1988 Volvo 740 Turbo stalls 10s after start

mrt740 · Post by **mrt740** » 27 Jan 2024, 13:57

I recently bought a non-running 1988 Volvo 740 Turbo (B230FTLH 2.2 AW71). The fuel pump and filter, injectors, fuel injection relay, and spark plugs were recently replaced by the previous owner. Car would run on starting fluid. Tested the fuel pumps by disconnecting the line and pumping gas into a bottle. They pumped plenty of gas. While testing the injectors noticed one connection to the injector was broken, I fixed the connection and the car started for 10 seconds before cutting off. Unplugged the MAF and it would idle rough for a long time. Then discovered leaks and positive pressure in the crankcase. Cleaned the PCV system (issue seemed to be the fully clogged vacuum line.) and the car idles with no leaks. Cleaned the MAF sensor also. At this point the car starts and runs with the MAF plugged in. Runs good from 2-4k rpms. When idling it seems to try and find the proper rpm but when it dips to 900-600 ish rpms the car runs real rough and sounds like an old diesel starting on a cold day or stalls. Will start easily but often stalls 10 seconds later when rpms drop. Any ideas what could be causing this?

clintnesbit · Post by **clintnesbit** » 13 Jun 2024, 01:01

I think a faulty fuel pressure regulator can cause issues with fuel delivery, leading to rough idling and stalling. Test the fuel pressure and ensure it's within the specified range. If it's too high or too low, you may need to replace the fuel pressure regulator.

Post by **volvolugnut** » 13 Jun 2024, 08:21

I think this model may have three adjustments that someone may have messed up.
There may be an air bypass adjustment knob under the throttle body. It would have a knurled black plastic knob. Turn in to decrease speed. Adjust for 700 Rpm. It may need disassemble and cleaning.
There is an idle mixture screw (it may still have the anti-tamper button on top) on the side of the air mass meter. This can be tested with a dwell meter.per the manual.
Three is also an adjustment to the throttle switch at the throttle body. The switch should make a click sound just as the throttle is starting to open. Do this with engine off.
The throttle body may need cleaning with carb cleaner. The idle speed control may also need cleaning or replacement. Idle speed is electric feedback controlled.
An inexperienced shade tree type mechanic may have adjust one or all of there in attempts to repair. They must be returned to proper settings for good idle. Directions are too detailed to give here. Try to find a manual like Bentley Publishers for the information. You have made great improvements. Keep going.
volvolugnut

Post by **volvolugnut** » 13 Jun 2024, 08:23

Fuel pressure should be 36 PSI. Test with gauge at the fuel rail.
volvolugnut

Post by **volvolugnut** » 13 Jun 2024, 16:59

After my last post I realized the original post was Jan 27, 2024. That was also the last time the original poster was active on MSV.
I suspect he is gone forever.
I hope the Volvo was saved.
volvolugnut

mrt740 · Post by **mrt740** » 22 Jun 2024, 15:22

Still here. Solve some of the issues. Wonk fuel lines and Chinese fuel pumps with missing O-rings were likely causing a lean condition. I replaced everything from the in-tank pump to the fuel rail. Makes 43 PSI at the rail. No experiencing a hunting idle when in park. It will stall or nearly stall then jump to 1100-1200 rpms. When put in gear it sits at a steady 750 rpms. Also experiencing severe hesitation between 2-3k rpms. With the pedal to the floor the car sounds like it misfires once sometimes a bunch of times and then suddenly revs smoothly beyond 3k. Cleaned IAC and it buzzes with key in 2 position.

Gong to start a new thread with this info as well.