1982 245 K Jet stalling and intermittent start issues

Brand new to the forum. I have searched far and wide trying to diagnose my 1982 240 wagon K-Jet and am striking out. The other day the car died on my wife while going up a pass and then wouldn't restart. I got to it after sitting and it started up hard and I drove it home another 50 miles. 1 mile from home it started sputtering and lost power then died again. By this time it was very hot out and i had noticed the temp gauge started going up as well. Couldn't get it restarted so i went and tried it much later after it had cooled off outside. It started up and limped home, chugging a bit.

First thing i thought was to replace the fuel pump relay. The old relay had signs of overheating at the main power supply terminal. I thought that had to be it. So i replaced it, and tested the car up to operating temps and WOT several times. It seemed fine. I felt the relay and it did seem to get a little warm but nothing too concerning. Drove it for an hour and now am noticing that after the car has been sitting in the sun and heat it will turn and turn but won't start. It starts up in the morning but for a long time it has taken two tries. First try it catches but dies immediately. Second try starts it up fine. Also, after the hour drive the other day it started idling very high and holding (guessing around 1500-2000 rpms) even after i gassed it a couple times thinking the throttle cable had just caught.

I ran a jumper on the fuses to both fuel pumps several times and could hear that they are both working. However, I have noticed a sporadic cavitation sound from the main pump. Also replaced fuses for both pumps and flame trap. Recently replaced plugs and wires. Did drain and fill of coolant. I am sort of stumped. My next thought is to do the fuel filter and clean IAC? Any thoughts on why a cold engine but warm car is causing a no start condition?

Eliminate any possible relay problem completely. Rig up a toggle switch and some leads to replace the fuel pump relay. Do you have a manual with wiring diagrams?

Thanks for the response! I have a green book manual but from what i can tell, it doesn't cover the kjet relay wiring very well. So just try to bypass the relay to run the pumps? The wiring harness is a little melted around the main 12V power terminal, could be part of the problem?

Your description of the problem would have me checking the intank pump. Then I'd move on to doing a fuel system control pressure check. The cavitation sound could be from a non working intank pump setup. The description of how the car starts in the morning is like having high control pressure.

Agreed cavitation seems like low fuel supply from in tank. However, i could hear the in tank pump running when i jumped it from the fuse box. Can you help me understand high control pressure?

I continue to struggle with K-jet knowledge after many years of ownership.

You really must have fuel pressure test equipment to diagnosis the K-jet system.

The lift pump in the tank fails and causes random problems with less than half tank of gas.

The lift pump fails by internal failure and by failure of a 2" hose between the pump and the metal tube to the rest of the car.

Remove the hose at the input to the pressure pump and spray it into a bucket to ensure that it works. Low pressure, about 7-8 psi.

Now you have to have a fuel pressure test kit to test the rest of the system.

Fuel pressure at cold start at the input to the Control Pressure Regulator should be 24+ psi.

That should rise to 48 psi + hot. That is the HIGH CONTROL PRESSURE you asked about.

System pressure should be about 70 psi.

Further information here: http://www.turbobricks.com/forums/showthread.php?t=289775

For wiring diagram PM me your email address. Posting images here is a hassle.

I used a second relay to turn on the fuel pump relay, because K Jet fuel pump relays are really crappy. Unplugging it can break it, got a pile of broken ones to prove that. If you need pro help beyond what you can get on the internet, look for a local Mercedes specialist. Mercedes use K Jet way longer than Volvo, and the experts are easier to find.

UPDATE: Thanks to everyone for the help. After pulling injectors, cleaning them, replacing o rings and holders, replacing fuel filter, checking vac leaks, replacing fuel relay, testing fuel pumps, jumping coil to battery terminal (i've heard this is an issue that creates fuel starvation symptoms: it was running but really poorly, kept trying to die. I finally pulled the in tank pump and lo and behold the hose in the sending unit was gone entirely (probably eaten away by ethanol?). I believe I found my problem!

I have parts on the way, and if that doesn't solve my issues I will be truly stumped.

did it end up fixing the issue. I'm having this super weird intermittent stalling issue. earlier today I stalled while going down hill with less than half a tank of gas. when I came to a stop on flat ground I tried to restart the car but it wouldn't even sputter. I got towed home and started taking things apart. took off one side of my fuel filter to see if any fuel would come out when I cranked the engine over. fuel came out. so I hooked it back up and tried to start the car. started great. took it for a drive around the block to see if it would stall out again while I was driving. it happened again on flat ground, on decel. I tried to pop start it before I came to a complete stop and it started and ran fine. I'm so confused and honestly baffled with this issue.

1981 240 m46

Random stalling can have several causes. High control pressure, vacuum leaks, bad spark plug wires, worn out spark plugs. It's time to do some maintenance and eliminate multiple possible issues.

dl242gt said:

Random stalling can have several causes. High control pressure, vacuum leaks, bad spark plug wires, worn out spark plugs. It's time to do some maintenance and eliminate multiple possible issues.

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within the last 200 miles I did spark plugs, wires and the ignition coil so I'm pretty sure its not the ignition system it seems like the fuel system to me since whenever I'm having the no start, I pull an injector and crank it and have no fuel come out. I'm just reaaaally hoping its not the electrical system. I already had to clean re pin and put a new connector on my fuel pump relay (as well as a new relay) and I just really don't wont to start going through the whole car looking for gremlins

I chased issues with mine for years, rebuilt fuel distributor, new injectors, fuel pumps, accumulator, cpr, etc. Turns out the issue was the original distributor. The internal parts deteriorate and will cause all sorts of issues. Putting a 123 ignition on the car transformed it. Best thing I've ever done.

If you don't have fuel during the stall/no start. Then you want to check the signals at the fuel pump relay. The white/red wire comes from the coil. It makes the relay turn on when it detects an engine rpm signal. So, check that wire connection on the coil and in your redone wiring.

If that stuff is all good. Then I'd move toward checking fuel pressure from the main pump when the problem happens.

It's probably the fuel pump relay. K-jet fp relays are such a piece and so overworked for what they are.

dl242gt said:

If you don't have fuel during the stall/no start. Then you want to check the signals at the fuel pump relay. The white/red wire comes from the coil. It makes the relay turn on when it detects an engine rpm signal. So, check that wire connection on the coil and in your redone wiring.

If that stuff is all good. Then I'd move toward checking fuel pressure from the main pump when the problem happens.

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I checked the red and white wire and it looks good where I repined and crimped it and in the engine bay. but then I looked at my hall effect plug and I think I found my problem. I recently replace my alternator and when I was looking at the wires going from the hall effect sensor they run right on top of the alternator. I was putting weight on the alternator so I could tighten the bolt tight enough and I think I might have pulled the plug out of the distributor a bit. going to check the wiring to confirm my theory.

Sounds good. I've had that inline connector for the distributor harness fall apart from heat and age taking the wiring connection with it.