Can Fuel Pump Relay be Checked?

If you have an intermittent stralling, no start or hard start, and the relay is old, change it out of hand. You can pry off the cover and carefully examine the solder joints to see if any are cracked or have a frosted appearance, this may confirm the likelyhood the relay was causing your problem, but change it anyway. Newer relays are both, well NEW, and also they are updated internally.

Bill Ditmire Ditmire Motorworks,Inc.

425 White Horse Pike Absecon,NJ 08201 609-641-3392

I drive an 87 300e manual, no cat, no lambda.

In my search throguh this forum, I've found there was a change in fuel pump relay in 1987, part number 002 545 27 05 up to engine number A396764 and 003 545 24 05 for engines after that.

I've just checked my new relay and discovered the part number is 003

545 24 05 but the engine number is A3510xx, which means I should be using the 002 relay.

Now, the engine runs fine apart from the fact that it starts cutting out at 4,000rpm when driving, but not when in neutral or with the clutch in.

The fuel pump relay was replaced as part of a whole series of new bits solving a rough idle/hot start combo, which is now cured. I've also changed the fuel filter, OVP, all injectors and all usual suspects, incluing rotor and cap.

Does anyone know what was changed with the new relay? In particular if there was an introduction or change to the rev limiter element.

I need to know if there's any connection to my problems and whether I can fix or disable the rev limiter before I have to track down the old part and pay for that just to test it out.

Anyone running an old 300e with the new part without problems?

If a rev limiter were causing the engine to cut out it would cut out in neutral as well as under load but it only cuts out under load. That would be a result of fuel starvation, IMHO.

The most fuel is used during acceleration and hill climbing, also at high speeds. You don't mention any problem with hill climbing or acceleration only consistent high speed under load; that suggests gradual fuel starvation - weak fuel pump or dirty fuel pick up or restriction in the fuel line or kinked fuel hose etc.

Thanks for the tips. However, I'm unsure that fuel starvation is the problem. The engine pulls strong up to 4,000 rpm and only at that point does it start to buck, until the revs drop below 4000 when normal service is resumed. No trouble accelerating up hills, even with a full complement of four adults and corresponding golf clubs. That's what makes me think something is cutting supply to the engine when revs reach 4000.

I have read that automatic versions have a limiter that prevents the engine from being over revved in park and neutral, and that the restriction is removed once the car is underway. However, my car doesn't appear to have a Hall effect sensor which is part of this process.

As the FPR is the new type - my car is supposed to use the old 002 relay - my suspicion is that the relay is expecting to be told that the car is moving but isn't receiving a signal. Hoever am finding it hard to get any information to back up this supposition.

This weekend I plan to remove the relay and bridge the connection to see if it happens again. That should give me some more pointers.

I saw this problem on an 87 300E automatic. Turns out it had a FPR for a 4 cylender car. Look at the top of the relay and see if it says "4 zly" or "6 zly" or something like that. Or the FPR may just be bad.

PMcKechnie

84 500 SEL

Thanks for the heads up Paul, I'm pretty sure now it's because I've got the wrong relay in there so I'm going to change it sometime in the future. Not a major issue as I don't need the extra revs driving round here so will put it on the list of things to do. This month the $100 restoration money goes on new front rotors and pads, next month its door and boot seals

cheers