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To be clear, yes, a North American US market 1988 240.
Before we go, the Bosch LH-Jetronic 2.2 fuel control and the Chrysler-MPG ignition are somewhat a mystery. I've learned by reading the service manuals usually when another 240 owner has an existential 240 crisis typically at a salvage yard. (Then my Bentley 240 service manual gets swiped in Spokane Valley.)
Innumerable resources exist for your edification here on this forum and elsewhere. You may want to learn auto motor mechanical and engine control (fuel injection, ignition, and emissions) operation theory and construction.
Mighty and powerful Art Benstein reminded us 240 uses batch injection; all injectors open and close simultaneously, if injectors are in fine shape, meaning fuel flow halts when power is off. Occasionally injectors leak as one or more may not fully close. Exclude the cold start valve injector from batch injection though these can leak also. You do not complain of a gasoline odor in the engine bay.
When the intake manifold vacuum is high (negative pressure if you will), your foot is barely pressing or is off the gas pedal, less or minimum fuel is injected; fuel control reduces injector open duration.
A fully pressed gas pedal reduces the intake manifold vacuum. A working FPR raises the upstream fuel pressure with reduced manifold vacuum.
Of coursed you have resolved no other vacuum leaks persist. With a vacuum gauge you can test for proper vacuum. Yet inspection can find vacuum leaks.
Do you know whether the air intake port manifold to cylinder head gasket has been replaced?
So, on to, in Benstein parlance, guessfest from the armchair. (Gets to use italics as if HTML 2.x+!)
Main problem for the past month:
poor gas mileage consistently and
intermittent (what, backfiring or hesitation?) when moving from stop or driving up to about 20 mph backfires then won't move for about 10-15 seconds, then takes off.
As with the term 'bogging'? The engine bogs or is bogging when accelerating
No problems with acceleration above about 20 mph.
To be clear, verify the throttle position switch (TPS) adjustment, or, if the exterior is fouled with engine oil grime and intruding into the TPS housing interfering with the copper switch contacts, or the TPS is failed in such a way as to allow idle control to continue as you accelerate. At 20 MPH, momentum of the engine and body eventually overcome an active idle control. Normally, once you press the fuel pedal, so the TPS clicks, idle control deactivates as you control engine action through the gas pedal (and many other controls). Idle control returns as you release the gas pedal. Haynes, Bentley, Volvo green factory manuals, and I guess Clymer treat the TPS topic well. So does the Volvo 700-900 FAQ here where you test sensors using your electric digital multimeter.
You've been here:
https://www.brickboard.com/FAQ/700-900/ElectricalIgnition.htm
'Cept 240 is the only model equipped with the Chrysler-MPG ignition in the engine bay hanging on the washer fluid reservoir basket frame. To be clear, other resources exist that may include this information, or at least a wiring diagram:
http://www.v8volvo.se/mekartips/volvo/index.html
Find a green factory manual (not quite the now gone k-jet.org):
https://ozvolvo.org/archive/
Instruktionsböcker Volvo 140/164/240/260
http://www.240.se/litteratur/instbok.htm
Search Bing and Google to find the TP number for the listed artifact. May find it in the Oz Volvo archive. Since Chinese ownership, Volvo Cars AB is shutting down these valuable resources.
The mess that requires you to use Adobe shockwave player plug-in, if your browser allows it.
http://www.volvotips.com/
Web pages here may have PDFs yet more often have PDF files converted to low-resolution shockwave files. I use the uBlock Origin ad blocker on Mozilla and Chromium browsers as the adverts are noxious.
And on facebook, try:
Volvo 240 fan club
https://www.facebook.com/groups/Volvo240Club/
Volvo 240, 740 and 940 owners club
https://www.facebook.com/groups/23765538560/
Exhaust smells horrible; I can't describe well, maybe gas, but it's definitely not rotten egg smell. There's no smoke that I can see.
Rotten egg smell on a catalytic converter equipped exhaust is a clear indication of a rich fuel to air running condition. How to you drive it? Or how do you drive? Short trips are awful for 240 (We can say RWD Volvo) as the exhaust, specially catalytic converter, the condition, if persistent, means your catalytic converter is deteriorating. Restore proper tune and the catalytic converter may clear as it heats up. As with daily round trip drive to work with hopefully some freeway run time. Proper use allows the exhaust to heat up and, sometime there after, the coolant, and later, the engine oil fully heats. Have I written this in a prior response to you in your prior posts?
Proper tune exhaust is sweet and 'dry' though may produce steam during warm up or on cold days. Though a damp never dry exhaust may suggest coolant leak, yet smell sweet yet more so smell like coolant with a head gasket failure.
How does the exhaust smell terrible again? Not rotten egg sulfur yet not gas smell. You do describe a rich fuel to air ratio the engine eats.
Someone suggested that my piston rings might also be leaking oil.
You mean the piston oil control rings in the engine, yes? My piston oil rings sounded like you have a set to install?
Oil control rings limit oil intrusion into the combustion chamber on the downstroke while the two compression rings limit compression blow by into the engine oil sump spaces
You have performed a compression or leak down test? I made mention in a prior response in one or more of your many threads and posts on same or similar issues.
inside the distributor cap is oil, but not outside it. I checked FAQs about the distributor, am unclear, and wanted to talk doing this out for my first time so that I don't botch the repair:
https://www.brickboard.com/FAQ/700-900/ElectricalIgnition.htm#DistributorandShaftSealReplacement
This information is for behind the head 700-900 series Bosch distributors. Though similar. Not yours.
If Chrysler-MPG, your engine will come fitted with the Chrysler distributor. Though there may be later models with a Bosch distributor.
Since the oil is inside the distributor, I would need to replace the smaller o-ring, but should probably replace all of them?
On Chrysler and Bosch there is a large O-ring in a groove that seals against the bore and the groove the distributor. It has been a long time I've pulled and serviced a distributor.
On both there is a bushing / seal that fixes the rotating shaft with the gear into the outer stationary outer distributor shaft. The bushing can wear. It is lubed by splash oil yet oil should not intrude (much if at all) the space with the impulse sender / rotor / and the cap underside. There may be a plastic guard in opaque, grey, or black that sets along the top rim of the distributor housing rim with a tab to align at the keyway the distributor cap secures into. Yet you may have a Bosch distributor in 1986-1988 here:
Volvo 240 Bosch 0287520004 Ignition Distributor 86-88 OE 4-cyl Hall Sensor Style
Bosch PN 0287520004
https://www.ebay.com/itm/Volvo-240-Bosch-0287520004-Ignition-Distributor-86-88-OE-4-cyl-Hall-Sensor-Style/303079625259
You see the condesation barrier cap thing to the right in the first image.
As you have oil intrusion in the distirbutor, and the PCV is breathing clearly, you may need to buy rebuilt or new. You may be able to rebuild it yet Bosch parts availability ....
As for how to remove, it is a snug fit. Realignment on reinstall requires the rotor point to a raised mark on the housing rim, and that aligned with a place or mark on the block. I'll let you research that.
Find the Bosch large o-ring for the outside of the distributor housing shaft from Bosch or Volvo.
I'm not all that familiar with 1988 and older up to the final non-turbo K-jetronic. So, many others will provide correction here.
I was also doddering on the facebnook groups, trying to bring them to the brickboard. Been exhorting the facebook Volvo group users to come here and join the brickboard and turboricks since 2011. Maybe this is working>? I dunno.
I'll look at your Update later.
What was a warm-up became another novella.
Questions?
Mac Dud.
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