Horsepower problem (86 740 Turbo)

jgrant1980 · Post by **jgrant1980** » 27 Jun 2003, 09:27

I just purchased a 1986 Volvo 740 Turbo Intercooler. She's HOT!
http://www.jasonmgrant.com/volvo
Now, the bearings in the turbo were shot so I replaced the cartridge
($$$).
There is a new problem, however.
Here are the common problems with the car (maybe you can use this
miscellaneous information to diagnose my horsepower intermittency
problem):
1. Fuel gauge does not work (worked for 5 minutes yesterday ONLY;
when I bought the car, they told me it had not been working for
sometime)
2. Temp gauge is intermittent (turn car off and restart usually fixes
this)
3. Just changing the plugs (did not fix intermittent horsepower
problem)
4. Just had turbo completely rebuilt (very expensive)
5. When started in cold, she'll 'hunt' between 1000 and 1500 until warm
6. Will die sometimes at a red light
7. Looked at old plugs - it is burning properly (as told by Volvo)
8. Oil pressure is fine.

Here is the problem. When I jam the pedal down, it will sometimes
boost and sometimes it will lag. When I go on the highway, and decide to
pass, sometimes it will run like a bat out of hell, while other times
it will sputter and lack horsepower. Other times, the horsepower loss
will only last a few seconds and then the car will fly!

Thanks for any info.

Volvord · Post by **Volvord** » 27 Jun 2003, 12:10

This could be caused by several things. I had an 87 760 Turbo with similar symptoms, the cause was a faulty ground on the fuel tank sending unit. This gound not only grounds the fuel sending unit but also grounds the fuel pump in the gas tank. If this primary fuel pump is not working, or working intermitently, it will cause many of the drivability problems you have describes. Access to the fuel tank sending unit is through an access panel bolted to the floor of the trunk

Good luck

jgrant1980 · Post by **jgrant1980** » 30 Jun 2003, 06:37

Are the pump and the filter integrated? Where is the pump located and where is the filter located? I was also told by someone that it could be the fuel relay overheating. Perhaps that needs to be replaced also. Is there even a fuel relay in my 1986 Volvo 740 Turbo?

Is there more than one pump? What about filters?

- J

Volvord · Post by **Volvord** » 30 Jun 2003, 09:13

All Volvo 700 series use 2 fuel pumps, a pre-pump in the fuel tank that supplies a large flow of fuel at about 15 psi to the main pressure pump located under the center of the car by the main fuel filter. This main pump pressurizes the fuel for delivery to the injectors. If the pre-pump fails the main pressure pump will not supply a steady or constant supply to the injectors, hesitation, bogs, flat spots and even stalling are common symptoms.

It may be the fuel pump relay, these also have been known to fail. There are several good repair manuals at your local parts stores on your car, I would pick one up and follow the diagnostic process for each component. You could also look at http://www.brickboard.com/FAQ/700-900/ this site has many diagnostic procedures that may help.

jgrant1980 · Post by **jgrant1980** » 02 Jul 2003, 09:26

Dammit. I found a vacuum leak in one of the hoses.

It was under the metal ring on a hose.

I was just about to take the car out after semi-patching the hole (just as test), when the car started billowing white smoke (not from the exhaust) from under the hood. She pissed fluid everywhere.

It seems to be leaking from directly under the engine block.

Since I just had the turbo cartridge replaced, do you think it could be a lose hose that the mechanic improperly attached?

There doesn't seem to be antifreeze in the oil (check the dipstick) and the car is not pushing out white smoke from the exhaust.

When I turn the car over (for a brief 1 or 2 seconds), all the pistons seem to be firing.

Is it the water pump or the head gasket?

Should I be bracing for a huge repair ahead of me?

Thanks again.

jgrant1980 · Post by **jgrant1980** » 09 Jul 2003, 08:53

Hi again,

I found out it was the block heater that had a leak. Replaced that and refilled the coolant - no leaks.

During this time, I found a small hole in one of the boost hoses. I patched it temporarily and noticed a superior performance increase.

I am thinking about dumping the air intake box and replacing it with a K&N air charger (cone type). Now, I hear that this is a poor decision due to the temp of intake air. Especially in a 740 turbo.

Please advise.

Thanks

Volvord · Post by **Volvord** » 09 Jul 2003, 09:59

Do not remove the air box, the air filter and box on the 700 turbo is larger than any V8 and capable of delivering air to a highly modified engine. The only modification that is usually done is removing the air restriction horn in the air box. To do this remove the airbox and on the cold inlet side you will see a venturie like plastic tube inserted into the larger intake, simply remove the screw and pull out this venturie. There will be a slight increase in intake noise but airflow will also increase.