Randy V

Good to know - thanks, BC.

dr bob

Randy--

Check for voltage on both sides of the fuse once the relay is jumpered. Current for the fuel pump is on a dedicated feeder from the battery plus side. A loose or corroded connection in the battery well will keep power from the FP relay.

So--

-- Check/clean/verify the minor wire connections on the battery positive terminal.

-- Check/verify that you have +12 battery voltage at the 30 terminal on the fuel pump relay socket. (Enters at CE terminal U21) If no voltage, go back to first step.

-- Install the FP relay jumper between 30 and 87 in the FP relay socket. Verify that you have +12 battery voltage at both 30 and 87, where the jumper is plugged in. If no on 30, go back to first step. If yes on 30 but no on 87, fix your jumper.

-- With battery voltage on 87, pump should be running. If pump is not running, pull the jumper, and pull the fuel pump cover. Plug your meter positive into the pigtail for the pump. Replace the relay jumper. Should have +12V battery voltage at the pump pigtail. If yes but no pump run, pump is likely failed.

-- If no voltage at pump pigtail, look for voltage on both sides of FP fuse 38 (still installed) with relay jumper still installed. You should see +12 battery voltage on both sides. If one side only has voltage, fuse has failed. If neither has voltage, check between relay and fuse socket for a break.

-- If both sides of the fuse have voltage, check for voltage at CE panel U25. Should be +12V battery. If no voltage at U25, look at the fuse again, and at the fuse socket connector underneath. If voltage at U25 but none at the fuel pump pigtail, you have a wire failure or the U25 connector to CE is bad.


This should tell you all about the power supply side of the fuel pump circuitry.

Mrmerlin

Nice writeup Dr Bob

neilh

Good write up, Dr Bob, I tend to leave out the steps to achieve the result :-)
I was trying earlier in the thread to determine if Randy has 12V at both ends of the fuses, and as you surmise, if Fuse 38 has +12v, then U25 and the harness needs to be checked out.

rbrtmchl

EZK is a German acronym for ignition with a knock sensor. And, from the New Visitor FAQ, LH is Luft Heiss = Air Hot (hot wire air flow meter system).

AO

OH SNAP!

Randy got pwn3d!

Randy V

Thanks, sir.

I saw LH in there but not EZK.

I've added it to the acronym list.




Thanks, Bob - I'll get this to my guy.





Any guidance on how to check/disable the imobilizer circuit to rule it out as a cause?

dr bob

Randy--

Easiest way is to lock and then unlock the car from the driver's door with the long (non-valet) key. Disconnnecting the battery for a bit will cause a full reset of that system also.


The troubleshooting steps I shared are independent of the alar/immobilizer.

Randy V

Thanks, Dr. B.

I found a previous post by Alan where he describes disabling the imobilizer function but I'm not completely clear on what and where the leads are located:

WallyP

Look at the bottom of the Central Electric Panel. Plugs are alpha left-to-right, with no i plug. N should be 13 from the left, Q should be 16 from the left.

Terminals are arranged:

15 25
14 24
13 23
12 22
11 21

So, as Alan says, N11 is bottom left terminal on the 13th plug (they are identified - use a flashlight). Q12 is 2nd up on left on the 16th plug.

Randy V

Thanks, Wally - that helps.

I sent my guy your write-up Bob and he followed it specifically - like I told him to. He was getting off on multiple tangents.

Following your troubleshooting procedure he determined that fuse 38 was bad, although it looked fine. Inspecting that fuse was one of the quick-and-easy things I looked at while waiting for the tow truck to show up.

I had directed him to do that yesterday but your directions let him to the correct solution. Car starts and runs fine once again.

Thanks, sir and to everyone else who provided assistance.

Except Andrew.

the flyin' scotsman

Randy.........you'll have to excuse Andrew, he slipped and sprained his ankle

Glad you found the blown fuse but what caused it to blow?

dr bob

I'll keep an eye on the mailbox for the bonus check.


Glad it helped, and thanks for the feedback. Too often troubleshooting is less than methodical, making the results less than reliable. Usually it's the simplest stupidest stuff, while we go looking for the most exotic expensive causes first.

-----

You'll still want to figure out why the fuse blew. Possible it was mechanical failure of the fuse itself, but that's really unlikely. It may be that the pump is on the edge of failing, and this is just a little telltale heads-up warning of bigger things to come. In my collection of diagnostic tools, I have a pair of pigtails for the amp meter that lets me plug into a fuse panel or a relay socket. You can also do a resistance measurement through the fuse and look at voltage drop to figure out the current passing through the fuse. Either way you can see if the running current on the pump is really getting close to the fuse's rating. If it is, start pump shopping now and plan on pump installation sometime just before you go shopping for fuel again whil ethe tank is at min level.

borland

Since fuse 38 also protects the O2 sensor heating circuit, that might be the real source of excessive current draw.

Does your mechanic pay for any future towing fees related to his so called 'repair'? If it was my car, would surely want to know why the fuse went bad.

AO