As title states, can the fuel pressure regulator be checked or does it have to be replaced?

And if it can be checked, how?

Its for a 1988 300TE.

Thanks guys,

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

its checked by checking the fuel pressure. need to get the info for that. you do need an mb style gauge setup.

george

So I can't check that myself then if I don't have the special gauge? Are they expensive to purchase?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

correct. you need to have a gauge setup and the knowhow. what/why is the problem that makes you ask?

george

I have a misfire in my engine and am slowly routing out possible problems.

I have replaced spark plugs, ovp, wires, injectors + seals, rotor + cap...Vacuum Test came out good. Compression is excellent....

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

yer on/off ratio needs to be checked. you might have a lean condition. there is info here on how to check that but again you need some tools. also really helps to have a c.o. machine to read yer exhaust. and a scope. might really be time to have a shop look at it. without a smoke machine you really don't know if you have a vac leak or not.

george

I followed the directions in the DIY article on how to use the O2 sensor to check for Vacuum leaks. The test came without any leaks, as I suspected beforehand. If by the on/off ratio, you mean the Mixture, we have adjusted it numerous times (including the mercedes repair shop I took it to for diagnosis, which of course he couldn't find the answer to my misfire).

This isn't something simple otherwise we would have had it fixed by now and the previous two owners would have figured it out.

We have also changed valve stem seals, voltage regulator, fuel filter, O2 sensor and vacuum hoses.

I am getting pretty certain that the Fuel Distributor is the problem here as the Mercedes repair guy said there was "rust in the fuel distributor"...but before I replace the Fuel Dist, I want to make sure the certain prerequisites are checked before I go and purchase that relatively expensive part.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

oke dokey. this has been a long issue with parts thrown at it. what i see now is to nail down if its the fuel dist. whenever i suspected a fd/inj issue i would do a flow test. i would get the appropriate # of small bottles. i would take out the inj with lines attached and insert the inj into the bottles. then jump the fp relay. press down on the flow plate and let it "inject" for at least 30 seconds. then i would see how off the amounts are. a cc or two is enough to make a differance. if one showed a big amount i would install a new inj. if this fixed it, great. if not then it pointed to the fd. the fd has a small plastic screen at the outlet port were the inj line goes in. see if its plugged. if so take it out and retest. you get the idea. if you got rust you need to check yer tank and fuel filter. normally a miss is first diagnosed as to if its fuel or spark related. this is done with a c.o. meter and then according to the results one goes in that direction. this was not done. a miss with low fuel will give you a high h.c. but not extreme. a spark miss will give you a very high h.c.. so go from there. george

Well here's my smog test ran 3 weeks ago


The car only just passed, but it was running very rich at the time.
It only just passed when idling, but was well under the limits when it was at high rpms.

That is a great idea on how to test the fd. How would I jump start the fuel pump relay?

We replaced alot of those parts as they were cheap to do (well the valve stem seals needed to be done as I was losing oil). I was just replacing the cheap parts before I thought about spending more on the other stuff.

I bought the car for $3000 and have probably not spent more than $600 in parts (most of that was for new brakes!) in the 18months I have had it. The car is in amazing condition...it's just this darn idling misfire!!!! Very frustrating!

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Since a misfire is usually on one cylinder only (at a time), I would think the pressure regulator very unlikely a cause. If you describe in more detail how and when you notice the misfire, someone here might be able to give you a more directed suggestion. Note that a diaphragm leak will send gas out the 'vacuum' line of the regulator - an easy check.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Ok I'll try my best:

It happens regardless of heat and is completely inconsistent. It is ALWAYS felt, but some days its relatively smooth and others its an absolute earthquake. There is no consistency for the misfires. When the car starts up there are no misfires for about 10 seconds then they slowly start to kick in and continue for the rest of the journey (once the car is warm, every time I start up misfires happen right away, only when cold it doesnt misfire for ~10seconds)

Acceleration as I said above is 110% smooth. No hesistation and the car will run without any hiccups at the red line. After we replaced the valve stem seals I had the car out on the freeway for several miles on the redline to flush anything out and it goes like an absolute dream. Its ONLY idling at stop lights or just simply stopped anywhere. As long as the engine is on and the car isn't moving, it is misfiring. This indicates no exhaust back/cat problems otherwise it would have problems at higher rpm's too, not just at idle.

I have pulled each spark plug individually while the car is running and it makes no difference to the misfires at all.

Its not engine mounts as you can hear+see it misfiring.

The compression rates are great:
1/ 180
2/ 180
3/ 185
4/ 185
5/ 195
6/ 190

Here you can see the quality of my engine:

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

I am just going to relate the times I have had this problem with my 500SEL.
1. Found someone (Maybe me) used a coil wire that had resistance in it.
Probably just something lying around.
2. Found a oil fouled plug. Not completely, just some.
3. Used Bosch plat plugs with resistance. Did this on a bet that it would
cause a missfire at idle. I won the bet.

I have replaced the coil wire with a new correct one. Replaced the valve guide seals.
Installed NGK BP5ES non-resistor plugs. Now I have to keep checking the tach when at a light to make sure the engine is still running.

The above things didn't come all at once but one at a time over the last 5 years. I know vacumn leaks can also cause this problem but seems you have ruled out that. Just make sure you are using NON-resistor copper core plugs, Solid core wires with the MB resistor ends called for, and you should be able to get rid of this problem. Good luck.

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84 500 SEL (307,xxx miles)

I am using OEM Bosch H9DCO's which are the proper non-resistor ones. This problem is somewhat more complex as this misfire has happened to my guess, for probably anywhere from 20,000-40,000 miles(I have personally done 15k of that myself) as the past 2 owners spent several thousand dollars at the shops getting the injectors done, suspension, and other things and thats why I got the car so cheap because they were sick of having the thing misfire and stall randomly (we fixed the stalling with a new OVP and valve stem seals).

My ignition wires are the Bosch ones found on MBShop
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=28018N5L828H0P5I3M&year=1988&make=MB&model=300-TE-001&category=F&part=Ignition+Wire+Set

So sick of the car shaking every damn time I step into the car. It's so frustrating that I haven't been able to fix it. The Mercedes Repair shop that I handed it to diagnose the problem basically was a waste of my money as the guy said "in my professional opinion you should leave the car alone as it could be too many things and would be expensive. The car runs great so I would leave it alone.". Well thats great huh? I wanted to know what it could be, not that I shouldn't fix it.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Unless I missed it, I don't see that you have replaced any of the idle air circuit or intake rubber. If this tubing is not soft and pliable, it could have cracks, and at least will not seal properly at joins. I would replace all this rubber - it is pretty cheap if purchased here. Don't forget the lower part of the air intake plenum too. Also clean the airflow meter vane to insure smooth operation when slightly open. A problem in either area would be much more noticeable cruising and under very gentle acceleration than full power acceleration. Typically idle might be a bit high and erratic, too.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Do you mean the breather hoses? If so, yes we have replaced all of them as they were rock solid before. Forgot about that.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k