Straight6

Hi All,

I have an '85 500 SEL (Gen 1) which I've been working on for a while. Recently, after a fair bit of work to solve vacuum leak/high idle I was on the way to the MOT but quickly put the car back on the drive as I forgot something and haven't been able to start it since.

The car struggled to start and if it did run, would idle roughly and then die. Suspecting a fuel issue, I jumped both the fuel pump and the relay to no avail. Both the fuel pump and filter are very new.

Today, I noticed a small leak around the fuel pump so replaced some worn fuel line and a washer - leak fixed. The car will now start after a few tries and after a shaky start start will idle ok. However, as it now runs for a bit longer, I've been able to observe a new symptom - the engine dies as soon as I touch the accelerator.

Does anyone have idea what this might suggest and the next troubleshooting steps?

JohnLane

She has K-Jet for injection? You describe a false air leak. This the most common issue with K-Jet equipped cars.

Start with testing for a false air leak with smoke. Don’t have access to a smoke machine? Look long and hard at all the rubber guys that handle vacuum, feed the idle air bypass valve ect. Usually one or more of them are cracked + leaky injector seals.

Start there.

Straight6

Yes it's K-Jet.

It's not a vacuum leak - it did used to have one but that was all repaired recently with a smoke test and replacing all the cracked hoses. The symptoms for that are different anyway, you can usually keep the car running if you keep on the gas pedal. Experienced the same thing with a 190E previously.

Straight6

Does anyone know much about the ignition module (EZL)? I just followed a test from the workshop manual where you are supposed to be able to see battery voltage reading from one of the pins to ground - mine shows zero.

The manual says that means it's faulty and needs replaced but before chucking money at it, i wonder if there's any other electrical issue that could also cause that result.

adler

As you do the diagnostics It would be a good idea to clean the connector pins for the idle switch at accelerator linkage , air flow pins and idle control valve pins. Old fuse box fuses do cause odd issues if all the fuses have not been replaced .

Straight6

I've made some progress. Before sorting out the idle issue previously, I had to drain the tank as the car had been sitting for a long time. By doing so, I may have inadvertently clogged the fuel filter. I had dismissed this initially as the filter was so new and didn't think it could clog so easily.

Anyway... changed the filter today and the car now fires up and doesn't die when I touch the gas. However, it revs horribly; hard to explain but it judders a couple of times before actually doing its job. It's still a big improvement so now I want to look at the fuel tank screen but that requires the tank to be drained....

Any ideas how to tackle this without clogging the filter again?

ygmn

sure none of this crappy fuel got to injectors etc?

adler

There is a very fine mesh filter at the distributer inlet connection. Occasionally we forget that this critical filter requires a checking up.as well when doing a major service .

Straight6

Yeh checked that already. Think i will just have to drain again but remove the tank and clean it out before replacing the strainer this time.