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760 '87 760T no power, low rpm

Add to that, the low vacuum, which is why I checked the cat. I cleaned out all its internals but won't install the new one util the car runs. Hopefully, none of the pieces moved back to the muffler.
 
I have a non-turbo 740 which had similar problems. Turns out mine was all corrosion related - I started measuring block to battery resistance through ground, and had well into the 15 ohm areas. intake manifold to battery was closer to 400 ohms. I took a bit of 10 gauge wire, and just went and tied everything together, block, alternator, battery, frame, manifold, headlight grounds, etc.

Next start, I have GREAT lighting again, but the engine runs SUPER cruddy. So I disconnected the battery, and turn everything on that I could find - so as to discharge any remaining capacitance. Reconnect battery, fire her up, and it's running OK, but not great. Took it down the road, by the time 5 miles was past, the rig runs great again!

Read this thread, and while it looks like you've been dealing with corroded insulation, don't for get to take a look at the grounding straps and the reading from them to ground on bat.

Just a thought. works for me!
 
Thanks for that. I'd checked grounds, having had plenty of ground loop problems in another car and knowing the sensitivity of all newish cars to proper signal paths, including grounds, which are oft overlooked. Such is frequently solves the noise issue in car audio systems.

Unlike many, we live in a warm dry climate and rarely see rust or corrosion of nay type. I could not recall the resistance readings I'd taken in this car trek, so I redid that and found a maximum of 1 ohm, which was at the metal panel that holds the ECU.

Having just gotten back the electronics from a shop, I started the engine after reinstalling them all. It ran for about 3 seconds. I tried again and saw there was no tach indication either, which I think points to the Hall sensor. Going to research that now.
 
If the hall sensor is bad the engine won't start, was the engine running without the tach doing anything? That sounds like a wiring problem to me. The tach is driven directly off the ignition coil IIRC, if it's getting a spark then the tach should do something. I suppose a bad tach could cause lack of spark but I've never personally seen that.
 
The engine is idling, to see if it will quit. I found 6.4 vdc at both coil primaries, so pulled the FI relay (looks new), then checked the noise relay in/out at 12vdc. Hmm. Decided to check the coil again and found proper (12v) at both primaries. When I pulled the FP relay after it idled for a few minutes, it felt warm, telling me something may have high resistance, so I contact cleaned the socket, then let it run for a stretch.

Boost below 1300 rpm is non-existent, still.

If the hall sensor is bad the engine won't start, was the engine running without the tach doing anything? That sounds like a wiring problem to me. The tach is driven directly off the ignition coil IIRC, if it's getting a spark then the tach should do something. I suppose a bad tach could cause lack of spark but I've never personally seen that.
I was so surprised the engine started, I failed to see if there was a tach indication! It had been working just fine.

Prior, there was no spark and I'm about to check again. I smell fuel so am quite certain the pumps are working. There is no spark... again!!

Time to peruse the troubleshooting flowchart.. AGAIN.

Someone disconnected the vacuum line for the overboost switch, for whatever reason. I tested it okay and am reconnecting it via a T to the boost gauge and CC pedal switch. (The cruise wasn't working either).
 
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On my 88 765 Turbo the tach was erratic when the aftermarket powerstage was failing. Installed a good used Bosch powerstage and cured the issue.
 
Yeah, old thread. Old guy, too with real old problem! I needed a long break from slow-Volvo-World. Car has a history of worsening boost levels.

Engine runs great, sort of; starts right up after sitting for months, then idles like a purr-fect engine. Tis a replacement Swedish red block of relatively new stature.

Today, I installed the brand new, CARB certifed cat (old was cheap aftermarket w/melted core). With no boost and vacuum gauge readings indicating 'maybe', I'd checked for exhaust blockage. A (easily missed) sticker on the box says to do a run-in procedure to set its guts properly: 5-10 minutes at idle, then 2 minutes at 2500 RPM, then drive the car.

So I did. The boost is non-existant, until 3rd gear, under hard acceleration, where it was maybe 2-4 pounds. Car is a real bow-wow from a stop. I'd checked the vacuum-actuated device (looks shiny and new) on front of the turbo and for leakage in its vac hose from the intake. Audible clicks heard when adding/stopping vacuum to the actuator and vacuum held solid at 22# when I connected the IM end to my hand pump instead of the intake.

I'd checked for end play and free spinning of the turbo 'back'when'. Both okay and no blue smoke from tailpipe.

I was surprised to see any boost indication, as w/o the cat the dash never indicated anything but vacuum. Previously, I'd adjusted the waste gate lever with no real improvement in this long-existing problem. Maybe it's time again, after the new cat?

Son's graduating and we want this car for him.
 
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i still think there is something fundamentally wrong in the wastegate + control setup: wastegate not properly closed when it is supposed to be = no or very late spool-up
Your story reads like there is no closed wastegate inside the turbinehousing...wastegate port open all the time...
 
i still think there is something fundamentally wrong in the wastegate + control setup: wastegate not properly closed when it is supposed to be = no or very late spool-up
Your story reads like there is no closed wastegate inside the turbinehousing...wastegate port open all the time...
Thanks for that, truly!

I don't know how to check that, so will look for that procedure.
 
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you could investigate the wastegate by undoing the downpipe and use a small mirror and a torch to take a look inside the turbine housing. Look for a closed wastegate port.
manually open the wastegate by pulling on the actuator rod. and see if the gate opens up.
Also see if you can find evidence of cracks in the wastegate port and/or wastegate valve.
 
zeroing in?

I got in there today, fun as it is. Thanks so much. There is such a dearth of info on this car, even via AllData at my pal's shop.

I was unable to see much of anything with light and a mirror, but I have a (invaluable) Snap-On boroscope. Bending the lighted tip and moving it around, I was able to see the flap that closes off the exhausted gases, thereby using all that energy to spin the turbine; controlled by the shiny newish vacuum pot at turbo's front. There was no way the control rod length was allowing it to close and after detaching it, I found some binding in the flap's movement. Exercising it back and forth a few times seems to have freed it so it moves easily, full swing. that cpontrol rod is way off in adjustment, probably wrong since the vacuum pot was changed by a PO. Sadly, I did not see enough detail for cracking.

Tomorrow, with more light and energy, I'll address that rod length issue, then reassemble the down pipe and shroud. I expect and feel this old Swede brick may hop away from stops quite spritely. The minimalist Haynes manual at least has the adjustment procedure.

I'm still quite sure there is a incorrect vacuum hose setup, akin to what I found, done by a PO, with the wiring. I have a number of vacuum hose diagrams, for various cars, but this '87 turbo has no underhood sticker. At least at this point, that may just mean the CC won't work and the vacuum pump runs too often; neither a safety issue.
 
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progress! let us know how that correctly adjusted wastegate does.
I predict a nice improvement.
 
True progress and thank you for your help. This 765 has near perfect leather and paint; shows very well. Despite the improvement, which I'll TAKE, I feel I'm back to the performance issue of months ago.

Haynes says proper wastegagte adjustment is accomplished with 7psi applied then adjusting the lever length. Compressed air does activate the mechanism, but I've no easy method to apply exactly 7psi. I readjusted it to be fully closed, with urtrher slight closing pressure at zero pressure. Perhaps it needs another turn?

Drive: The car is very slow from a stop, until around 2000 RPM. Unlike earlier, it shows some boost, then more as the car anemically accelerates. More boost is indicated at higher revs/velocity, but never more than 1/3 gauge deflection. There is some engine stumbling with added boost, accompanied by poor acceleration. At best it drives reasonably well as long as the revs stay above 2000 RPM, though I don't think it's truly up to par. I was also told that this aged engine control has no learn capability. True?

A professional mechanic (not a Volvo guy) mentioned that some cars employ a computer controlled solenoid to limit boost until the engine can handle it. I recall reading about them, but don't know if this car has one. I'll check the wiring diagram, assuming it's corrrect. I mentioned that the removed cat's internals had melted, probably from whatever condition existed, perhaps running too rich.

I've not made an apparatus to verify proper fuel pressure.

I did get some vacuum hose diagrams and am seeking where to post them for others' use.

I feel close to a solution; then again, Ive felt that before!
 
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Not much change in idle when pulling the vac hose from the newish FPR, but... one thing at a time!:-P

Cranked 1 1/2 turns more pressure on the WG rod; still a dog from stop, but better elsewhere. I think the still-existing stumble may be erroneous A/F ratio, due to mismatch between boost and fuel injected, least for now.

I tried another 1/2 turn in the adjustment, but it worsened. I'll back off a notch, then try to find a way to check the fuel pressure, having a gauge but no port. I saw how to make a tool, but haven't yet.
 
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For things as they are, that 1/2 turn out is the sweet spot; still a bow-wow and when accelerating, i have to 'feather' the throttle to find where the car will accel best; not stumbling some, despite the boost seemingly normal. I hear a whistling (suppose it's dumping boost) at halfish boost needle, under load in say, 3rd gear with RPM 3k+/-.

With fresh gas, I rechecked idle vacuum and FPR. Still very little, if any change when pulling the vacuum from it. The MAC shows 15psi vacuum, rather low, and slow variance of about 1/2 psi. along with a slight variance in idle speed. Interestingly, I recall 22 psi earlier from a different port on the intake.

"Vacuum readings at idle much lower than normal can indicate leakage through intake manifold gaskets, manifold-to-carburetor gaskets, vacuum brakes or the vacuum modulator. Low readings could also be very late valve timing or worn piston rings.

James10952001 said maybe the cam belt is off a notch; I've still not checked, but with the vacuum diagram finally in hand and known leakage in parts (iwth frequent pump runs), that's where I am headed first.
 
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maybeeee fixed???

Spoke with a mechanic who'd worked on this car, who said either the ECU or timing. I'd had the ECU and both AMMs checked by an ex-Intel guy in Phoenix. Certain Porsches use the same injection system; 928 is one.

Instead of fabricating a FP port to check the fuel side, I pulled the front accessories and found the belt off about two notches. A bit of a wrestling match to move the tensioner (it spins easily, smoothly and w/o play), I tightend the nut and the engine foired right up. It runs smoother and seems w/o variance in vacuum, now at 19", or RPM. The throttle snaps the revs up, unlike the bad lag before. I ran out of time and light to rempount the cover, belts and fan, but am eager to (hopefully) get this old brick hopping like it should. :cool:

More to come, hopefully the final frontier!
 
good progress. I think you have found the true cause. 2 teeth off (most likely retarded) is a lot. that will make the engine run like a limping dog.

about that tensioner, in case you want to do a belt swap in the future: there is a guide pin going through the spring. It has a hole in it. You can squeeze the spring with some pliers and insert a pin through that hole.
That way you have pre-tensioned the tensioner and you can easily install the belt. When you are confident that you got it right you just pull the pin and -pop- the tensioner takes up the slack in the belt.
After that, make one manual crank rotation of the engine, then tighten the tensioner nut. Fixed!
 
I think you have found the true cause. 2 teeth off (most likely retarded) is a lot. that will make the engine run like a limping dog.................there is a guide pin going through the spring
Thanks, and a special thanks to you, as assisting in the solution. You should know that this fix will relieve me of a nagging to-do (of which I have a plethora) and bring smiles to my son and wife!

My Haynes manual mentioned the hole but not that it is in the slider plate at the right end of the tensioner spring. I had some difficulty finding the 'right' tool to compress the spring to see, then insert a pin to hold it. I used a long, slim pry bar as no clamps fit.

Perhaps many of the other suspect components needed replacement or checking anyway, but all that effort/cost delivers more confidence in the car and aligns the mechanical condition with the near-perfect body and interior.
 
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