I am in the position to purchase a "pristine" 1990 740. It could go on any show room in the world. It is that clean.

Starts up and idles great but and I mean but will not go over 25 mph. It just wants to die. Had a good mass air flow sensor put in but that is not the problem.

I need ideas (I guess help) to determine what to look at. It did pass smog in CA just a few months ago. It has been completely serviced and maintained on a regular schedule, and that is why it is very attractive. I suspect a simple sensor malfunction......But which one????

Thank you for any help!!

Replaced the fuel filter and pump, as well as the mass air sensor. No change. Could it be the O2 sensor???

You should consider taking the car back to the dealer that tuned it up.

Swapping parts can add up to $$$ real quick.

You might represent a new customer to them, and therefore they might treat you right.
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96 855R, 95 855,854, 90 744 Ti - 343,000 Volvo miles put on 7 bricks

James, I am not going to throw new parts at it. As far as the dealer, that was 7000 miles ago.
I have been looking at fuel pumps online. They state a master which is on the frame and a transfer pump in the tank??? What does it transfer??? Let's see....you bought Arco last week and Shell this week. I think I will let you run when you buy Sunoco... What exactly is this??

The car has not sat around but used by a Doctor to go to work. It has been from CA to NY three times without a problem. The car has 123,000 miles on it. Volvo recently did a complete service on it including full tune up, timing belt, valve adjustment, brakes etc. It cost him almost $2000 to as he said "completely go through the car". He was going to give it to his grandson for college but things changed.

To make a long story shorter, I bought the car today for $500. I know it was a steal but that was his price because he wanted it gone because of what happened. (Something about an old farts car comment) He was driving it last week, came home to pick up something, backed out of the driveway and it would only do about 25 mph????

So, Is the fuel pump in the tank?? Do I check fuel pressure on the rail?? I looked in four different stores today and found manuals up to 1988 and from 1993 but nothing for this car.

Thanks

there are 2 fuel pumps, a low pressure 'transfer' or 'pick-up' pump that get the fuel out of the tank and to the main or hi-pressure pump that is in a bracket directly under the drivers seat (outside) with the fuel filter. there is also a strainer type filter on the inlet to the pick-up pump. the high pressure pump is a centrifuge type and can't prime itself so the pick up pump gets it to the other.

check the pressure at the rail.

I'm sure it is something simple with fuel system, otherwise idle would be a problem. As posted, fuel pump is first suspect since pressure regulator would affect idle. If it has been regularly serviced the fuel filter has probably been replaced, but might want to check it and the in tank filter.

This may be far reaching, but how long has the car been sitting? Is it a low milage car that sat with same gas in it for a long time? May need to flush tank and put in good gas.

If its in that great of shape and is a great buy, I'd personnally buy it at the right price and figure it out. You have a great bargaining tool to get it for a good price. Price it were you think you may have worse case of replacing injectors, fuel pumps, filters and pressure regulator.

I picked up an 86 740 in great shape 5 years ago for $2000.00 with idle problems and bad ring gear. The idle problem was just a clogged flame trap and needed good TB cleaning. It has given me great service (but I do continual preventative maintainence) and not afraid to drive anywhere.

Gary

Try the fuel filter and or fuel pump in tank. Is it worse with more throtle, or does it remain the same regardless of throtle imput?
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65 122, 73 P1800ES, 79 242GT, 80 262C, 81 242, 87 780,88 745T X2, and a plethora of parts cars and eventually to be finished projects

I'd check the fuel filter and the main pump.

either the filter is mostly clogged and allows enough fuel to idle but when you open the throttle the fuel pressure would drop.
or the main fuel pump is out, with the in-tank pump providing fuel at a lower pressure.

if the car has been sitting I'd suspect the filter. the gas could have gone bad or been contaminated, and even if they changed the filter, if they didn't do anything about the bad fuel the new filter would likely clo0g up in short order.

Don't think these cars can run with the main fuel pump dead. Maybe a partially clogged cat?