1987 744Ti 177K

Car is new to me, picked it up as a parts car at the Goodwill Auction. It had a blown hose to the intercooler. After replacing that it ran much better (grin).
It still does not run right. The boost gauge indicates that it is boosting normally but it is a real dog. It has poor acceleration but once at speed seems to be able to maintain it well enough. Starts fine, idles fine, shifts fine; just your basic dog in performance. I haven't had much time to look into it but want to do that now. I plan to run a compression test and check the cat. I am inclined to think the cat may not be the problem because it seems to hold the boost gauge while trying to accelerate. I feel that if the cat was clogged it would be impossible to hold boost at normal level. Anyone have experience with a restricted cat on a turbo car. What was the behavior?

Other than checking the cat and running a compression test any suggestions on what to look into to turn this car into a decent performing brick? Thanks.

Randy

It sounds from your description like the turbo is late in spooling up? I am thinking what is happening is exhaust is escaping someplace instead of spinning the turbo. Check the turbo wastegate, because if this is letting out the exhuast prematurely, it will underboost.

Here are some other ideas & helps:

http://www.misterfixit.com/volvo740.htm

http://engphys.mcmaster.ca/~bill/volvo/database/turbos.htm

http://engphys.mcmaster.ca/~bill/volvo/database/turbos.htm


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"Can't understand why people abort Volvos, either"

Zee,

I appreciate you posting to my older thread. I have not had time to revisit this problem after I have determined that; ignition timing is correct, the engine has good compression, the turbo hoses are not leaking, the cat/exhaust system is not restricted, the AMM was swapped out for a known good one without solution to the problem. The engine does not seem to be running rich but I will check out the temperature sensor when I find out what pin to check the resistance on at the ECU.

I don't think it is a wastegate problem or late spooling. The boost gauge responds nicely and about half way into the boost area. As long as I don't try to boost the car will run at 75-80 mph without a problem. As soon as I get into pressure mode it bogs down and seems to miss/lurch. If I back off of the accelerator it smooths right out. Sure sounds like unmetered air doesn't it? The hoses have been double checked and the system pressurized with air to look for leaks that might have escaped my fine tooth comb. The boost is maintained even when it bogs down and no black smoke. My work schedule has forced me to put it aside for a while but I will get back to it. I haven't checked the O2 sensor and just because I have one I want to swap out the ECU as well. Thanks for your input.

Randy

Check your air cleaner, ours had the foam sound deadner material crumble and cause it to be clogged up.
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96 855R, 95 855,854, 90 744 Ti - 325,000 miles driven

I have been chasing a similar problem with my '87 760 Turbo and found 2 items that really did the trick...first check that knock sensor is in place (mine was physically damaged) and the connection... if bad it will retard timing all the way when driving.

According to what I read there is no real effective way to check it electrically.

They do tend to crack with age. When replacing make sure that the landing area is very clean...DO NOT tighten more than 8lbs or it will not read correctly and you could crack it.

Also make sure that the "pigtail" it connects to is not right up against the alternator..could cause interference...use zip tie to fasten it to harness away.
I was told that these often get broken off when someone lifts the eengine to do the mounts.
When you buy (if used) make sure that you get the same "style"--one with flat top and one with dome top.

Second, check the temp sensor going into the top of you radiator...if this (or the other sensors in the head) is/are bad the computer will be confused and your electric fan will not run.

I changed out these 2 items and saw a Tremendous improvement (like +20%) and smoother acceleration. Really made a big difference.

By the way, I ended up with a "spare" knock sensor when I bought 2 off eBay let me know what stlye you need...I will sell it for $15 plus whatever freight you prefer...a lot cheaper than new but it is of course "as is"

You do have a car with the "biodegradable" wiring harness (as mine)...there is a guy on eBay motors who pratically specializes in replacements. It is supposed to take 5-8 hrs and is easier with the intake manifold off...check FAQ.

I have not done mine yet, but I have carefully looked for the telltale crumbing insulation.

Temporary repairs have worked so far-- liquid tape then re-wrao with top grade 3m tape... in some cases like the brown ground wire running from the top of the intake down into the bundle under the intake.

I had to take the bundle wrap apart and repair 3-4 wires with insulation cracks 1" long hidden inside and then splice in a new wire to repalace the completely shot brown ground wire, again good connections- sealed with liqiud tape- then re warp individually and re-bundle and wrap the entire group also used several zip ties to keep it tight.

I see this as temporary, but after I was done I degreased the engine at a car was and had no shorts or problems--perhaps a little foolhardy but wanted the grime off.

Good luck and let me know if you need the used knock sensor.

David Lamb
dgltrader@comcast.net

Mine was like that especially going up hills or during higher accelerations. Turned out it was a vaccuum hose that had just deteriorated over time. db 745 tic 196k

Thanks. I need to check those as well.

Randy

By the way when I checked my hose I had originally missed the hole because I only did a visual. It wasnt until i touched every hose that I found the hole in the rear of the hose!

Check the rest of the hoses. Remove them, claen and inspect inside and out. I have also experienced AMM trouble which knocked performance. The turbo cars give little catalytic convertor trouble. It is easy to drop the exhaust just in front of the cat for a quick test, just three bolts. Be careful about the exhaust noise if you disconnect the cat.
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john

Thanks John, I forgot to mention that I had used my air compressor to check for additional bad hoses. I also checked the timing as that is exactly what it felt like but it was at 12 BTDC. Just finished compression test and they were all in the 130-135 range. I do have a good spare 007 AMM that I will try as well as the cat check. The wiring harness is degrading on this car and I would guess that might be a factor but more difficult to diagnose. Thanks for the suggestions.

Randy

I must add that my son's first car, a 1987 744T, had a bad Coolant Temperature Sensor when we bought it. It just didn't have the torque it should have until I changed the sensor. Then it had enough power to slip the clutch, and he slipped it plenty!
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john