Your Thoughts Welcome ..... Engine Revs Playing-up

[bob12]

Shortly after the 1990 745 (B200F LH2.4 with cold start injector) got its MOT a month ago it has started to play-up!!

Basically it starts OK but, then shortly after the engine idle revs (800/900) fall off and the engine will stall if the accelerator pedal is not used to keep the revs up. It's not easy to do stationary or coming to a stop as the revs seems to race away uncontrollably. All a bit of a pain!! Once driving the car responds just fine.

The code showing is 2-3-1. i.e. Self adjusting Lambda-sond not operating. Faults C1 (air leaks intake system with itemised checks to be done) and/or D1-6 (all associated with the fuel pump/pressure regulator and fuel lines).

I suspect that non-regular use is part of the cause as the V70 is now the car of choice! The fuel pump is OK.

At just under 150K from new I have never given much thought to the injection etc systems. I have to be frank the area of the throtttle body (TB) was looking rather rough/gummed up even from the outside at the intake pipe from the MAF at the TB. My principle has always been if it ain't broke don't fix it!! The plugs and leads/dissy/ rotor/ etc are all looking in need of some tlc as well having been in for some considerable years .... maybe the rotor and dissy 20!!

I am in the process of stripping out the lot and cleaning everything up having removed the TB today (not a pretty sight!). As the TB is off I shall then move on to the PCV system and all pipe work before turning my attention to refurbishing the other side of the ignition system on the engine.

However, today on removing the TB I was surprised to find a small puddle of petrol in the lowest point of the inlet manifold casting just inside where the TB is bolted. Ooooh, that's not good I thought! The car was last driven a couple of miles about 24 hours before.

Although I haven't considered the matter further or tested the fuel pressure regulator on the end of the fuel rail it looks like the rubber air pipe goes into the manifold near the TB intake. I am wondering if the fuel pressure regulator has finally given up/perforated and is the source of the petrol?

I have not yet considered the Idle Air Valve but that will be released to get to the plastic crankcase ventilation oil separator. I seem to recall there are tests that can be done out of the car to check it is opening and closing.

I would welcome any thoughts that might help me sort this 'little' niggle out.

Cheers, Bob

[Laird Scooby]

I think this is your problem Bob :



Fix the vacuum leaks caused by that frayed vacuum hose and pull fuse #1 for at least 30 seconds and refit then take for a test drive.

Cold start will be ok as the pressure will be increased due to no manifold vacuum (before the engine is running) and then kept running by the IACV keeping the revs up for a cold engine.

Then the Lambda sensor warms up and starts working and the ECU switches to closed loop operation (where it uses the input from the Lambda sensor to keep the mixture and idle speed correct) but it is hampered by an air leak into the inlet manifold (circled on the pic above) and the fact the reduced vacuum reaching the FPR increases the injection pressure.

The ECU "sees" a richer mixture and higher than expected idle speed as a result of the leak and closes the IACV and reduces injection time to compensate. When this does nothing it assumes the Lambda sensor is lying and throws a Lambda fault.
Meanwhile it runs like a bag of cowshed confetti, giving exactly the symptoms you describe.

[bob12]

Originally Posted by Laird Scooby

I think this is your problem Bob :

Fix the vacuum leaks caused by that frayed vacuum hose and pull fuse #1 for at least 30 seconds and refit then take for a test drive.

Cold start will be ok as the pressure will be increased due to no manifold vacuum (before the engine is running) and then kept running by the IACV keeping the revs up for a cold engine.

Then the Lambda sensor warms up and starts working and the ECU switches to closed loop operation (where it uses the input from the Lambda sensor to keep the mixture and idle speed correct) but it is hampered by an air leak into the inlet manifold (circled on the pic above) and the fact the reduced vacuum reaching the FPR increases the injection pressure.

The ECU "sees" a richer mixture and higher than expected idle speed as a result of the leak and closes the IACV and reduces injection time to compensate. When this does nothing it assumes the Lambda sensor is lying and throws a Lambda fault.

Meanwhile it runs like a bag of cowshed confetti, giving exactly the symptoms you describe.

Thanks so much for all that Dave.

I have a spare piece of good hose pipe for the short loop from the FPR to the manifold .... somewhere!!

As I am now down and dirty firstly, I shall clean all things up to an 'acceptable standard' .... everywhere/stuff both sides and replace all consumables (new stocks in hand for years!!).

I was staggered when I looked at the price of a new fuel pressure regulator on the end of the fuel rail. Best price new on the internet seems to be Brookhouse without further searches or even Volvo.

I will give the IACV just a clean up at the electrical connector rather than removing it for testing but, will remove the oil separator plus flame trap (if there) and wash it out as most paraphernalia cleared out of the way to allow easy access. A once in my lifetime opportunity which only occurs every 150K!

Will update shortly'ish ....

Cheers, Bob

[Laird Scooby]

Originally Posted by bob12

I was stagged when I looked at the price of a new fuel pressure regulator on the end of the fuel rail. Best price new on the internet seems to be Brookhouse without further searches or even Volvo. If needed I think I may have one/length lurking about somewhere!!


Will update shortly'ish ....

Cheers, Bob

Here you are Bob, £21 + S&H and (maybe) Import VAT :

https://www.rockauto.com/en/catalog/...regulator,6124

First one on the list, the "Economy" one. Mine took about a week to get here for the 760 (~£30 all in Vs £300+++ in the UK from a Porsche specialist of all people!) but that was a different regulator with two fuel rail legs (one for each bank) so was something of a rarity to find.

Before you worry that it's for a B230, both the B200 and B230 n/asp used the same FPR, the USA didn't get the B200 (too low powered, especially once the extra emissions kit was installed! ) and if you click on the "Info" button on that listing, it gives a whole list of OE and Bosch numbers that it cross references to.

[bob12]

Thanks Dave .... I just put the apparent high cost up to tempt you as I knew you would know where to find a bargain!!

You remember that cheap lot of air filters from years ago only 1 left!!!

Bob

[Laird Scooby]

Email sent about the air filters!

[baggy798]

Sounds like you've neglected and been very cruel to it, I'm calling the RSPCV!! 😡

Needs a thorough stage 0!

Buy some 4mm silicone vacuum hose and replace that fpr hose, the two hoses off the throttle body in that pic, and any others you find.

If you want to replace the FPR, get a used bosch one from a 940, turbo one doesn't matter, LH2.4 will adapt.

Not that these affect your issue but when was the oil last changed? Air filter? Fuel filter? Spark plugs? How is the brake booster hose? Dry rotted?

[bob12]

It's not as bad as it looks Baggy. The hoses are still ok. The fpr one may look dodgy but that was a fix I did some years ago and the insulating tape has gone a bit sticky at the connections which are also secured with j/clips rather than just pushed on. To put your mind at rest the oil has been changed every year together with oil + air filters and plugs nothwithstanding low anual mileage. The fuel filter was replaced about 4 years ago.

This year for it's MOT it was treated to a brand new pair of tail light clusters .... rather smart!

Cheers, Bob

[bob12]

.... and this afternoon spent a couple of hours cleaning the throttle body and trunking to the maf. TB looks like new!

Bob

[bob12]

Quick additional question to the experts (searched the internet but not much luck so far) ....

...... what's the size (internal diameter) of the small length of flexi hose between the end of the Bosch LH2.4 fuel rail between the FPR and the length of metal pipe on the return fuel line as highlighted in the attached pic?

It will be the same size as that on the other end which disappears back to the fuel tank.

I have a spare FPR (somewhere) and I am thinking of trialing/replacing the original FPR if I suspect a 'petrol' problem with it but, I will have to destroy the existing 'flexi' which over 33 years has set hard like concrete!

It is larger than the hose betwen the FPR and the manifold. Rubber or Silicone?

Cheers, Bob