87 740 turbo wagon dies
 

A friend of mine just bought a 740 turbo wagon and we were working on a few things today. It has over 200k on it, but it appears to be in really good condition, despite the mileage. I followed him back from picking up the car over in the next county last night. It ran fine back here with no issues, but it hiccuped once, and quit. He ran over a big bump, it quit but restarted.

Today, it ran great, but it was stuttering when you would try to briskly accelerate. Easing into it, when you hit around 3500, it would stutter and hesitate. But, letting off the gas it, idled fine. The last time it did this it it simply died.

We figured it was fuel or spark, and soon smelled gas out the exhaust pipe. So it appears the spark has left the building. It has new tune up parts on it... cap wires and even the coil looks new. It just spins w/o any attempt to catch and run. [I looked down the oil filler cap and seen the cam still turns .. no broken timing belt..:p].

Also it looks like the coolant temp switch was replaced recently. He only paid 500 bucks for the car and it sure would be a shame not fix it, as the rest of the car is solid. Where would be some good starting points?

The wiring harness has a good bit of tape wrapped around on it.. I guess this was one of the "bio-degradable wire insulation" years.. lol :eek:. I'm going to go with him to the junkyard and help rip out a good harness from that 760 2.3 I got other parts from.

Any ideas? When it ran it really ran strong...

Thanks in advance,

Mike

sounds like a wiring problem to me, too. for the engine to get spark, the hall sensor in the distributor has to make it to the ICU (Ignition Control Unit) which is behind the glovebox, then the signal from the ICU has to make it to the ignition power module, and from there to the coil, then you get spark.

make sure the donor car has the same version fuel injection... around 89 or 90, the turbos switched to LH2.4, your 87 is LH 2.2.

later cars have the distributor on the back end of the camshaft, and use a crank position sensor on the back of the engine block that reads from a tonering on the flywheel instead of a hall sensor in the distributor. frankly, I'm not sure which system was used on a 87 740T (my 92 740T has the newer system). that crank position sensors wiring is particularlly subject to problems due to its position where it gets baked.. as its under the distributor, its quite hard to access.

Hi Pierce,

Thanks for the lightening quick reply! After searching a bit more we just went out and yanked two plugs. Number 2 and 3 plugs were dry... I also hooked a timing light to number one and the light did pulse while cranking... BTW this year is weird, I guess, BC it has the dizzy on the back of the head, just like my 92 940. So this has no pickup inside, I guess. So it must be LH2.4?

It appears it may be a fuel issue after all... as now there is no fuel pump priming noise when the key is turned on.. I listened at the tank and felt the undercar pump as well. The undercar pump looks very new, but the filter is cruddy as, ... Shouldn't the undercar pump make noise as the key is turned as well? Does this explain the lack of power at 3500 rpm?

Also, I had a spare white fuel pump relay and swapped it over to no effect, and also we went over the fuses in the block... all were good.

Any suggestions are appreciated.

Cheers,
Mike

LH2.4 cars have a diagnostic block on the foreward side of the left strut tower under the hood, near the power steering reservoir. this is a black rectangular block with a cover on top, under the cover is 8 numbered holes, a button and a LED, and a jumper wire on the side. does this car have that?

Hi Pierce,

Just went out to have a look... No, this car only has a relay in that location, right next to the power steering reservoir. However, I did see a black plastic square raised female plug, facing straight up, near the end of the fuel rail up on top. Of the 4 cavities in this plug, 3 have metal female terminals inside. I don't know if this is a diagnostic port or not.

We looked at my sons 91 740 and his was set up exactly as you described. Is this a hybrid system or some weird transition year thing? :confused:

Thanks for your help!

Mike

+1 on the wiring, HALL EFFECT sensor and wire going into the harness.

Your car has a HALL, as all '87's do, in the DISTRIBUTOR as all 740's.
Your car has NO diagnostics box, they come later.

I'd address that HALL first...

Hi lev,
Thanks for the tip. I'll be digging into this again after work. This motor has the dizzy on the back end of the head, not the block as I have noticed elsewhere. Do I have to remove the dizzy to replace the sensor? Also, does this sensor trigger the fuel pumps to cycle as well? I Plan on direct wire testing the pumps too. I did get the timing light to flash, indicating spark, but the spark was kinda yellow when I stuck a screwdriver in and held it near a ground. I'll post my findings, thanks again!

Cheers, mike

the fuel pumps should come on for about 1 second when you turn the ignition on, then stop til the ECU senses crank motion via the hall sensor (or CPS sensor on LH2.4 cars) where it comes back on and stays on til the engine stops. the 'fuel pump relay' actually has two relays in it, one side provides power to the ECU and the rest of the injection system, this comes on with the key and stays on, the other side provides power for the fuel pumps only, this does what I said above.

[btw, sorry about the confusion with the cam-end distributor and lh2.2 vs 2.4, I forgot that the 740's used the cam end distributor with BOTH systems, my 740 is a 92 with the LH2.4]

Hi,

We just went out and applied 12 volts to the three wire plug that leads to the in tank pump. 12 volts + was applied to the red wire.. there were also grey and brown wires. I touched ground briefly to each of those and there was no activity.

We tried to cold start it.. and still nothing there. I pulled the coil wire and seen it was sparking to ground ok.

Should I check the undercar pump in the same manner? What are the odds that both pumps simultaneously failed? The undercar pump looks alomst new.. It's weird .... you can smell gas when cranking.. but it just wont run... Im totally baffled..

Thanks for the replies!
Mike

Ok... just pulled the return line from the fuel pressure regulator and cranked the engine over... we got only like 1/4 inch of gas in a snapple tea bottle, after 15-20 seconds of cranking.. ... So the pump tank is toast? Also the gas that came out was smelling pretty bad.. the stale varnish smell... I'd guess it ought to be flushed out when the pump gets changed.. The undercar pump seems to click when the key was turned.. just once every time the key is turned.. Thoughts?

Thanks, Mike

I think I'd get the car up on a lift, and disconnect the line that goes into the main pump, and put THAT into a snapple bottle and repeat your test (or, instead of cranking, you can jumper the pump power at the fuel pump relay socket), and see if you're getting adequate fuel flow from the tank pump. if you are, then its probably the main pump and or fuel filter. if not, then its more likely the tank pump.

and yeah, nasty old gas isn't going to do anyone any favors, I'd siphon most of that out of the tank and put in 4-5 gallons of fresh clean gas.

Hi Pierce,

Update... We met up here and spent some time working on the car. My friend went and bought a new in-tank pump and sock. In his exuberance, he removed the tank pickup assembly and ripped apart the pump without first taking pictures of how the assembly went together or where the flat clips went.. [I was in the house finishing dinner, so I never seen how it was originally]. So, now I'm online searching for a few pictures of the assembly.. I guess maybe the factory manual would show the best detail, as to how it fits..

If anyone here had a shot of it I would be highly grateful..

Anyway, we noticed the replacement pump is shorter than the original.. BTW it appeared to be the original equipment, so replacing it is required anyway as I see it. Next up was taking a closer look at the under car pump. The positive wire to the pump had the insulation completely gone, from the shielded portion of the loom, to the plug itself, exposing about 3" or so of bare wires... not good. I noticed the pump itself looked like it was fairly new, but the filter was a totally rusted can. I gave him money to go pick up a new one at the parts store.

The plan for tomorrow is to drop the pump and filter bracket, bench test the pump and replace the ugly filter. With those things out of the way, I'm going to clean and try to wrap up wire to the pump. If the pump tests good, it's gotta be the clogged filter maybe..

Any ideas where to look next, if the positive wire to the under car pump is not getting voltage? Hopefully the rotten filter was the culprit..

Cheers,
Mike

power to both fuel pumps comes from the fuel injection/pump relay, which is relay "E" in the main relay panel behind the dashboard. from there, it goes to the top side of fuse 11. the top side of fuse 11 also goes to the main fuel pump, via a pink wire (so the main pump is NOT on the fuse), and the bottom side of fuse 11 goes to the tank pump (so that one IS on the fuse). fuse 11 also powers the O2 sensor heater.

so, if you pull fuse 11, and stick a pin into the top side of it, and hook a volt meter from that to ground, when you turn on the ignition you should see a ~ 1 second spike of power if the relay is working. if you see power there, and don't see power at the fuel pump, well, then the wire in between is probably bad. there's a 2 pin connector 'L' in the middle, where the fuel pump hot wire is pink, and the ground wire is black, I'm not quite sure where this "L" is, but I think its behind the dash somewhere. I'd guess your problem would be with the wiring on the exterior.

Hey Pierce,

Got some more done on the car tonite. The new in tank pump was tested [hooked up and by turning the key with it not fully installed in the tank.. just to visually verify it was working..] and reinstalled. We then moved on to replace the fuel filter and get a closer look at the under car pump. We replaced the cruddy fram filter and bench tested the pump. It works...

now the weird stuff... everything was put back on the car... lines hooked up etc, but no pump sound with the key and cranking... I tried replacing the white fuel injection relay in the panel... nothing... The rotten looking positive pump wire was cleaned up and re insulated, then installed.. There is nothing powering up the pump.

Tomorrow I'm going to try the test procedure you outlined... I pulled fuse 11 and it is good... If fuse 11 is good... ??? I'm stumped... :confused:

Sorry for my ignorance, this is my first complex/newer foreign car. I'm kinda learning as I go here. Thanks for your patience and input.

Cheers,
Mike

like I think I said, I'd pull fuse 11, stick a spade lug or something into the top socket of fuse 11, and use a volt meter to see if there's +12V between that pin and a ground (the shell of the cigar lighter socket is ground) for a second when you turn the key from off to on, and steady 12v when you're cranking.

if you don't have 12V there, then I'd be looking at the fuse 1, and the fuel pump relay...

fuse 1 provides power for the whole fuel injection system, and the fuel pumps (fuse 11 is downstream from it, on the power for the tank pump only)

pry the plastic surround off the cigar lighter, and remove the screw behind it, and the tray thats above the ashtray comes out for easier access to the relays behind the fuses. there's three rows of relays, the leftmost of the middle row is the fuel injection + fuel pump relay (it has two relays inside the can). pull the relay,

Hi Pierce,

Just was out at the car and performed the tests you outlined. I found power at fuse 11 as you described, and also power on fuse 1. Both fuses are good, but still no fire. I can smell raw gas at the tail pipe too... Could it be the crank position sensor? I suppose this fires the injectors and also tells the spark when to hit? I pulled the coil wire and found a weak yellow spark. Or is it the Hall effect module, as Lev mentioned? The fuel system seems to be working and has a new filter to boot. Is there a way to easily test either component or is this pretty much a plug and pray exercise? LOL.... I really do appreciate your input!

Cheers,
Mike

if the crank sensor is dead, the pumps wouldn't have spun when you cranked. wait, this is a 1987? that has LH2.2, which uses a hall sensor in the distributor, its only LH2.4 that has the crank position sensor. but, yeah if that hall sensor was dead, there'd be no fuel pumps on crank.

ok, sounds like now we're looking at ignition... lets see... hall sensor goes to the ICU (Ignition Control Unit) which is behind the glove box... ICU sends pulses to the ignition power module, and that fires the coil, which makes the spark. I don't have wiring diagrams for a 87 740 handy so I can't be any more specific, but they may be online somewhere.

Yes, called the parts store and found out there is no crank sensor for 87. They do have a pickup assembly for the distributor for 68 bucks tho. We pulled out the dist. and really cleaned things up. Put it back in and tried again.. I can def. smell gas, and there is a weak yellow spark.. so there is gas and spark but it wont even try to run.. I just cleaned up the plugs and I'm out of ideas...

Thanks, Mike

for ignition problems, see Electrical-Ignition for lots of stuff.

an 87 could be REX or Bosch EZK ignition. Bosch has a conventional cylindrical ignition coil with a seperate power stage. Rex has the power stage and coil integrated, and looks more like a rectangular transformer thing. above FAQ covers both.

Hey Pierce,

Thanks for the tip.. I guess it's Bosch with the conventional looking coil. I'll check out the link and hopefully figure this thing out.. Its def. getting gas now... But that weak yellow spark mustn't be enough. I'll post my finding between rains here.. :o

Thanks again!
Mike