

There is a vacuum pipe from the Fuel pressure regulator to the pipe on the throttle body that you have blocked off there with a fuel hose. The vacuum pipe that is blocked off from factory is on the opposite side of the throttle body -- maybe this is blocked off already.

[RajB]

Hi,

Answers to the questions:
Arrisbmw -

FPR, - when i was checking the vacuum pipes, i remove the FPR pipe from the throttle body, and noted that fuel was in the pipe. a quick flick/turn of the engine and fuel was pulsing out of the vacuum pipe. There the diaphragm would look like it has failed.

MAF / AFM - i am no expert on the difference, however, i did take most of this apart and cleaned the sensor and 'trap door' mechanism with carb cleaner. (it also had some dead spiders in there too)

Shows - yes but only locally as the car have not running well enough to go far... hopefully with the FRP replacement is in place this will change.

Software update was carried out using the following: Using a friends laptop + app with a special connector in the Diagnosis Port to USB connector on laptop. Software app is specific to BMW. ECU software was updated with prompt to update yes/no on connection. Software and connector (same connector as e36) £120

Pic shows the software update in progress

Blocked pipe - on the back of the cylinder head, under the Idle Valve i this water housing - the smaller of the two connects to the inlet manifold - on this car housing was not only corroded, but the smaller pipe was also totally blocked with what looked like dried sand..no coolent could pass. I replaced the housing for £9 (OEM) unit from eBay





Thanks for the comments for the engine paint job...took many weekends to strip parts, clean, grind n paint and refit..

[RajB]

All - swapped out the old FPR for a new unit yesterday - confirmed the old unit defective - - All OK now
( i am going to cut it open just see where is failed)

[TurtleDesignTech]

Great looking engine.

To restore the silver parts (intake manifold, etc.) did you have them painted or are they just sand blasted back to bare aluminium?

[Foe]

Excellent work. I love an update
Very clean engine too!

[arrisbmw]

thanks for all that info . did you find the s/w updt improved anything.


thanks

[RajB]

Hi - I painted the aluminium part with aerosol based brake caliper paint (a lot a cleaning, Gunk de-greaser and wire brushing)

As for the software upgrade - I have not noticed any difference over the past 80miles and will report back if I see anything

or anyone on this forum has performed a software update and noticed any changes?

[TurtleDesignTech]

I am a bit surprised that there is even such thing as a "software update" for this ECU. I thought you had to flash thee EEPROM chip directly.

The chip itself and ECU are not particularly sophisticated as far as I understand. Pretty much a basic Input --> output system with some fuel and air maps.

Best person to talk to is "Speedtouch" on the forum here, who has been selling chips and making custom maps on them for years.

I am a bit surprised you manage to get 35+ MPG. Didn't know it was possible with these old single cam 1.6 engines.
I have done a full maintenance sweep similar to yourself and still only get 33MPG max on a good long run (31 MPG average).

@arrisbmw What MPG do you get?

I hope I am missing something, as a few more MPG would be great.