Need a diagnosis - PeachParts Mercedes-Benz Forum

Max J. Sandler · #1 09-16-2002, 09:57 PM

I've written in about problems with the fuel injection system on my 87 560 SL with mixed results. Here's a symptom that give someone a clue as to what's wrong. The car seems to run okay, but starts hard hot or cold, and gets very poor gas mileage. If I play with the mixture adjustment, it will vary the idle speed considerably. When I lean it out to where it idles correctly, it won't start at all. If I can live with a high idle, it will start, but still cranks too much and uses too much gas. Some of the suggestions I've received to date include the fuel accumulator, pressure regulator, and taking it to the dealer (ugh!). Its my understanding that adjusting the mixture should have no impact on the idle speed, since the system is self-compensating.

If anyone has experienced a similar problem, or has any ideas (other than going to my local dealer, the thief), they would be greatly appreciated. $ 100 to the person that nails it!

joe p · #2 09-17-2002, 07:40 AM

you need to check the duty cycle and perform a fuel pressure test. hard CIS starts are leaks internally most of the time. there is no reason to go to the dealer, find a indy with experience in diagnosing CIS-E cars.

how does the car idle once it starts? is it lumpy or smooth? lumpy idles are related to system side leaks, smooth generally are realted to control side leaks. i saw one that the c/d box-EZL was bad and just had a 103 car with a weak ign coil mimicing a loss of rest fuel pressure. food for thought.

Joe

stevebfl · #3 09-17-2002, 08:19 AM

Your technique suggests a lack of awareness of how this system works.

The act of adjusting the mixture till something changes, is to overwhelm the system both ways with proper system activity somewhere in the middle. This system can not work right unless it works period. Doing the adjusting you have done guarantees that the system can't work.

Read the DIY article about Evaluating Engine Controls in the DIY section of this site. The testing is very simple and done with common tools.

When working properly the system can be properly adjusted and monitored with a decent voltmeter. If its broke, it gives diagnosable data.

Max J. Sandler · #4 09-17-2002, 10:34 AM

Your point is well taken, Steve. I guess, in my frustration with the situation, I'm looking for a shortcut. What makes it all the more frustrating is that my 560 SEC with 50% more miles and virtually the same drivetrain, has run flawlessly since the day I bought it.

It appears that also I'm dealing with the previous owner's lack of competent maintenance. Thanks for your reply.

sublettd · #5 09-17-2002, 01:11 PM

Steve,

I often see references to the DIY section of this site, yet I have never been able to find it. I'm not blind (I don't think), but I could follow a link if you or someone else would be so kind as to post it.

Thanks!

stevebfl · #6 09-17-2002, 01:19 PM

I am pasting it here but it is at the top of the page you are looking at. Just go to DIY out of the list above: Home, Shop Forum, fastlane, PartsShop, D.I.Y., Cars, What's new Links.

http://www.peachparts.com/do_it_yourself.htm

sublettd · #7 09-17-2002, 05:46 PM

Steve,

Pardon me while I SMACK MYSELF RIGHT BETWEEN THE EYES IF YOU WILL!!!

Thanks,