• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

740 86" 740 Ti stalled out. No spark.

Acid8000

Acid8000

New member
Joined
May 3, 2005
Location
Victoria, BC - Canada
Had to get her towed like 300km. Was not pleasant.. But she's home at least. Uhhh.. wondering if the throttle position sensor can cause no spark? Or would that just be the cam position sensor or crank position if it has one? Reason I ask about the TPS is the car was seeming to act up the last few days before dieing. The revs would rise to 1500-2000 while you were at a stop or something. Would rise then fall, rise.. then fall. And the few days before that I was cleaning around the and inside the throttle body with intake cleaner and some rags. She's automatic. Unfortunetly...

The wiring harness is rotten pretty good. Wondering when that's actually gonna start affecting stuff cuz as is the car drives fine. I've only just got her. I'm in about 2,400kms into the car now . She's got a heck of mileage at 430,00kms. But I gave her a compression test and she was good across the board except lil high near the back cylinders.
 
86 has a Hall sensor, not a cps. Those do have wiring probs sometimes. That year also has rotting harness as you say, and yes that can be a problem, and may be yours now. Dave Barton used to sell good harnesses, some remake it with new wire.

Idle can be bad idle motor or again the wiring. Check BB FAQ for how-to on a fix.
 
K so little troubleshooting and noticed the fuel pumps don't come on when trying to crank or to prime. So that's a more clear sign of hall sensor correct? I'm pretty sure I'm just gonna get a whole new assembly.

But while I'm waiting for the part to arrive in the mail in gonna do some repairs on the wiring harness. Do you guys think it's easier to fix it in the car or do I try to remove the engine wiring harness. I'm wondering if I undo the main clip in the passenger area above the turbo. And follow those wires checking them as I go. Should hopefully find and fix .
 
Acid8000 said:
K so little troubleshooting and noticed the fuel pumps don't come on when trying to crank or to prime. So that's a more clear sign of hall sensor correct? I'm pretty sure I'm just gonna get a whole new assembly.

But while I'm waiting for the part to arrive in the mail in gonna do some repairs on the wiring harness. Do you guys think it's easier to fix it in the car or do I try to remove the engine wiring harness. I'm wondering if I undo the main clip in the passenger area above the turbo. And follow those wires checking them as I go. Should hopefully find and fix .
Click to expand...

100% pull the harness. It'll probably fall apart as you do it if it's original to the car.
 
K,. My last question was more. If i unplug that main plug above the turbo/ right beside the coil . Can i remove the harmess after that or does it connect back up on the other side of the engine bay? I see 2 other main blocks kinda. But I'm pretty sure one of those is headlights & accessories. And the other ... something..
 
Your car should have a charge air over-pressure switch. On my 88 765 this switch had poor wiring connections. This switch completes the ground circuit between LH2.2 ECM and the fuel pump relay. It's job is to cut off the fuel pumps and injectors if the boost pressure gets higher than a certain spec.
 
Wiggle test the harness and see if it stalls or changes rpm.


I would definitely swap out the harness as preventative maintenance, but don't be surprised it it's not the final solution.

I would also wiggle test the hall sensor wiring and see if it stalls. Clean up all oil leaks back there too.
 
Well I'm ordering a whole new dizzy assembly
Just gonna attempt to remove and repair the harness before the part arrives. Pretty sure I'm gonna have to remove the intake mani too but that's fine I've got a spare intake mani gasket. Gonna get the injectors tested and cleaned while there out too.
 
It's always worth pulling the intake on these every so often and inspecting or cleaning the PCV components and degreasing the engine and wiring and hoses down there as much as possible. Inspect for bad wiring, make sure all terminals are seated in the connectors well, check for torn IAC hoses, fix torn vacuum hoses, clean the intake off and the t body, etc.

On any hall sensor 740, the sensor wiring always degrades fro. Heat and oil contamination. It's also always been close to impossible to find a good used hall sensor that isn't cracked and dangling, so I'm glad aftermarket ones are still available.

Just label the connectors while down there, because they aren't idiot proof and I smoked a ECT sensor once, literally, when I plugged a cold start injector connector into it incorrectly. Right when I turned the ignition on, POOF!!!
 
Hah. Yeah nothing worse then damaging something yourself. Then you have no one else to blame! I yeah
. Exactly what you said. This car Was needing to have the manifold off anyway to do some good spring cleaning under the manifold.

Yeah my car has really bad wiring disintegrating around the ignition coil, uhh the cruise control module has it bad too. And the headlights wires. Good old 80's biodegradable wiring!
 
Pull the manifold to examine, clean, and access things.

Cut into the wiring harness (carefully) to see if / where the wiring has deteriorated, then repair what needs to be repaired, and when done cover the new wiring with good electrical tape.

Not as good as a new harness, but worth a try: it worked for me on my '86 744 Turbo.
 
Yeah. I have the harness out now, much nicer to work on in the garage. The harness is in such a **** state.. Can't believe the car was still running fine with everything in a state like this. So many bare wires beside each other.

Uhh, the wires going to the hall sensor. Can they be fixed? It looks like 3 wires running throu 1 case almost. I seen a couple cracks along the casing and some bare wires showing throu
 
Acid8000 said:
Yeah. I have the harness out now, much nicer to work on in the garage. The harness is in such a **** state.. Can't believe the car was still running fine with everything in a state like this. So many bare wires beside each other.

Uhh, the wires going to the hall sensor. Can they be fixed? It looks like 3 wires running throu 1 case almost. I seen a couple cracks along the casing and some bare wires showing throu
Click to expand...

I coated my bare Hall wires with liquid electrical tape,
 
I haven't looked at too closely yet but I think the hall sensor is 2 wires on the inside with the ground running outside of those but still within the outside sheath. Il fix her up regardless of how shes orientated!
 
You must log in or register to reply here.
Back
Top