Warm engine dies and wont start up

[Travis71280]

Is the stock fuel pressure regulator the thing that screws into the return side of the injector pump or the circular diaphram looking thing just down from it? The former is still on it but the previous froze up and had to be drilled out.

[Naj ✝︎]

Awesome, that saves me from crawling under the car again, also feel better about changing the points. Where is the bleed screw exactly?

On the front of the filter head. 10mm hex head/screw driver slot.

naj

[thelews]

In general, I find this injection system to be well designed and it will work well as a complete package. If you change anything on the system, it won't always work out. Everything has to be balanced to work in harmony if you want to get everything out of it that it can give you.

You mean a bunch of at-home amateurs can't outsmart MB engineers, even from the 60's?

[Naj ✝︎]

Naj, how does that test work? It's something I haven't thought of or used.  

Hi, Dan,

I had similar issues as Travis when I bought my first Pagoda in 2001.

I never suspected fuel problems as the FIP had been rebuilt, electric pump replaced and the tank new looking.
Besides, all this technology was alien to me except for being similar in diesels.

One day it stalled in traffic and I just wanted to check if there was fuel flowing, thinking the filter may have clogged up and undid the bleed screw.
After letting the warm fuel run out, I had 15 more minutes of drive time.
I think when there is no fuel circulation, the fuel in the pump chamber is just churned by the rotor and heats up and eventually evoparates, causing fuel pressure loss. Thats my theory anyway, and it worked for me.

Eventually, a big hole was cut at the bottom of the tank and the clogged return line cut out and replaced.

naj

[Benz Dr.]

Well John.......  I learn about stuff every day, so I suppose I'm NOT a smart as a fifth grader or even a 1960"s MB egg head. 

Naj, I see what you mean now.  If the fuel doesn't circulate it will get hot and vapour lock. It's absolutely essential that you have fuel pressure, fuel volume, and fuel circulation. If any one of those three items are absent, you WILL have running problems. Some will prevent the engine from running and some will make it run poorly, or not at all.

[Travis71280]

Hey everybody, found something, i tested the fuel pressure where the hard fuel line comes into the cold start solenoid is on the manifold side and I'm only getting 7psi without the engine running. Do you know where I can get a new fuel pressure regulator, how much does it cost and possibly the part number? Could this be the cause? The only thing that confuses me is that the engine will run smooth even on hard acceleration and like I said start stalling out once it gets warm.

[Benz Dr.]

It could be all three things. Low fuel pressure from the pump, not enough fuel pressure because of the regulator and a plugged return line.
If you squeeze the hose going back to the tank the pressure should raise if the pump is working OK.
 I would take a reading right off off the line coming from the pump. If your pressure is OK there then it's more likely a pressure regulator problem.

[Travis71280]

Well, its the fuel pump (7.5psi directly at the pump). Trying fixing it and going to check it again. (By the way, that little pressure regulator costs $170 )

[Travis71280]

Well, its definitely the fuel pump, 7.5psi, again.  Recken that was the problem the whole time?

[Benz Dr.]

Make sure you check the filter screen right at the fuel pump. Not likely messed up but you never know. I took my pump apart and sanded the bottom cover which brought the pressure back up. It was worn quite a bit and it made a difference.
 Use a piece of glass and stick a round sandpaper disc to it. Swirl the bottom cover over the sand paper until all of the scoring marks from the impeller are gone. This won't change the basic distance betwen the impeller and bottom cover because it's all part of the pump housing. If this doesn't improve your pressure the pump is probably worn out or dragging - maybe time for a new one.

Your fuel pressure values are right at the minimum I'd say. I should have a check valve from a dead pump laying around here somewhere.

[ja17]

Hello,

The drain plug/screen assembly in the fuel tank should be removed and checked also. Also check the filter screen in the fuel pump as Dan has indicated, and the main fuel filter.   If you continue to get dirt or rust in any of these you will have to clean, or replace the fuel tank.  Make sure that the return fuel  line fitting ( on the injection pump) is correct.I guess this is what you call a regulator?  It creates the correct fuel pressure (back pressure)   in the injection pump. Yes a good point by Dan, to squueze of the return line for a test.

[Benz Dr.]

Joe's information is solid as usual. Those things to check are a mater of course.

[Travis71280]

I'm going to try to sand the impeller housing like you said and see if that helps. The motor I think is still good. I had previously tore everything down and the insides looked clean and the brushes still look good. All the O-rings have been replaced, but I sounds the impeller is rubbing a lot. While I got it out ill check the filter. The tank should be good since I just relined it with POR15 (turned out real good, except the fact that it clogged up the vent lines, thats a whole other issue I got to address which also causes the car to stall). When I did the pressure test, I hooked the fuel pump (not the injection pump) output directly to my pressure guage. You were right, thats what I was referring to as the pressure regulator (the MB dealer did find one, $130 dollars PLUS tax). Is there an aftermarket setup (pump and regulator) I can do that has been used that delivers the right pressure and flow until later on where I can afford to do it right? Didn't someone successfully use a pump and regulator from a Saab? I've been looking for a pump that delivers at least 180lph and delivers at least 15psi but there really pricy (above $100 for either the pump or regulator seperate) or questionable. I'm still going to try to get the pump to run though. Thanks again for all the help.

[Benz Dr.]

What you're looking for is low pressure and high volume. The volume keeps the IP cool and prevents vapor lock ( usually )
The round thing below the regulator is a fuel dampener. It's supposed to smooth out the fuel pulsations coming out of the IP.

[julianmaba]

Travis, have you had a chance to check that you do have healthy spark at your spark plug leads (as per earlier advise) - checked when the engine will not start (after that initial 15 minutes of running well). If you have no (or poor) spark when it dies, it will not matter what you do to the fuel injection system, it will not run.  Do you have spark while you are cranking and trying to start?

[Brian Davidson]

i have a somewhat similar problem. my 280sl runs fine but after about five minutes following a cold start the engine speed gradually slows until it stops. when the engine is fully warm it idles normally. i can make it idle during the problem phase by giving it some throttle. the electrics are in working order and the warm running device has a new filter and a progressive decrease of the hissing noise. also if i detach the linkage and increase or decrease the fuel to air ratio it does not indicate either a too rich or a too lean mixture.co levels at idling and at 3000 revs are correct when the engine is fully warmed up. excuse no capitals. i sort of touch type. i would be grateful for any suggestions.   

[ja17]

Hello Brian, 

A very unusual problem!  Make sure the intake venturi is adjusted correctly closed and the rest of the linkages are set correctly.  Also the be certain the ignition timing is ok.

After these items are correct, I would start out by adding a oval shim under the WRd.  This will increase air and fuel supply during warm up. You will still need to make sure that the WRD air supply closes after warm up. If this does not hel, simply remove the shim to get back to where you are now.

[Brian Davidson]

Hello Joe many thanks for your helpful reply. it is an honour to recieve advice from such a distinguished member. i am at present unable to unscrew the two screws on the wrd but am applying wd40 in the hope that it may ease them. in the meantime i plan to carry out some further experiments and again consult the BBB. may i get back to you when i have more information. best wishes Brian.

[ja17]

Hello Brian,

Take a blunt drift (metal rod) and smack each of them with a hammer, then they sould unscrew.

[graphic66]

I like to get a very tight fitting screwdriver and turn it while hitting the top of the screwdriver with a hammer. If you do a lot of your own work a hand impact driver can sometimes be really handy, here is a high quality one  http://www.toolup.com/klein/70220.html?AdCamp=CA&utm_source=CAnextag&utm_medium=CA&utm_term=klein+70220  There are also many cheapo ones out there. This tool is a must have for the phillips head screws on the engines of motorcycles, I also needed it to take apart my rear brake compensator on My SL. But, you probably will get it out with a little simple impact in this case. Remember, when reinstalling to put a tiny bit of never sieze on the screws. It will save you the trouble if you need to take it apart again. You should use the never sieze anywhere aluminum is used as a thread, like the spark plugs.

[Benz Dr.]

Use nickel anti seize only. The copper stuff isn't for aluminium parts.

[ja17]

Hello Travis,

Don't forget that if a good fuel pump is trying to suck in fuel through clogged fuel screens or a clogged fuel tank, the fuel pressure will be low.

[Brian Davidson]

Many thanks to you all. Managed to loosen the famous screws and remove the wrd.The pin moves freely. As I do not have any extra washers I loosened the screws which made the engine run slower both during the troublesome phase and when fully warm. I should have mentioned that the engine needs a very small degree of throttle to start from cold otherwise it dies immediately. Then instead of idling at 1000 to 1200 RPM it idles at 600 to 650 RPM and then drops further when the temperature needle nudges the one 180 degree square. After a a short drive of a few miles it idles at 750 to 800RPM. Oh what can the matter be?It is causing endless sleepless nights.

[Travis71280]

Well, finally broke down and got an aftermarket fuel pump. Its a TRE Performance 255lph inline universal fuel pump thats based off a Walbro fuel pump design. I'll keep you all posted when I finally install it. I'm hoping this will fix it, but I've said that a before . Thanks again for all the input.