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1988 740Turbo Stalling issues

thelostartof

unbalanced chemical
300+ Club
Joined
Jun 26, 2002
Location
Apache Junction, AZ
LH2.2, 745Turbo 1988.

Problem is the car will stall at random (much more so once hot). When Cool (100deg out here in AZ) it ran for around 4-5 miles without any issues, no stall or random hiccup or bump. After that point once warm it starts to just drop out RPM at random, sometimes it will restart right away first time, othertimes it will crank and crank and restart when it wants to.

We have tested 4 different Powerstages and they all seem to act the same way.

We have reflowed the FP relay as it had some cracked joints, swapped out the intank pump as the stock one would not power up when jumped, the 850R pump that we installed now powers up along with the main pump when you jump it. With the relay it also powers up now.

We have tried 3 different AMM's with the same result.

The Hall sensor in the distributor looks fairly new, and has a reman bosch sticker on the cap. On the inside we found there to be some odd pieces of black plastic loose inside of it, we removed those and the issue was the same. Since then we also took another Hall Sensor Distributor off a local 780 that had last run without any issues. This unit acted 100% the same as the one that came off the car.

We had to cut to splice in a new connector for the Hall sensor wiring, I crimped it the first time but after more issues we figured why not and solderd them so they should have a good connection now one would hope.

We also tested their ignition coil out and it tests out to spec with around 1ohm betweene 1 and 15 (spec is 1.2+/-.2), and between 1 and the main it reads 9k (spec is 9000 +/- 800).

Car has new plugs and cap and rotor along with bosch wires.

Did a cold (100deg outside) compression test and it came out to 120-110-150-150.

When the car runs it runs good, but besides that it has this random RPM drop out and stall that we can not figure out.

Any other ideas on what to test besides throwing more $ in new parts at it?

I might have a spare fuel ECU here but besides that nothing.

Trying to get these guys going so they can make it back to Texas.
 
Have not tried that yet, so completely bypass the Fuel Pump Relay?

No love on the coil it sounds like Mike?

FYI, LH2.2 doesn't prime like 2.4 does, but the pump should kick on while cranking. Ran into that on a local's car.

Any chance you can toss a spare ecu and icu at it? I know you do more 2.4 stuff. There really isn't much else to it that would be temp sensitive like that.

Maybe check the ECT at both the ECU and ICU connectors when it's warm to make sure it's not going haywire.

Knock sensor tight to the block?

Metal fuel tank sender right? Check the crimped ground on the sender itself. Had some funky stuff on mine and ended up with a tow thinking a pump died a couple times before I stumbled upon that one.

Still thinking, but running out of ideas...

We just threw in another 541 ECU that I found in my shed, for whatever reason it was idling around 1500rpm now, did an almost stall and then kept back up to 1300 so they are going for a test drive to see how it runs.

I am going to swap back on the Reman Distributor that was on here as it looked to be in much better shape (tho oddly enough it was missing bolt orings, for the seal into the head and on the shaft to hold it in place inside of the Cam, I threw on some spares that I had on one of mine.

I have not tested the ECT but I would expect that to be a rich condition and other issues not just a full rpm drop out. Besides buying a new Ignition Powerstage and coil and trying those no idea what to test or check next. I am going to order new of those but that will be a few days to week to get here as I do not feel like paying extra $$ for off brand parts today.

The ignition coil off my 744 tests 10500ohm between 1 and main and ran just as bad as before on theirs, the only other spare coil I have test out at 11000.

If this doesn't work then the guys are just going to catch a plane back home and this car will be sitting in my backyard until I can get it figured out so they can drive it back to Texas.

So while this quad headlight front end is growing on me I so do not need another thing to try to make sense of and fix.
 
Sounds like a case for cartalk on NPR.

But seriously. Does it still only stall on an "emptier" tank or does fuel level have no influence? Does it matter if its hot or cold outside?
 
Sounds like a case for cartalk on NPR.

But seriously. Does it still only stall on an "emptier" tank or does fuel level have no influence? Does it matter if its hot or cold outside?

It has 3/4 of a tank and still has the issues, when the car is hot it has the issues, when you let it fully cool down and then drive it is good for the first 4-5 miles.
 
I had a 1988 744T with this exact same problem a few years ago . It was a failing main fuel pump. Have you swapped that out yet? I'd try that next.

As in the one under the car?

we have a Volvo 850R pump in the tank, the main pump is still inline and powered up. you can hear it come on.

I guess we could work at making a bypass as I have done that before, besides bypassing that we are clean out of idea's.

Well in a little I will see about trying to find a local parts store with the fittings needed to bypass it. As the 850R pump should be enough to run alone.

We did note that the amount of fuel coming out of the return line was a bit lower than we would of expected so it could be a clogged main pump.
 
Humor me, borrow Chris T's ignition computer while you're out getting parts.

113 litre per hour is the 850R pump + main pump flows at 3 bar fuel pressure at the rail, at 11.5 ish voltage.
 
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I haven't heard any mention of checking the radio suppression relay, it basically supplies power to the injectors and can fail just like the fuel pump relay. I would replace or reflow solder to eliminate that. It's located near the driver side strut tower somewhere, it's a black relay same size and shape as the FP relay.

I know that car has one.
 
Ice pack any dubious control units or sensors, if it gets better you have a suspect.
Friend had a car that only wold go about 4 miles without an ice pack for the ECU:lol:
 
The pump could be clogged, I've had a number of LH2.2-2.4 main pumps go out in this manner with they get gunked up and then will overheat , or when the internal components of the pump wear they can also run hot too.

Let us know how it goes when you bypass it.

Makes sense, lets hope that was it. Bypassed with a 1/4" to 1/2" hose barb and some 1/4" hose bypassed to the filter. Going for 30+ min test drive now.

Its a weird metric size, no? The same one the fuel rail needs.

Yup, so as said above simple bypass.

I haven't heard any mention of checking the radio suppression relay, it basically supplies power to the injectors and can fail just like the fuel pump relay. I would replace or reflow solder to eliminate that. It's located near the driver side strut tower somewhere, it's a black relay same size and shape as the FP relay.

I know that car has one.

We have tested 3-4 different RSR's and they all act the same, I have never opened one to check the joints but I will try to.

Ice pack any dubious control units or sensors, if it gets better you have a suspect.
Friend had a car that only wold go about 4 miles without an ice pack for the ECU:lol:

Really??? wild, I sure hope not, I wanted to try to fix the A/C on this after I got the running working but being that jumping 12V to the compressor it does not even power up I have a feeling the entire thing needs to be replaced.

We tried a different ECU and it idle'd higher but still had the issues SO i doubt two have the same issues, but we shall see.

Thanks again for all of the help guys.
 
Problem is still there, after the main pump bypass.

Going to go Grab a Fuel filter on maybe the off chance that that is also clogged and causing issues as the car does have 204,000 miles.
 
Ignition computer...

I meant, you already change/swap almost all that you possibly can, why not that?
 
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