Hey guys -

My '85 240DL (well, my son's, but I'm the one trying to figure out what's wrong) is getting lousy mileage. About 11 mpg.

We've only had it a couple of months, and my Volvo experience is limited to a '70 144 and a '63 122S, so this car is bit of a different beast.

As far as a troubleshooting list, I understand an O2 sensor and tune-up are my priorities.

Any other suggestions (Pierce, are you out there)?

Thanks !

- Mike

 

85 is early LH 2.2 injection, pretty simple stuff.

I dunno, I think I'd do a visual inspection of everything important (air plumbing especially), verify the fuel pressure regulator isn't leaking (disconnect its vacuum hose, if there's gas there, its bad). check all the vacuum lines.

check the ECT (engine coolant temp) sensor resistance with a multimeter, when its hot and cold. if the ECU thinks the engine cold, it will run very rich. I usually test it at the ECU connector. any problem is as likely to be wiring as the actual sensor. the ECT is one of three sensors under the intake manifold on the engine.

if the o2 sensor is ancient I'd replace it on principle, its easy enough. they last at LEAST 60k miles as long as the car is running correctly.


pull the spark plugs, they are probably black because its been running way too rich. do a compression test to be sure the mechanical part is good. install new bosch or ngk copper plugs gapped properly, bougicord wire set, bosch cap & rotor. LH 2.2 is timed the old fashion way, via turning the distributor... there's a hall sensor in the distributor, its wiring can get bunged up, but that causes no starts, not rich running.

 

Thanks, Pierce !

What really has me stumped is that it starts and runs fine.

I'll run through your list and see what happens.

Cheers,
- Mike

 

I'm putting my money on the ECT then.

here, read this page.
http://www.swedishbricks.net/700900F...eSensors1.html

You have LH 2.2, much of that page is talking about LH 2.4 (1989+) but the ECT is exactly the same. a 240 has a different ignition system than the 740/940 EZK but it works basically the same.

the ETC has 2 resistors to ground, one for the ICU and one for the ECU... the values of each resistor should be 6K ohms at freezing (32F, 0C), about 2.3K at 68F(20C) and 200 ohms at boiling (212F, 100C)... so what I do is... pop off the access panel for the ECU, drive the engine til its fully warmed up, unplug the ECU connector, and ohm the correct pin to a ground pin.... wait a few hours til the car is at ambient and read it again.

if its open circuit, the ECU will think the engine is really cold, and dump in extra gas.

oh. question: how is the throttle response when its driving? can you floor it and does it go OK? a B23/B230 engine is about 110HP and should be able to zoom right off the line in 1st, and wind up all the gears. sure, above 60-70 MPH the power is meh.

 

if the throttle is lagging badly, then it might be in failsafe mode, and you might have a bad air mass meter (MAF/AMM). with the car off, unplug the AMM, and start it, if it drives the same, thats a very good sign the AMM or its connector is bad. shut it off before plugging the AMM back in.

 

Thanks again, Pierce - much appreciated.

The throttle response while driving is fine. No lag, plenty of power in city driving, and no stumbling or idle issues.

I'd suspected the MAF as the culprit, and the O2 sensor looks new, so I thought I'd troubleshoot cheaper possibilities first.

If I can pry the car away from my son today I'll investigate the ECT and let you know what I find.

Again, much obliged, Pierce.

Cheers,
- Mike

 

Any exhaust leaks upstream of the O2 sensor can also reduce your gas mileage. Check the downpipe for any leaks in there.

 

Hey Pierce - Just had a chance to install the coolant temp sensor, so we'll see what happens. The old one had some low resistance readings for ambient temp, so that was probably the culprit.

Thanks again for the help!

Cheers,
- Mike

 

Thanks for the tip, act1292, I'll have a look ...

 

The link says to test the ECU plug wire #13, Bentleys says that goes to the fuel injectors and the coolant temp sensor is #2 wire for a LH2.2.

 

yeah, sorry, I should have clarified, the pinout is different.

 

airleaks: check with hose in your ear. remove and inspect intake hose. , MAF, o2 sensor, coolant temp (maybe), timing, compression, do a leakdown test, intall bougicord wires and bosch cap rotor, fresh oil and fuel filter, make sure tank pump runs,