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760 '87 760T no power, low rpm

whalepirot

New member
Joined
Jan 21, 2017
Location
kalifornika
'87 760T (USA) no power leaving stoplight

Reviving a pretty Brick; my 3rd and most challenging, supposedly needing only the underhood wiring harness, previously done on a N/A 245.

The car runs nicely, now, starts right up; idles smoothly. Mileage is 155k. Other background, below. AT shifts crisply.

When warmed up, there is almost no engine power below 1500 RPM, with little/no boost indicted. Boost seems normal, in other driving, as long as the RPM stays up. The turbo finger-spins easily, with no play felt; cold, of course. I haven't means (yet) to check FP or ECU for codes, despite Haynes(ugh) and FAQ resources. There's minimal oil in ducting downstream from turbo, nor discernible boost leaks from that piping and no audibles. I modified the heat input and made a rubber gasket to further seal out hot air from the air box. Unless leaving a stop, the car drives well, above 2200 RPM.

The FPR seems new with no gas in the vacuum line, but there is no idle change when I apply vacuum. Both fuel pumps operate.

A PO scraped away much of the AMM screen, but visually, the guts seem fine. The vacuum operated (wastegate?) unit on the turbo looks fairly new. The engine pulls good vacuum at idle, with minor fluctuation, which may indicate a valve clearance issue.

I read this: http://forums.turbobricks.com/showthread.php?t=330754 and the few other threads found.

I spent lots of time getting it started, replacing the power stage(?) on the L inner fenderwell, yet found no spark past the new coil wire; took new cap and rotor, despite the 'old' being brand new (PO). Got the O/D working with the home brew mod to the solenoid cap, and tweaked the cable for proper shifting. Plugs wires look new, Volvo brand.

Sorted out other electrical issues incl shoddy aftermarket radio install plus lots of hard plastic repairs/replacements, The leather is as gorgeous in red as the exterior white paint is!

Not interested in throwing parts at it. Appreciate help,whether links or experiences!
 
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LH 2.2 is Pre-OBD. Last year for B230FT and LH 2.2 was 1989. I'd check for boost leak caused by a bad intercooler hose.
 
Thank you.

Yes, this is LH 2.2.

Visually, the hoses are very good and listening and hand checking for escaping boost air while briefly revving it into boost, yields no 'feel' of any air.

I cleaned connectors (again) with DeOxit, all plugs/sockets but the large ones I'd done when the new engine harness. Fine tuning the kickdown helped some, and if I can get this power thing solved, will replace it, as the intake end end is frayed, but stays pretty well put.

Idle is 750. That Haynes manual is like all others; minimally helpful beyond the wiring diagram.
 
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Sorry, I should know to fill in the profile.

USA / Kaliforn

I doubt this is a fuel issue, given that it runs great unless warmed up and leaving a stop. If the dash gauge is any indication, I never see more than about half boost indication, so despite cold freewheeling of the turbo, heat may restrict its rotation, or might the waste gate be misadjusted?

I just heard, only with accel pedal floored, i.e., full boost, a rattly sound. Is the only way to test the intercooler to remove it for a visual? I have compressed air but would have to fab a plug and an input.
 
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Unless someone has swapped in a newer system (not that easy) your car is LH Jetronic 2.2. You may want to do some research on diagnosing the AMM (air mass meter). What is the tach doing when the car is acting up?
 
He replaced power stage, so I doubt that.

Visual won't be much help with hoses and IC, unless something really huge broke. Plugs and compressed air are your best bet.
 
I spent hundreds with a pal's shop, who claiimed a smoke test showed a few very minor leaks; fixed. Also had them install the kickdown cable, as he's been my at-cost parts guy on BMWs and some others, for decades.

There is no real improvement in the drive. The acceleration 'dead zone' is from idle, steady at about 800, to around 1500, when the boost gauge starts to indicate and the engine suddenly perks up; the car responding as I think it should.

Idle became erratic, then died, when I unplugged the AMM, which is no surprise, but I found no test for its proper function and I have no spare.

Not quite ready to throw an ECU at it.

I do hear a near squeal when driving with the engine revved and throttle floored. That noise stops when I lift slightly, so I wonder if it's just the waste gate. Maximum boost indicated is about half into the yellow.

The vacuum pump runs more than I'd expect.
 
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After watching a few vids, I checked the AMM. At idle the ECU 'feed' reads 2.33vdc, with a smooth increase in voltage as the throttle is opened. Battery voltage checked on another wire; grounding loss is are about 20 ohms to the (-) terminal. While spec voltages are unknown, the above seems reasonable proof that the AMM works okay.

I drove the car w/o the air box lid, after cleaning the AMM guts again (despite not looking dirty at all) with carb cleaner. I wondered if the hot air block I did, or anything else, improved the situation. It hasn't. The acceleration and idle was a bit unsteady, which I think was due to the lack of air filter, etc. as the ECU reworked the fuel tables due to more airflow.

Any suggestions?
 
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I've just gotten done solving various issues on my 87 745 with the exact same engine. When I first bought the car I would describe it in similar terms to what your seeing. I came to find out that the AMM on the car was from an LH 2.4 car rather than the correct LH 2.2. If memory serves me correctly you want to make sure your AMM has a part number ending in 007. There should also be an adjustment screw on the connector side of the housing (don't fiddle with this if you haven't read up on doing so). This corrected some of the issues, but others remained. During the replacement of the engine harness (mine was all deteriorated) I found that the PO had accidently swapped the TPS and IAC connectors. They are the same three pin style connector, however, the TPS uses two wires and the IAC uses all three. If these have been swapped, the idle circuit in the ECM is most definitely blown (mine was) and you'll need to replace the ECM (I did this as well). While you're at this point, an improperly calibrated TPS will cause a host of issues with LH 2.2, so I would recommend setting the plate and calibrating the TPS while you're in there. The last issue I had was fuel pressure related, but this was created a lean running condition. I would recommend going to Autozone and renting a fuel pressure test kit if you come to this point.

I hope this helps! You've got a couple things to check at the very least.

-Joe
 
Appreciate that, lots. I know time is valuable.

I ordered a Bosch AAM and a tropical fan clutch.

The AAM had 2 12vdc feeds on the pins and varied the voltage as airflow increased from idle; seemingly good. I wondered if the low airflow thru the intercooler might aggravate the problem. I'd seen the extreme sluggishness right after startup, on a hot day, unlike the prior post-warmup pattern.

Yesterday, I saw the second coolant depletion event, with attendant HOT ECT gauge. The puddle was mid to rear engine coompartment and it took 3 qts. to fill! I suspected a weak fan clutch and indeed, I could easily stop the plastic fan with my hand, even spin it in reverse while the engine idled. There was no loud whoosh upon start, hence the tropical Aisin.

After three recommendations to replace the (007) AMM, despite what seemed a good test, I read that an initially-failing sensor can have problems with low airflows causing the stumble I know too well. I'll also repair the wires to the aux fan with are not part of the underhood harness, but also have failing insulation.

Again, thanks for sharing UR experience(s).
 
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The replacement Bosch 007 AMM changed the driving response a little, but it's still darn near dead off a start from stop, when warmed up. The initial start, then die issue did not recur.

I am wondering if the temperature sender for the ECM is bad. It is nicely buried under the intake manifold! Repaired the aux fan wires and it operates.

I have to see if Haynes has how to the set the plate and calibrate the TPS.
 
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What do the plugs tell you? I've seen drivers in the ECU go bad in earlier 740 models too.

This is golden. Plug reading is key.
Im surprised no one has asked this yet, but is it the garrett .48/.42 turbocharger? 1500rpm actually sounds like a realistic threshold to be crossing into boost. Can the car be launched by building boost static, then attacking when the light turns green?

Just asking, becasue I just got another brick and its an 87 760 also. Garrett turbo, similar boost threshold.

Or could be way rich off idle. :lol: who knows w a thirty year old ride...:)
 
One could measure injector pulse width with a scope and watch what happens during the event.

I am bugging my boss to get the Pico back up and working but it hasn't happened. I would like to be able to do pinpoint misfire diag.

Frustrated parts darts tossing was what I was told to do on a 99 caddy that was failing smog for HC.


"It must be misfiring!!!' Let's put plug wires on it!!!" I did the plug wires as I was directed to and it Still failed!!!!

Me: Boss I want to do diag.

He: we dont have time!! Tech B says it's rusty coil terminals. Change the coils now!!!

Me: I wire brushed that ONE slightly rusty terminal. I suggest doing a cat efficiency test and a smoke test.

HE. We dont have the have time!!! Do the coils!!!

Me: ok....sure. but I did a smoke test anyways and found a small airleak.

He: I need this car gone! Do the coils

I did the coils and it still failed. Told ya so...! And now the customer is pissed.

Parts darts wastes everybody's time and money and stresses people out when it doesn't work.
 
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What do the plugs tell you? I've seen drivers in the ECU go bad in earlier 740 models too.
Drivers, meaning ECM output transistors?

The plugs looked pretty good; light brownish, tho there was a small amount of black carbonish deposit on the circular ends, not on the 'hook'. I regapped them to .032, typical for many cars, tho the Haynes, IIRC, specs .028 which seems kinda small. Maybe a turbo car needs either a smaller gap or bigger fire.

There is slightly more stumble with the larger gap and replacement Bosch AAM. While unsure how much learning the ECM does, the older AAM seemed better. After it cools, I'll regap the plugs to spec. It revs in neutral nicely, but had a slight roughness as the RPM bottomed out. Not sure it that's new, 'cause I did little neutral revving before. With a smooth 8-900 RPM, I kinda doubt the IAC is off much. That roughness lessened after a few revs, so maybe the ECM was adjusting.

It has lost coolant at times, but the last episode may be due to high ECT from the bad fan clutch; tropical replacement here in a few days. That was also w/o A/C on and failing lead wires to the aux fan. There's no milky-oil on the dipstick, just clear oil.

I wouldn't know a Garrett turbo from any other, just that I felt no end play and free spinning when it was cool. The boost gauge never reads above half-yellow. I thought the other 740T we had went higher, but I think it was a '90; maybe a diff turbo.

I'm reluctant to launch it by revving in neutral for driveline stressing/breakage reasons. I did that once a few days ago and was not impressed!

I am doubting this is low fuel pressure, as the car runs great uphill, at speed and even if accelerating; a high-demand fuel period. Again, I smell no fuel nor detect any gasoline in the FP reg VAC line. That regulator looks new (PO) but I hear little if any RPM change if I pull that VAC line off or use my HandiVac to pull vacuum on it. Perhaps that diaphram has hardened, but that seems like parts tossing! I'll redo, measuring VAC line reading/variation, and metered RPM change with my HandiVac.

Appreciate the committee!
 
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While unsure how much 'learning' the ECU does, the car is improved.

I pulled the intercooler, as the simplest way to swap in a new tropical fan clutch. After cleaning the grossly filthy plastic fan, the FCP-sourced (their site says it won't fit) is in, and as expected, noisier. I see little, if any, drop in ECT in hi 70's weather. While the I'cooler was out I checked it for leaks with my huge shop vacuum, detecting none. A de-greasing, rinse, dry-out, with no leaks detected with liquid, either, back in it went.

After not a LOT of driving, it is better off stop, which may be due to improved I'cooler function (more airflow), akin to closing off the hot air feed in the airbox. This step up feels larger than post AAM change, using my SOTP* gauge.

The max boost indication is just below half-max deflection, so I'll adjust the boost a bit. I recall our last 740T as peppier, with higher indication.


* Seat Of The Pants
 
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Appreciate that, lots. I know time is valuable.

I ordered a Bosch AAM and a tropical fan clutch.

The AAM had 2 12vdc feeds on the pins and varied the voltage as airflow increased from idle; seemingly good. I wondered if the low airflow thru the intercooler might aggravate the problem. I'd seen the extreme sluggishness right after startup, on a hot day, unlike the prior post-warmup pattern.

Yesterday, I saw the second coolant depletion event, with attendant HOT ECT gauge. The puddle was below the firewall, and it took 3 qts. to fill! I suspected a weak fan clutch and indeed, I could easily stop the plastic fan with my hand, even spin it in reverse while the engine idled. There was no loud whoosh upon start, either, so I have a tropical Aisin coming.

After three recommendations to replace the (007) AMM, despite what seemed a good test, I read that an initially-failing sensor can have problems with low airflows causing the stumble I know too well. I'll also repair the wires to the aux fan with are not part of the underhood harness, but also have failing insulation.

Again, thanks for sharing UR experience(s).

The coolant leak was most likely the heater control valve. The ECT is temperature sensor for LH2.2, not for the gauge.
 
Drivers, meaning ECM output transistors?

The plugs looked pretty good; light brownish, tho there was a small amount of black carbonish deposit on the circular ends, not on the 'hook'. I regapped them to .032, typical for many cars, tho the Haynes, IIRC, specs .028 which seems kinda small. Maybe a turbo car needs either a smaller gap or bigger fire.

There is slightly more stumble with the larger gap and replacement Bosch AAM. While unsure how much learning the ECM does, the older AAM seemed better. After it cools, I'll regap the plugs to spec. It revs in neutral nicely, but had a slight roughness as the RPM bottomed out. Not sure it that's new, 'cause I did little neutral revving before. With a smooth 8-900 RPM, I kinda doubt the IAC is off much. That roughness lessened after a few revs, so maybe the ECM was adjusting.

It has lost coolant at times, but the last episode may be due to high ECT from the bad fan clutch; tropical replacement here in a few days. That was also w/o A/C on and failing lead wires to the aux fan. There's no milky-oil on the dipstick, just clear oil.

I wouldn't know a Garrett turbo from any other, just that I felt no end play and free spinning when it was cool. The boost gauge never reads above half-yellow. I thought the other 740T we had went higher, but I think it was a '90; maybe a diff turbo.

I'm reluctant to launch it by revving in neutral for driveline stressing/breakage reasons. I did that once a few days ago and was not impressed!

I am doubting this is low fuel pressure, as the car runs great uphill, at speed and even if accelerating; a high-demand fuel period. Again, I smell no fuel nor detect any gasoline in the FP reg VAC line. That regulator looks new (PO) but I hear little if any RPM change if I pull that VAC line off or use my HandiVac to pull vacuum on it. Perhaps that diaphram has hardened, but that seems like parts tossing! I'll redo, measuring VAC line reading/variation, and metered RPM change with my HandiVac.

Appreciate the committee!

LH 2.2 is not self learning. The plugs for turbo engine do use a smaller gap. NGK plugs are good. You didn't mention the plug wire brand. Okay, yes you did mention Volvo wires. Do they have a class letter and date?
 
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