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Vehicle is a 1990 740 GLE 16-Valve B234F red block engine, USA market (non-Calif), LH-2.4, head was rebuilt a few thousand miles ago after a snapped Timing Belt and bent valves. Repair work was done by local machinist, owner re-installed head and was his (not mine) daily driver for awhile. Issues started 2 years ago, lots of parts changed then and was back-burnered till now.
Symptoms: Idles perfect, low speed and high speed RPMs great, but engine hesitates badly in the 1,900 to 2,100 RPM range. -almost like there's a rev limiter kicking in and preventing it from passing the 2,000 mark. Tach shows a drop in pulses and reads a lower-than-actual RPM when the limiting is occurring. (I.E. You can hit 1900 rpm and then hear the hesitation and tach drops to 1700 but engine is still turning at 1900.)
Of note, disconnecting the Air Mass Meter causes the hesitation band to move up to 2100 to 2300 RPMs, and I have no idea why. The car can be driven with a light foot, you can slowly work up through the gears, then a forced detent downshift can jump you over the hesitation threshold and then you're in the upper RPMs with no problems. Overall, she seems to perform weaker that I would expect for a 16-valve, and seems similar to my 8-valve 240.
Known parts changed or tested and associate comments and questions:
1. RPM sensor (white band), was changed with another used RPM sensor (white band) that was available. It was one left over from preventative maintenance on my friend's car, and we seem to have a shortage of new sensors at the moment. (will have to order more)
2. Ignition Computer (Bosch 0227400152) replaced with a salvage-yard-special of identical part number. No improvement. Still have original on hand.
3. Fuel Injection Computer (Bosch 0280000571) briefly swapped during testing two years ago, but I don't know what he swapped it with. It could have been an identical one, or one that someone advised was compatible. Either way, he didn't notice any improvement. I want to swap it again to rule it out, but only have some spare 561 and 951 ECUs (of the LH-2.4 flavor) from 240s in my basement. Does anyone know if they are compatible and can be swapped for testing purposes?
4. White fuel injection relay, black Radio Suppression Relay, both swapped previously.
5. Ignition Power Stage (black box on the aluminum heat sink, name escapes me right now) also was swapped previously, no improvement.
6. Ignition coil also swapped, no improvement.
7. Air Mass Meter, swapped with no improvement. When disconnected it transfers the hesitation band from 1900-2100 rpms up to 2100 to 2300.
8. Knock sensor, swapped with no improvement. Ran with knock sensor disconnected in driveway tonight with no change either.
9. Instrument cluster, car ran with cluster disconnected during previous testing, no change.
10. Fuel pressure regulator previously swapped, no change.
11. Throttle position switch swapped previously, no change then. Ran it tonight with it disconnected and also observed no change.
I'm running out of ideas and options and thought I'd post this issue out to the Brickboard community to see if anyone else out there has any ideas. I'm also running out of time. The owner gave up troubleshooting two years ago, car sat till now, and he desires to get rid of it in a matter of days (via local scrap crusher which is paying top dollar right now).
There is one other possibility of hope, and that comes from another B234F owner in the area who is hoping to drive to see this car in the next day or so. Car #2 has an idle issue (aprox 1,300 and more) when warmed up, but fine when cold. That second owner hopes to swap some parts (ECU, IAC valve, etc) with the first vehicle mentioned above and we'll see what problems migrate from vehicle to vehicle. I will not be there when this testing happens (work hours) but hope to hear positive results.
Does anyone out there know if there was an RPM limiter on the B234F engines? (I'm pretty sure yes.) If so, was it done via Ignition control or ECU/fuel control?
I did not pull any OBD-1 codes tonight as the owner advised me there wouldn't be any, except for the ones we would cause (I.E. disconnecting the knock sensor, etc). Does anybody know if there is a way to use the Volvo Tool 5280 (the home made Test LED Light) on the ignition system to get real-time data from it? I looked for a Yellow-Red wire next to the Pink remote start wire and didn't find one.
Any thoughts, advice, or information would be greatly appreciated.
God bless,
Fitz Fitzgerald.
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'87 Blue 240 Wagon, 376k miles.
'93 Green 240 Wagon, 230k miles.
'88 Black 780 Coupe.
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