Fuel Issue Perplexed

[Cherokee2072]

Please excuse me if I have missed a previous post or posted in the wrong section.

My bike is an 87 k75S.  Bought from a 10 year nap. 
I cleaned the fuel system, replaced all hoses. 
Air intake Hose, Air filter,  crankcase vent tube (checked throttle body tubes) replaced. 
Cleaned injectors (new O-rings).
New fuel pump, lines and filter.
New temp sensor.
Cleaned and verified air meter operating in spec with multimeter.
Adjusted TPS.

The bike started and ran great while on the lift.  Test drive in the driveway, zero issues, ran great all thru rpm range.  Finished buttoning up brakes, lines, tires etc. 

2 miles into first trip today it died.  No fuel pump.  No power to #6 fuse.  It blew the fuel pump relay. 

Looked over the harness, couldn’t find a short.    Replaced relay.  Started and ran but would stall out after a few minutes or upon revving over 3k.  Replaced the fuel pump suspecting a short in the pump had caused the relay to blow (had a spare).  Same issue. 

Has anyone had a similar issue?  I’ve been thru the troubleshooting chart thru the course of bringing it back from the grave.  Not sure where to double back or turn next.  Hopefully it’s something obvious that I’m just too tired to see.  Thanks in advance for your help!

[Cherokee2072]

To be honest I haven’t gotten that far into it.  No click made me suspect, replaced, click and start.  I assumed, as with a temperamental car I had in the past, that a short in the pump or harness caused it to go.  Or it could have been 34 years of age and and it was just it’s time to die.  I will dive in with the multi-meter and give you a more detailed diagnosis of why it no longer works, but alas it is no longer functional.  My hope was someone with more experience with The Jetronic system may have experienced a similar behavior in the past.

[John Lang]

Check that grounding points are clean (under tank central and transmission-to-battery). A dirty ignition switch could cause the intermittent symptoms you describe.

[Cherokee2072]

Grounds were cleaned as part of the general maintenance, the switch was not.  I saw the write-up in another post.  I will tackle that today and report back.  Thank you!

[Laitch]

I will dive in with the multi-meter . . .  My hope was someone with more experience with The Jetronic system may have experienced a similar behavior in the past.

You're describing symptoms that could be caused by several differing sources including the electronic control units themselves. Download the troubleshooting guide from Repair Guidance then run the ignition control unit and fuel injection control unit diagnostic tests.

[Cherokee2072]

Update

Cleaned/lubricated the switch, looked to have been done before as well.  No flickering or voltage fluctuations, also no change in symptoms.  Went back to the diagnostics.  I used this before when bringing the bike back from its sleep, very great tool.  Fuel pressure test shows initial pressure a little low 32psi and it drops off quickly to teens.  Opened the tank and I am getting a strong stream back into the tank from the FPR when the switch is turned on.  Much stronger than previously.  I suspect my pressure relief valve has stuck in open position creating an open loop.  Thanks for all of the input to date. 

[Laitch]

Thanks for the update.

[Cherokee2072]

Pulled the fuel rail just to verify all injectors firing as they should, they are.  Applied clamp to the outlet line on the rail to simulate regulator pressure and the bike started and revved pretty normally.  Ordering a new Pressure Regulator and will update the board later on.  Thanks again. 

[Cherokee2072]

***Update***
To begin at the beginning.  All rubber parts have been checked and what was suspect replaced to remove vacuum leaks from the equation.  I have rechecked the air flow sensor, temp sensor (new), fuel pump (new), FPR (new), plugs, and wires.  In going back thru Bert Vogel guide I found a disparity in the replacement pump relay I had and the original I replaced on the day I was stranded.  The location of the 30 and 86 blades are reversed.  My fault for not verifying more closely. The interesting thing is the bike starts and cranks with this relay, pump operated as it should coming on with the switch, but loses fuel pressure quickly.  So I pick up the 318i relay from NAPA today (Alternative List Replacement) verify it to the original, and when I plug in the new relay the clock resets and the fuel pump kicks on with key out and kill switch off?  The clock issue happened on the day of the initial relay failure when it died on the highway.  I have disassembled the switch and did not find any visible issues at all, clean and lights work well with no flickering.  The grounds under the tank and battery grounds have all been cleaned.  Possibly a wire in the loom from the key switch grounding out? 

[rbm]

Are you absolutely certain about the FI relay you replaced (BMW 318i).  Does your replacement have two 87 terminals and zero 87A terminals? To be precise, 30 is the common, and 87 is a normally open terminal.  87A is a normally closed terminal.  With the relay unpowered, there should be no continuity on any of the 87 terminals to pin 30.  With the relay energized, there will be continuity on both 87 terminals to pin 30.  Use an ohmmeter to verify this configuration.

This is what you are looking for:



Your symptoms indicate to me that your relay has an 87A pin that is routing constant power through Fuse 6 to the fuel pump.  That's why it's always on.

[daveson]

Another thought, since the wrong relay didn't turn the pump on,  the previous owner may have swapped the wires to suit. Therefore the correct relay turns the pump on without the key if 85 has earth without the key,  which I doubt) Check that the red and green/yellow wires have not been swapped.

The wrong relay should work I think,  but put extra load on the kill switch, which should be beefy enough to cope anyway.

Does the fuel relay really effect the clock? How? I don't think it should.

What's the relay part number?  I think it should be 61.36-8 373 700, with a light green cover.

[Cherokee2072]

The relay that stopped working originally was the OEM part from 1986.  So the OEM wiring wasn’t fussed with.  Verifying the continuity of the replacement relay.  If that is correct I will keep looking for an open/unwanted ground. Next step is to order a relay from EME and wait it out. I have had luck using the alternate parts list and NAPA up til now, but this experience has me going back to an OEM only slant for electrical replacements.  The clock part has me scratching my head.  It happened the day it quit.  I chalked it up to pulling fuses and relays trying to make sure nothing had wiggled loose.  Now I’m fairly sure it is associated with this relay or a related ground issue somehow. Thanks again for all the assistance. 

[rbm]

Air horn relays have this configuration. 

[Cherokee2072]

RBM you were correct.  The Napa part 318i relay purchased does have an 87a.  Purchasing a relay from EME, still working on finding a possible ground issue as I believe that may have caused my initial problem and I don’t want to be stranded again, thanks for the great advice. 

[Cherokee2072]

Too late after a long day, I mis read at first. I am clear in your thought process now.  I did check the old relay, I don’t believe it will be coming back to life.  Will go through the wiring while I wait for a new one to make its way out to me.  Thanks again. 

[Cherokee2072]

Oh, I had been working backward based off the troubleshooting page from the workshop section since day 1...

[rbm]

TMG: The horn and load shed are standard 4-pin 1 Form A auto relays and can be swapped.  The FI relay is a 5-pin 2 Form A auto relay and has no equivalent in the relay box.

[Cherokee2072]

👍.  Again, thank you for your time and input.  Much appreciated!

[rbm]

Cherokee: The clock probably reset when the system got loaded down plugging in the relays live.  That plugging action might have pulled the power down towards 0 volts for a few milliseconds (brown-out).  The clock will reset if the reset pin on the clock IC is grounded which might have happened with the brown-out. You can simulate this by pulling fuse 3 for just a second; time will reset.

[daveson]

Prob not a short, no fuse blew. Possibly just weak power. Check the wiring is fully pushed home on the relays socket. Clean and solid. If loose it could lose contact on a bump for example. With the relay removed, push on the sockets in the relay holder with a small screwdriver to see that they are tight, and don't move down. Or wiggle the wiring, or look for a weak spot.

I probably shouldn't say this, but if you bridged both 87 sockets with a wire, you might be able to use the horn relay, just as a temporary testing measure.

[rbm]

I probably shouldn't say this, but if you bridged both 87 sockets with a wire, you might be able to use the horn relay, just as a temporary testing measure.

Mmmmm, maybe not ... Ampere rating on the relay contact may or may not be large enough to take the current draw.

[daveson]

True, hopefully just a loose connector to clip back in, and nothing wrong with the first fuel injection relay.

[volador]

Too many ex-hippys on this site

Amazon Lime FI Relay



FI relay 5blade 61368373700

Load shed 4blade 61311459677   Relay, K75 - K1100LT; R80R - R100MYS. This relay is assigned to multiple uses.

Including: fan, starting load shed, horn, Motronic, and fuel pump on selective models.

[Cherokee2072]

So to confuse me further, my repair manual says the FI is the far right relay.  Anyway, is swapped the right relays this morning with no change, so both are functional.  Fuel pump still kicks on, horn still works on either.  So the load shed is what was causing the pump to be non-op or full on. 

[Cherokee2072]

And I did verify all connectors are clean and tight, wiring good in the box.