560 sel hesitation - PeachParts Mercedes-Benz Forum

demeterial · #1 03-06-2004, 06:26 PM

hey ladies and gents Ihave a 91 560 sel that was hesitiating from stop lights and idling rough for about 5 sec and then would smooth out perfectly well.. I found a loose wire on a temp sen sensor of some sort going to the radiator.. reattached it the car is missing so much less now.. Ill get it tuned up with new rotor cap plugs and wires.. and that should solve the slight misses and hessitation ..
Thanks

demeterial · #2 06-20-2004, 06:52 PM

hello ladies and gent's I have been trouble shooting for a couple weeks whenver I can find time.. heres what I did.. I removed and inspected the O2 sensor... i seemed fine no carbon build up at all in fact it looked practically new.. removed the fuel pump relay and the car would not stay started.. so I think thats working..removed the OVP relay and the car would not start at all.. removed the EHA valve connector and it ran more rough than usual.. I removed the connector to the IDle control valve and the engine speed does not increase..I switched the wires around.. again nothing changed..well it would not stay started more than 3 secs I should say.. I removed the Idle control valve and visual inspected.. it was filty I barely discern the internal components but it does vibrate when current is applied.. so I not sure if its stuck or needs to be replaced or cleaned.. now the gentlman who owned the car before me just totled around town it so Im sure it was never blown out the way it needed to be...also after the car wrmed up the OVP relay was very hot to the touch at one point I could barely handle it and spark is minimal at this time as well I think I needs replaced because it was hard to start after operating temp had been reached... the idle was a bit rougher as well.. there was no fuel smell around the distributor or the EHA so I think they are ok .. as I could push the plate down in the fuel distributor and revs picked up but only to a certain point before the engine stalled.. wich I feel is due to flooding with fuel.. as when the car is in its rough idle state the economy needle on the dash is all but in the red.. again this is in idle.. so anybody got a spare ICV and OVP relay for a 91' 560 sel for sale
Happy Fathers Day

demeterial · #3 07-01-2004, 09:03 PM

hi here is the latest edition of my saga.. I have replaced plugs wires cap/ rotor/cleaned ICV and replaced coil.. the car idles almost perfectly now but when I press the gas it al but stalls.. now when the engine gets to operating temp and the O2 sensor kicks in the eco needle goes into the red as the eha is trying to keep the car on.. I think my fuel dist is bad/clogged/fouled some how.. will crawl under the car tomorrow while its running and make sure there is no fuel lines crimped or anything.. but I think I have a fuel issue.. had the pumps checked and they are fine as well as the filter.. prob just got some bad gas will try the fuel additive issue as the litmus test and barring that I am at a loss..

jeffmg1 · #4 07-02-2004, 08:15 AM

Hello
I think I would like to make a suggestion on how to fix things.
I would have some test equipment and check the operation of relevant parts to a system that is not working properly.
Most likely there is one culprit to your problem. If you replace 10 things to fix it, 9 of them were good!

For your hesitation I woluld hook up to the EHA and monitor the current. I would check voltage on fuel meter plate position pot.
Check throttle switch. Check resitance of coolant temp sensor. ETC.

Other things to check. The fuel meter plate should be in the proper position and move smoothly. When you pull the plug off the ICV the RPM should go up to about 1500. When engine is at operating temp removing eha plug should not afffect idle.

This is a very good forum. If you do tests and post results. I think you will get help.

demeterial · #5 10-21-2004, 07:09 PM

hey guys heres the latest update.. I have finallyreplaced the fuel dist.. the car ran like a scaleded cat for about 5 min and then went into limp mode.. the tech says he barely made it back to the shop.. now it wont start at all.. hreplaced the eha and the plate sensor as well.. I am considering selling and getting out the benz game.. I have another tech in Tulsa here in OK I may have look at it.. but I just dont have time to devote to it.. sorry guys i feel like Im letting you down.. but there was fuel pump or filter problem and no dist prob and no O2 sensor problem.. hope this helps everyone
D

psfred · #6 10-21-2004, 07:37 PM

That's what happens when you throw parts at it without determining the cause of a problem.

You have a bad OVP -- if it gets hot, the solder joints are bad and causing excess resistance.

Replace the O2 sensor unless you can verify that it is working, they don't last forever and appearance means nothing, it has to be electrically verified.

Your hesitation was most likely bad idle control valve hoses (rock hard, eh?) causing a vac leak. Idle valve can be cleaned with carb cleaner spray, it shouldn't have residue in it.

A bad fuel pump relay will cause intermittant stalls, rough idle, and mixture control problems from inadequate fuel delivery. So can bad fuel pumps.

You now need to properly set idle mixture, it's probably way off -- when the computer attempts to control the mixture it goes overlean and causes low vac, rough running, etc. This is probably more vac leaks, there are a number of sources.

These can be expensive to restore..... Much more expensive it you start replacing things to see if they are bad!

Peter

demeterial · #7 10-21-2004, 10:19 PM

Thats not what I was trying to do.. you must understand that the local Mercedes tech is 80mi away.. so I tend to depend on the limited knowledge of the local techs..so with my limited time and knowledge base I have to make the best decision I can... the only things I did replace were the fuel distributor because this town is notorious for bad gas.. replaced the ovp relay because it was hot to the touch.. and regular maint parts i.e plugs/wires cap/rotor.. there was/is good pressure from the pumps and to the distributor the hoses are ok at the idle control valve.. cleaned it car runs much smoother..fuel pump relay was tested and found to be in working order.. there was an attempt to correct the mixture as best the tech could because all of the things you mentioned were tested.. the expense is not such an issue as the cars are underestimated in this part of the countras far as their value so parts are kinda cheap.. next time I will spell out the testing done a bit more.. again I have not been throwing parts at the car.. I am very far from assumptios and reactionary.. I have literally hundreds of hours spent dxing the prob and 3 sepearate visit to local shops testing every obvious link in the "chain" leading to a better running car..if I were throwing parts at the car it would have taken much less than the 5 mos its taken to achieve the limited amount of "success" I have

psfred · #8 10-21-2004, 11:41 PM

Idle mixture must be set with a duty cycle meter or the diagnostics tool, duty cycle works fine (pin #3 of the diagnostics connector, the round one with a screw on cap). Lots of posts on this, and it may cure most of the problem. Just twiddling with the screw usually makes the problem worse. You can get close with a CO meter, but it's much more difficult. Set duty cycle to near 50% at idle, hot, value must float.

Timing is mapped and computed, so if it's off, it's due to a bad temp sensor (I don't know the values, but they can be checked with an ohmmeter) or bad crank position sensor. Worst case is a bad engine ECU or ignition box, both rather expensive and I wouldn't replace one without knowing it's bad.

A leaking injector will give you fits with idle mixture, too -- rough idle, stagger on takeoff (because the dripping one is causing the computer to set the rest too lean), but will run fine at higher rpm.

Peter