mark kibort

After a good practice session and the brake problems getting much better (Sears is a slower top speed track vs Laguna and the brake pads are now doing their job and rotors actually look better w much less grooving)
More on that later
The qualifying session was going well as I was runng w Darrell Anderson in his super fast t1 mustang and down the carocel the car just dies
I run to the dragstrip way off track.
It wants to start but can't so it has spark
Feels like skipped tooth timing belt

I pull the covers but all is well
Then spend the next 3 hours chasing it electrically
Fuel pump not getting power
Rely is good and jumping it doesn't get the pump going
However putting power to the pump at the pump works!!
Can it be a bad wire going to pump ?
Checking that this morning
Hot wired the pump w 5 mins before race and got 3 fun laps before the rigged connection broke
Uggggg
Fixed it while in car on drag strip again and got to hotpits where some angel helped secure it
2 turnes out of pits and transmission locks in 3rd gear
Uggggg
So I beat the car silly for 15 mins at the rev limiter !!!
( sorry Greg no oiling issue here!!!!)
Thoughts on fuel pump issue??????
Cooked wire leading from pin 87 to lower wires that go to the pump ?

mark kibort

Uggg

jcorenman

Is the fuse OK? If so then most likely a cooked wire or terminal.

Start at the CE panel and inspect the #87 relay contact-- if it was corroded or loose then it will heat up and burn. Same for the fuse terminals-- relay #87 connects directly to the fuse (#42 on an '87, I think that's what your chassis is).

Then trace the 2.5 red/green wire from the other side of the fuse into the harness (connector U5 on a '87), check the harness for any damaged spots, and check it where it comes out in the rear.

Stock pump? Stock fuse?

AirtekHVAC

Dang mark...sorry to hear about the problems...like following you adventures.

mark kibort

Ugg!! There's a fuze for the pump??
I bet that's it
Getting to the track right now
Got to pull the transmission and free up the 3-4th gear lock up
Then if it's just fuse
That will be great !!!

mark kibort

Fuse 42
Missed it uggggggggg
Cost me some fun but ran half the race in3rdanyway
Now unlocking the trannie

jcorenman

Good, one down.

No fuse for the tranny. Good luck, I hope it is simple.

mark kibort

That's funny! anyway, AHHHHHHHH
I should have learned my lesson with the clutch issue.. remember, thought it was fixed and you guys said, you fixed the effect, not the symptom?????? what more obvious than a fuel pump fuse being blown to say, " HEY IDIOT, there is something wrong , OTHER than the pump! "
needless to say, 1 lap on qualifying, it blows again. I put a new one in that I had In my pocket. blew in the hot lap, so no qualifying. start from the back...... spend a few hours running a new cable from power , new fuse, and to the fuel pump, ignition activated.......... DUMMMY again, didn't think to disconnect the stock fuel pump power connection, because I had the stock fuse removed. dumb dumb...... There is a short !! I blow the fuse on turn 2 at full tilt, high g loading and very bumpy! The short is still there if the fuel pump power line has a wire going to it and it goes to the short. Now that I have a new power connection, the new power connection new has access to the short too!!!! AHHHHH. it blows in lap 2 of the race , after passing half the field and getting in the groove! oh well. my own fault ... that was a little obvious, but now need to find that short. don't even know where those wires go to from the pump. have to track the wire bundle down.. well, long wait until laguna in sept to fix it.

hinchcliffe

Grounding O2 sensor but I'd imagine your exhaust is all different, haven't fully followed your adventures in a while? Had that in mine and it kept blowing the fuse but would run jumpered.

Rob Edwards

Maybe you oughta haul that thing to Sharktoberfest and there can be a tech session on the do's and don'ts of race car prep.

Mark Anderson

Mark I may be getting a 1989 GT trans in late this week

mark kibort

That's interesting. as you might know, I have a tap on the 02 sensor wire, for the AFR , but the o2 sensor wires are pretty isolated. it seems to be working, so the 02 sensor isn't melted and shorted. that would make sense. But , if the fuse is blown, wouldn't that disable the o2 sensor output?... remember, I still had the original ciruit connected, so maybe I was backdriving it from the fuel pump positive connection. . got a few more things to look at, so thanks. time to break out the electrical drawings!

dr bob

Mark, it's the heater circuit for the O2 sensor that shares with the fuel pump. Two white wires in the oxy sensor cable. One should be grounded, the other is battery voltage when the pump relay is closed.

mark kibort

Thanks!
Keep in mind, this is intermittent. only when going full out down turn 2 at sears. otherwise, everything works well. current is 7amps, regardless of throttle, but only was able to test it around some service roads.
the O2 sensor wires look very open and free. rubber grommet is in place at the chassis entrance.
the wire to the pump from the fuse panel connection is solid. (red/green wire)
could the pump have some kind of high current draw under full throttle ( I think unlikely, due to the pump always keeping 50psi (ish), it doesn't know if the fuel is going to engine or into the tank return.
what if the fuel filter is clogged.. (also unlikely)

I guess the only likely guess here is that the o2 sensor as it is getting cooked at WOT, shorts out? maybe the fuel pump is shorting out?

any guesses welcome. Ive been starting at the wiring diagram and wiggling wires, doing continuity tests and ohm measuring for hours. nothing looks out of the ordinary. this kind of intermittent problem is so hard to find.

tmpusfugit

Just a passing thought, but speaking for myself, I would replace the entire wiring harness in a 928 if I were to go racing. Why? As a starter, the stock wiring harness weighs about 43 pounds in total. Secondly, the wiring 928 harness(s) I have been into, have all had corrosion in strange places, broken wires here and there, a bunch of unnecessary wiring for racing, on and on. Companies like Painless or Watson Street Products make some very robust kits for wiring race cars, or anything else. This would yield modern wires and modern connectors, of the necessary current capacity, while eliminating the entire CE panel. The tough part of the process would be connecting the computer(s) as I don't think there are modern connectors to readily / directly replace those connections. Those would require careful dis assembly of the old connector, removal of the old pins, finding the correct replacement pins, connecting new wires to the new pins, and then putting them in the old connector "blocks". Not rocket science. I have done it more than once in old electronics, some dating back to WWII or older. But, when finished, many of the electrical issues we have with 928's should be minimized if not eliminated. Not sure I would try this with a street car where I wanted to maintain all the various functions and features, but for a race car it could be made far more simple and most likely far more reliable. I have done this on several cars, admittedly all were more simple electrically speaking than a 928, but it is pain quickly forgotten when done...