Fuel pump relay failure symptoms: engine stops, hard cranking and high idle RPM KE Jetronic Benz

Fuel pump relays on older 80s and 90s Benzes do much more than just turn the fuel pumps on and off. They can affect engine idle, O2 sensor, climate control, and of course the engine's fuel supply. This video explains what some of the failure symptoms can be when this parts malfunctions.

[@Cpcsof1]

I coincidentally replaced my FPR today due to the engine shutting off 3 times last night on a 120 mile trip. Today, I drove 250 miles with no issues.

[@straybenzes]

Hopefully you have found your intermittent shut off issue. It is quite annoying right?

[@Cpcsof1]

@@straybenzes Extremely annoying if it shuts off in traffic.

[@straybenzes]

@@Cpcsof1 ...and dangerous. It did that to me on a three lane highway and I was in the left lane.

[@nadk8886]

​@@Cpcsof1 hi, this happened to me yesterday in my 500SEC. It did it while I was doing about 60mph and a couple more times when slowing down. The speedometer started to drop and the car lost all power. Would you say your issue was the same?

[@markdietiker6870]

This video nailed my MB-560's issue perfectly. Great job and thanks for posting!!! I ordered a new relay, and while waiting for the new one to arrive, I decided to touch up the existing relay's circuit board solder. That fixed the relay and I'm still driving with the one that I refreshed the solder.

[@straybenzes]

Great job, Mark. Amazingly a lot of electrical gremlins in electrical components is related to cracked old solder joints. All the best.

[@nehuge]

Thanks so much for your videos! It keeps these cars from gettin junked.

[@straybenzes]

Awesome! Hoping that you can keep them on the road. All the best.

[@Engineerboy100]

Thank you, a lot of information crammed into a short amount of time. Well done! Good job man, thanks for posting!

[@straybenzes]

Thanks!

[@josh_blsoo]

This is exactly what happened to my car just now, thank you for this awesome helpful info.

[@straybenzes]

Thanks and good luck!

[@RJT-hp8vk]

Thank you, Sir. Happy new year to you and your family. I have a 1987 560 SEL original owner. You described my car’s problems with hi idle, tough starts, a/c problems stalls while driving. You are a genius. Thank you

[@straybenzes]

The best of luck troubleshooting!

[@raym7441]

Man, this is the exact problem i have been dealing with word for word on my 1990 300E 3.0L. Thank you so much for this video! I already ordered a new aftermarket Fuel pump relay and I'll update my post on the results!

[@straybenzes]

Nice result. Great job.

[@wolfgangkaminski4580]

Thank you for all explanations.

[@straybenzes]

Glad it helped!

[@jamesravelas5214]

You answered my question!! Thank you!!!

[@straybenzes]

Glad it worked for you. Good luck.

[@nadk8886]

Great video thank for uploading. This should solve my problem 😀

[@straybenzes]

Thanks. Good luck.

[@jimmycarter9099]

I always enjoy your videos 😊hope you had a happy 4 th I bought one off line turn out cheap I ended up puting the one I got from the junkyard back in so far so good😊

[@straybenzes]

You lucked out. They are very difficult to come by anymore.

[@padelistsilipanis3269]

GOD BLESS YOU MR STRAY BENZES LOVE FROM HELLAS PATRAS CITY

[@straybenzes]

Thank you!

[@BlownCapeTown]

My 300TE (1993) has had these exact issues lately! My mechanic has replaced both fuel pumps, Distributor cap, rubber cap part under air intake, full service and the car is running fine but then drops off power while driving. We've done leak tests to no avail and I'm at a loss, which is why I found your video! Nobody I've spoken to so far has even suggested this FPR might be the problem...Here's to Monday's parts mission, I hope? Also had kick down issues & Aircon doesn't work (might just need gassing, I don't use my aircon). Fingers crossed!

[@straybenzes]

The best of luck to you!

[@futurechurchofgodministrie9095]

Thanks for the video. I will purchase a new fuel pump and filter. If that fixes the problem, then I'm thankful. If not, I will purchase a fuel pump relay. Thanks for the info!

[@straybenzes]

Good luck!

[@asherjones1]

thank you so much the exact thing happened to me!

[@straybenzes]

Scary, huh? It is not for the faint of heart when the car engine just totally quits.

[@kosiekoos9408]

Great tip thank u

[@straybenzes]

Glad it helped

[@walidawhida9809]

هذا مانتمناه يارجل هو الترجمه بالعربي 😂 أنت رائع في الشرح متابعك من ليبيا

[@straybenzes]

شكرا لك ونتمنى لك حظا سعيدا.

[@johnbowerbank6890]

Thanks for the info I have a 1999 Mercedes-Benz SL500 I replaced the fuel pump and the fuel filter and when the car runs great but when it warms up and I turn the engine off I have to wait till the car cools down to start the car back up again so I'm going to replace the fuel relay and see if it's the problem thanks again have a great day

[@straybenzes]

It could be that little green relay, but I actually doubt it as an electrical issue is typically rather erratic and independent of engine temp. If this happens consistently with a warm engine it could still be fuel pump and / or fuel filter. Especially if you used non Benz parts. I have had both fail internally with the fuel filter causing starting and running issues. Good luck.

[@Ihavetruth22]

resoldered mine. feels better.

[@straybenzes]

Cool. That does indeed work sometimes.

[@sophiathe380sl]

Thanks for the video. Can this relay cause warm start issues? I’ve been chasing my warm start issue for a while.

[@straybenzes]

It could be, but I think that is highly improbable. Hot start issues are usually caused by low fuel pressure and that is usually due to an internally leaking fuel pressure accumulator. Did you change that one? That part sits right next to the fuel distributor on the driver's side. www.pelicanparts.com/More_Info/0004761021.htm?pn=000-476-10-21-M253&gclid=CjwKCAiAsYyRBhACEiwAkJFKotmqdMUDvinAuGKHfafQWnrvK49ra-z4REAv3YH8Wzdw8ngRyWKwWxoCDzwQAvD_BwE

[@sophiathe380sl]

@@straybenzes thank you. Yes, I changed the accumulator and it worked about 6 months ago. The problem is back. I changed the injectors but didn’t seem to fix it. Could it be the fuel pressure regulator?? I think it’s time to get my mechanic to check the fuel pressure.

[@straybenzes]

@@sophiathe380sl Yeah, that would be a good start if you cannot work on this yourself; Good luck!

[@TuanNguyen-pp4uo]

Can you please give a diagram to jump it.

[@chiefrocka8604]

Mine started doing it Brand new pump fitted 2 years earlier and occasionally it’d not prime the pump Got boring as mine was a Cosworth the most rare relay Once working it’d run like a champ though, still good cars a w2o1

[@straybenzes]

Really nice car!

[@ap6878]

Thx

[@straybenzes]

Any time

[@ImpalamansGarage]

Can they be rebuilt or repaired? Sounds like something one would want to keep on hand in the glove compartment.

[@straybenzes]

They are unfortunately a lot smaller than for instance the cruise control amplifier. They have only few items that I could see that could possibly be replaced. Good idea to keep one in the car when you need it In a pinch a jumper will work as well, but that is certainly more messing around that can be avoided by having a new one handy.

[@jammiejohnson1778]

I believe this may be the issue im having in my 2015 Mercedes Benz i have replaced the pump n filter and still getting those problems so i think that may be it. I get the part today

[@straybenzes]

Maybe or maybe not. That is a fairly new car model and there is no comparison between yours and these really old cars.

[@mkmk4314]

Hello I hope you're doing well,I was driving my 1989 Mercedes Benz 300se and just shut off but managed to pull off the road and again started but I had to keep my foot on the gas pedal because without doing so it couldn't idle until I reached home and parked it. Do you think I should replace the fuel pump relay? Please reply thank you

[@straybenzes]

Issues with the relay cause for the engine to run one minute and then to shut off completely and no pushing of the pedal will keep the engine running. It will not even start unless the relay comes back to "life". Your issue may be related to a few other issues that you will need to hunt down. Changing out the relay will not hurt and you will have instant confirmation if that was the issue.

[@bikeman123]

It'll hurt you wallet. A FP relay is £160!

[@MrMundaa]

89 420I SEL RUNNIG GOOD THANKS TO YOU AFTER DRIVING A WHILE PUTBIN PARK IDLING TO HIGH how do i turn it down in simple terms thankyou

[@straybenzes]

Check OVP for proper function, check the idle control valve at around 5 Volts it should be closed, check the throttle position sensor for proper function, and make sure that you do not have any vacuum leaks. Too much to go over in text answers and doing this remotely is really difficult.

[@daveg3493]

would spraying the relay with CRC Freeze-Off Super Penetrant be a good test

[@straybenzes]

Sorry, I am not familiar with that spray., but I am a little pessimistic that this will anything.

[@MrMundaa]

I HAVE QUESTION WIPER MOTOR WORKING IS THERE SUPPOSE TO BE WASHER ON BOTTOM TOP DO THEY HAVE TO BE TIGHT

[@straybenzes]

Are you referring to the wiper arms? There is a washer under the center mouning nut and yes, they have to be tight.

[@69oakfan]

I have a 1987 420 sel... It's been sitting in the garage for A while.. Haven't started it in about a Year-ish... Went to start it I didn't hear the buzz of the fuel pump when you turn the key... It was just a dry spin no fuel whatsoever... Not even a cough.. Will the fuel pump relay from a 1990 560SEL fit in my 420?... I have a 1990 560SEL parts car.. thanks

[@straybenzes]

The relay should be the same. Trouble is that the parts car's relay may not be in much better shape. Good luck.

[@69oakfan]

@@straybenzes Thank you appreciate it

[@robertbuczek3985]

Hi..if feul pomp relay is not working properly ,should be power on fuses ? i dont have electric power on 8 fuses and also on feul pomps...engene cant start...Thanks for same information where is problem...

[@straybenzes]

Make sure that the fuse(s) in the overload protection relay are ok. With that checked I would take out the fuel pump relay and put a jumper between pin 7 and 8. That turns on the fuel pumps. You should have 12VDC on pin 7 with the ignition on. Hoping this will help

[@fistteam]

Does anyone know what the Part # is for an aftermarket FP Relay? I have an ‘84 380SL that won’t start and has been sitting for many years (IKR!?!) 😅

[@straybenzes]

Try this one: www.partsgeek.com/catalog/1983/mercedes/380sel/body_electrical/fuel_pump_relay.html Sitting is the worst for these cars. You may have some more "fun" with other fuel and fuel injection related parts.

[@GMPLDR]

Also is the ac compressor relay and fuel relay the same?

[@straybenzes]

No, they are two separate components.

[@kalfoogaltmimi5043]

Hello, I have spark plug number five that is not working, even though I changed the wires of the spark plug and the spark plug, and I also repaired the gasoline distributor, and I also changed the injector, which connects electricity to the spark plug, but there is no change in the operation of the engine, meaning that the engine is running on seven speeds. What is the problem?

[@straybenzes]

Did you figure this issue out?

[@OK-qj5yg]

What is the part number of fuel pump relay for w126 560 sel ?

[@straybenzes]

Here is one from Peach Parts: www.pelicanparts.com/More_Info/0035452505A.htm?pn=003-545-25-05-A-INT

[@12dougreed]

Thanks for the video, maybe you could solve my problem, w202 m111 engine. Starts with long cranking ( cold in the morning) after that it's ok Park for half an hour, takes a long crank again

[@straybenzes]

Go to the trunk and gain access to the fuel pump relay )small cube looking thing to the upper right of the spare tire with a 30 Amp fuse). Have someone turn on the ignition and listen if the relay "clicks". You should also hear the fuel pump humming. Second thing to do is using some starter fluid and squirting it into the intake (remove the plastic intake pipe). Turn over the engine. If it starts right away it it most likely the fuel pump that needs replacing.

[@12dougreed]

@@straybenzes thanks 🙏 will do

[@straybenzes]

@@12dougreed Good luck.

[@foreverlivin3930]

Hoping someone can help me, I have a 2008 E350 Mercedes, it has extended crank, I have replaced fuel filter, fuel pump, crankshaft sensor,cam shaft sensor, cam shaft magnets, MAF sensor, Coolant temp sensor, and I still can not find what’s causing the extended crank. Car has no check engine light, and runs great. Also I have replaced the fuel pump 2 times in the last 6 months for some reason it has given out.

[@straybenzes]

Do you have a code reader? That is where I would start. Mind you that any codes represent just raw data as very often they hide the actual root cause, but they give you a starting point where to look without throwing money at replacing stuff. That usually introduces new variables and further complicate the failure search.

[@L4WNY..]

This happened to me yesterday. Just had a mobile mechanic come out (£358 later) said its 99% the actual fuel pump and not the relay?! Now I'm questioning their judgement!

[@straybenzes]

Jump 30 and 87 of the fuel pump relay and the pumps will continuously run. If your car runs the pumps are ok and it is the relay that is bad.

[@poisondaddy]

Can this be linked to the car only starting on neutral? For some reason my car can only be started on neutral and not in park.

[@straybenzes]

That sounds like the lever position switch mounted on the left side of the transmission is either out of alignment or it is defective. That would be my best guess at least.

[@dreway4161]

Natural safety switch

[@vintage76vipergreenBeetle]

👍

[@straybenzes]

Thanks!

[@MrMundaa]

i cant find the connection for oxygen sensor under passenger carpet this is a german model cant find image any where where is it HELP

[@straybenzes]

You'll need a 10mm socket to remove the plastic footrest under the carpet mat on the passenger side and you will see it to your left in the footwell area. Just unplug and push the rubber grommet through.

[@bikeman123]

My car jerks violently when accelerating and the fuel pump gets noisy. No problem starting the car and it never cuts out. Ive changed the fuel pump and all ignition parts and the fuel pressure is good. I think the relay is fine.

[@straybenzes]

Hmm. That is difficult to diagnose from afar. What car model, engine, and transmission do you have?

[@DarrylBates]

Got a2005 C class Kompressor and driving today it just lost all power no fuel getting to fuel rail could it be the relay thankyou for your time

[@straybenzes]

@@DarrylBates You can check the relay and fuse. Should be behind a little cover on the driver side in the trunk (left upright wall). It's the top relay and the fuse should be the 4th one 30Amp. Found a video that covers troubleshooting the fuel pump pretty well: kzbin.info/www/bejne/iHK8oWuiZ7Zla5I Good luck!

[@Mnisimnisi]

Good day My car is E220 W124 im strangling to start it its been month's now and I cant find the problem , its cranking but no start only promising to start , I changed petrol pump still not start , and before when you go around it just goose off after sometimes it starts sometimes not starts ,please help

[@straybenzes]

That engine has electronic fuel injection and is thus completely different than the older KE Jetronic fuel injected engines. There are quite a few ways why your car won't start. Check the spark plugs after cranking. Are they wet with fuel or are they dry? If they are dry I would check the wiring harness and the connections between ECU and the injectors. If yours is a 1993 model chances are that you have wiring harness issues due to the known biodegradable wiring insulation that had been used around that time period. It could also be an issue with your ECU and / or OVP relay. Hoping this will help. Also, this is a fairly common issue so you may want to Google it.

[@Mnisimnisi]

@@straybenzes yes its 1994 model

[@straybenzes]

@@Mnisimnisi The best of luck!

[@serverdll]

hi sir, new suscriptor here. do you know something about 722.3xx gear boxes? mi w124 won't work very well. when i start to move the car 1st gear never come off to a 2nd gear, but if i quickly put N and D again 2nd gear gets in. then 3rd an 4th as ussual. i try to diagnose this by a year now. filter and oil are new, i work in car electronics and mechanics but old benzes are a little like black magic, no ones want to touch it. can you give me a cable with that one? thanks in advance

[@straybenzes]

Hi Patrick; What year and model is your car? The 722.3 is a very sturdy transmission. To me this sounds like a bad or stuck kick down switch. Look under your gas pedal and locate the kick down switch. Make sure that there is no carpet or foam material stuck there. Does that switch move freely in and back out? For the heck of it disconnect the wire connector to the switch and take a test drive. If your tranny shifts ok it is definitely the kick down switch. Good luck.

[@serverdll]

@@straybenzes thanks for quick response, pedal switch in perfect condition and solenoid cable already disconnected and tested with no change.

[@serverdll]

@@straybenzes car is w124 1990 M103 and 722.358 gearbox... 124.930 chassis.

[@straybenzes]

@@serverdll Got it.

[@straybenzes]

@@serverdll This also can be the auxiliary oil pump not working or not working properly. Potentially, it may be a blocked passage(s) in the valve block assembly.

[@waltermartinez5907]

back in the day you would open those and resolder everything nicely. Seems they have poor solder in many of the Mercedes relays. I've solder a couple that then lasted 15 years

[@straybenzes]

You are correct. I have saved some of the electrical parts by merely desoldering the solder joints on the boards.

[@MrMundaa]

HOW TO TURN IDLE DOWN? 1989 420 SEL

[@straybenzes]

You don't. This is the most misunderstood function of the KE Jetronic. You need to make sure that your idle mixture gets you the highest RPM and no stalls or surges. Then you tend to the overload protection relay, vacuum leaks, the throttle position sensor, the idle control valve, and I am sure I am forgetting a few items. There is no idle adjustment screw like in int golden days of carburetors.

[@Rossithailand]

Hi I have , e190 w201 1.8 it's slow to change gears 3 second pause, can anyone advise where I should start looking

[@straybenzes]

This can be a symptom of the modulator needing replacement, faulty vacuum level, or even debris built up in the tranny valve body. Checking the vacuum level and modulator are the easy check ups. Opening up the tranny is more complex.

[@Rossithailand]

@@straybenzes I think it might be the potentiometer now , but I will look at vacume when I get it up on the lift.

[@Rossithailand]

Thanks for fast reply, your videos are a great help

[@straybenzes]

@@Rossithailand I hope you will find the root cause.

[@straybenzes]

@@Rossithailand Glad they are helping.

[@MrMundaa]

WHAT IS HOLE ON TOP OF AIR FILTER FOR

[@straybenzes]

There should be a replacable cap in it, but that is for using a 3mm allen wrench to adjust the idle mixture.

[@shorecarul]

Could this be the problem on my 260e? Car is not revving above 2-3000 rpm

[@straybenzes]

The relay is unlikely the reason ofr the low revs upon acceleration. That is more likely due to the air fuel mixture being too lean. Check the main fuel injection and differential pressure first.

[@shorecarul]

Thanks for the reply! I had this issue since I bought the car, now I fitted an electronic fuel injection system and it behaves exactly the same....

[@straybenzes]

@@shorecarul yeah go back to the basics

[@shorecarul]

Will check the fuel pump and fuel screen in the tank, I'm running out of ideas lol

[@straybenzes]

good luck!@@shorecarul

[@tendaimutiro2243]

Hi All the way from Zimbabwe. What could be causing my baby c200 (202) to cut running just after starting and managing to drive if l put a rev then cut again as soon as l let off the acceleration paddle and allow it to get to below 5 revs reading on the counter, all this time my gauge will be correctly indicating 1/4 tank fuel

[@straybenzes]

Thanks for writing to me. That should have the 2L M111 4 cylinder engine in it. It has a completely different engine fuel and control system than the old KE Jetronic cars. As such it is best to first use a OBD 2 code reader to scan for any trouble codes so that you can narrow down your particular issue. It is very difficult fi not impossible to diagnose this from remote.

[@Devan_Bolin]

But fuel pump relay wld be a great video for the channel and it’s not a lot of work and wld help a lot of new owners

[@straybenzes]

Every little bit helps.

[@yousifyousif8659]

@@straybenzes well I have a question my car is 420 SEL I started and is don't start then I don't have fire in the spark place? What should I have to do???

[@straybenzes]

@@yousifyousif8659 Oh wow. That could have a variety of reasons. Are all spark plugs not getting power? Did you check the distributor cap and rotor for any issues? It could also be the EZL ignition module. How did you establish that you do not have any spark?

[@Devan_Bolin]

How bro man love the ch but if you cld show a video with a quick fix (when fuel pump relay goes out quick fix) I keep two wires copper thick you can use to bypass fuel relay but you can wire to ports 18. 31 something like that but you can keep fuel pump on but have to take positive Terminal off to cut off fuel pump but you can power your car with out a fuel pump relay and I know how to start a W-126 without a key which I want explain in comments but will give a hint if your steering lock isn’t Engaged it’s a screw in abutton to pull out the steering lock Assmley incase of key lose

[@straybenzes]

That is another couple of great tips. Thank you!

[@Neiman555]

Is this an expensive fix ?

[@straybenzes]

It can be - they are not esy to buy anymore.

[@GMPLDR]

Where to buy?

[@straybenzes]

Try the MB Classic Center or Ebay. I have not found another source for new ones for the V8 gas cars yet.

[@VILLEGAS76able]

Hahaha! This also happened to me. I changed out the fuel pump and saw this video, so changed two relays and magic, like a brand new car.

[@straybenzes]

Wow. That is a nice result.

[@MrMundaa]

MAKE THER WIPERS GO BACK AND FORTH

[@straybenzes]

Not sure what to make of this comment and were it belongs. Sorry.