Fuel Pressure Regulator - PeachParts Mercedes-Benz Forum

pentoman · #1 06-18-2008, 08:10 AM

My fuel pressure regulator is not noticeably leaking through the vent hose (the one that looks like a vacuum hose). However is it still possible it's causing me a problem? Does anyone know the test steps for it?

mbdoc · #2 06-18-2008, 08:37 AM

Fuel pressure retention & fuel pressure are jobs that it does.

You need to have a gauge connected to check both.

pentoman · #3 06-20-2008, 04:19 AM

Fuel pressure retention I think is fine because after not using the car for 11 days I turned the key straight to the starting position and it fired immediately. But it did then need one or two seconds of turning over to obtain idle, which frankly it always needs anyway. Once idling it's always steady at 1000 rpm but is lumpy like a Subaru flat-four cylinder.

To get more involved: The problem with the car which is a 190E 2.5-16 is a flatness/lack of response in the low-midrange. Throttle response is laggy and surges. Fuel consumption is average (~320 miles a tank). I tried playing with the EHA adjustment and low down performance improved a lot the more I leaned it out, I was so happy with the car at this point. Top end performance may have tailed off. Then for safety I checked the mixture - at idle it was fine, but at 3000 revs was very lean. Inspecting the number 1 plug also showed a lean colour. So I reset the EHA adjustment and the flat performance has come back. But at least the mixture isn't going to ruin the engine any more.

What gives? I think it must be fuel pressure related because of the difference the EHA adjustment makes.

pentoman · #4 06-22-2008, 03:34 AM

Correction - the fuel pressure regulator does seem to leak. 5 or 6 drips came out from the little clear pipe coming out the regulator when I disconnected it. I assume it's gas from the regulator. Is this amount normal or do I definitely have a bad diaphragm?

On a side note I bought a used EHA from a scrappy yesterday - £2! Mine was potentially leaky. I took it off a 300E with 170k. Fitted but the problem is still present so I'm persevering.

Don't suppose a fuel pressure regulator from a 300E will work on my 2.5-16?

I would imagine not because the fuel pressure specification is different for a M102 8v and M102 16v.

pentoman · #5 06-23-2008, 09:49 AM

Bump!

I'm jolly excited this may be my problem. 2 years living with the oddly hesitant throttle, plus much effort, reading, posting and a top end rebuild. I'd like to now discover that this is the problem so I can get on and replace it! Or if it's not too pricey I'll replace it anyway. It's odd that it's not often mentioned in Jetronic technical documents nor does it get much of a mention in the M102 engine manuals (that I've seen).

pentoman · #6 06-26-2008, 03:47 AM

Well from excitement to pain - I rang the dealer for the Fuel Pressure Regulator price - £263 which is over $500

. The part numbers for different engines are different and this must be 16v specific.

I suppose I should determine for certain if this is the problem then. I've not seen any fuel leak out of the clear vacuum pipe since that one time - perhaps a one off?
The AFM boot (lower half of the AFM) is a more reasonable £30. I might take the AFM and distributor off to look for cracks in the rubber boot. Hopefully AFM and distributor can come off together. But i might separate them to see if the plunger moves freely. Does anyone know how to check test this or what to look out for?

Also I'm not sure if a cracked AFM boot would give a lumpy idle? Nor the fuel pressure regulator for that matter.

190dee · #7 06-13-2014, 05:48 AM

Did you ever sort this problem out? I notice a leak at the small rubber hose on the back of the fuel pressure regulator. The problems I have is that the engine stalls very intermittent.

If I understand it right there should not be any leaks at the rubber hose since it's just a precaution to lead fuel from the regulator back to the intake if the diaphragm breaks. And a faulty regulator will screw up the differance pressure between upper and lower chambers in the fuel distributor, hence the lean mixture (duty cycle ~30 %).

lear60man · #8 06-18-2014, 02:42 AM

Quote:

Originally Posted by 190dee

Did you ever sort this problem out? I notice a leak at the small rubber hose on the back of the fuel pressure regulator. The problems I have is that the engine stalls very intermittent.

If I understand it right there should not be any leaks at the rubber hose since it's just a precaution to lead fuel from the regulator back to the intake if the diaphragm breaks. And a faulty regulator will screw up the differance pressure between upper and lower chambers in the fuel distributor, hence the lean mixture (duty cycle ~30 %).

I understand it to work like a diaphragm with one side air (vacuum) and the other side fuel. if fuel is leaking to the other side, the internal diaphragm is ruptured.

liquiddog · #9 06-18-2014, 07:34 AM

I'm trying to imagine how there could be any significant amount of vacuum at the connection point. Mine goes essentially to the air box (on the breather tube).