I'm new to cars, period. I'm a motorcycle guy. I've got lots of older bikes, none of which have emissions crap. my state doesn't have really strict emissions laws, so I can get away with almost anything. I've got a 91 240 wagon that has various assorted electrical gremlins that I can't figure out for the life of me, and why would I replaced 30 year old garbage electrical components with 30 year old garbage electrical components? is there a way to bypass things like o2 sensors, the cursed MAF sensor, and things like this that are required on newer vehicles in some states? this thing accelerates up to 45 like a 49cc scooter with flat tires. above 55 it's totally fine. people have been honking at me because it will bog down if I give it more than 1/3 throttle upon initial acceleration. I've thrown 3 MAF sensors at it in the last month. I'm getting tired of shelling out that money. something keeps fouling them. each time I replace one, it works fine for two or three days, then it goes back to turd mode. test it, it's a bad MAF. replace and hedge bets on when I'll need another. unplugging it makes it run worse. I recently blew out the tail pipe just before the cat (something else that I'd like to get rid of) after a particularly bad backfire, and it had absolutely no effect what so ever on performance.

 

well, you wanna go old school, strip off the entire fuel injection system, and replace it with carbs, you can get an intake manifold that fits these blocks from Volvo Penta marine, and mount a couple sidedraft SU/Zenith style carbs.

good luck with your fuel economy if you tune for performance, and good luck with your performance if you tune for fuel economy.


just curious, those MAF's you've been swapping... what brand and vendor ? lotta real junk in the parts market nowdays coming out of the far east. our 87 240 went a half million miles on its original MAF and ECU and injectors.... never a problem. we had to rebuild the transmission around 250K, that was the only major repair. a couple alternators, a few water pumps.... the a/c was dead, and some things like that. there's nothing upstream of the MAF butt he air filter, the PCV ('flame trap') is connected downstream so shouldn't foul it.

 

The O2 sensor you can leave unplugged, it's job is to slightly modify the mixture to make to Cat converter work most efficiently. If everything else works properly - the car should run OK.

Air mass meters last for years - Does your car still have the intake preheater pipe? The corrugated silver tube from the exhaust downpipe to bottom of the air filter? Check the thermostat in the air filter housing that goes bad and sends preheated air to the AMM all the time - and can damage it. It should change to cold air intake about 40 degrees. If bad disconnect the tube and remove the flap in the air filter box directing hot air to the intake - it if you live in a moderate to hot climate. Block the hot air intake on the bottom of the air filter housing with a piece of the silver tube crimped off.

Your lack of power/acceleration could be Cat converter related - the ceramic honeycomb wafer in the converter can break up and form in the shape of a ball - that will block the flow of exhaust when trying to accelerate. The ball rolls up the "ramp" at the back of the converter and blocks - like putting a potato in your tailpipe. Tap the converter, any rattling sounds? Take the converter loose and look inside, if there's loose stuff, break it up and dump it out.

As others have said the AMM is a reliable part. I would avoid off brands and allegedly "rebuilt" units.

 

What codes are stored in the control units? (the 6 port diagnostic box under the hood) - Do you know how to use that? The system self tests many components and sets trouble codes in the ignition and fuel system control units. Takes less than a minute and only your finger is needed to check codes.

If the car runs worse with the O2 disconnected (and hot engine) - there is something wrong with the basic fuel delivery. You can use the voltage from a working O2 sensor to roughly test the fuel mixture - unplugged you should find between 0 and 1.2 volts coming from the o2 sensor with the engine running. Normally at idle should fluctuate from .2-.8 volts. 0 volts is too lean, 1.2 volts is too rich.

If you have a backfire in the exhaust - that comes from excess fuel, way too much unburnt fuel in the exhaust system. It can only get there from the 4 injectors or the fuel pressure regulator. (or rarely the pcv system or charcoal canister). How about a broken/leaking diaphragm in the fuel pressure regulator? Take the vacuum hose loose with the engine running and look for gasoline - there should be none. Or too high fuel pressure (not common) - or an injector that's spraying all the time, or leaking slightly. I should mention I have seen engines with a oil/gasline mixture in the crankcase - due to a bad fuel pressure regulator or injector problems - so if your oil level goes up instead of down and smells funny -

If it won't accelerate you could have low fuel pressure - there are two fuel pumps, the feeder pump in the gas tank can/does go bad and make the main pump under the drivers seat work harder, eventually causing low fuel pressure and poor running, usually worse after the pump heats up and/or with lower fuel levels. You should check fuel pressure.

By the way a bad AMM was one of the most misdiagnosed parts my techs would come up with - I always had a new one on the shelf to test with, and If I sold an AMM we kept the old one on the shelf with the customers name and date on the box. There were many times I refunded, reinstalled the old AMM and then found the REAL problem.

 

Sounds like you gotta a cheap MAFS problem. Get a good one!

 

there is no preheater on this, or at least not an obvious one. the tail pipe exploded just before the cat, so it's not choked off there for sure.

 

without the MAF sensor plugged in, it backfires like a pulsejet at highway speeds, on deceleration. it does not do this with the MAF plugged in, good or bad. i've already stated that these problems go away upon replacement of the MAF sensor. they keep failing. I understand that it's probably a wiring related issue. I'm not going to rewire this brick of coke on wheels. I've already replaced both fuel pumps. fuel pressure is just fine. I checked when I replaced the pumps for clogs/etc.

 

cheap, my ***. these things are upwards of 180$ from Delphi.

 

so you measured 43 PSI +/- 1 PSI with the vacuum line to the fuel pressure regulator disconnected?

 

not me personally, I had my local shop do it when they installed the new filter/pumps and flushed the tank. I'm not completely inept here, I just don't have the space for working on my car like I'd like to. I work on my bikes in my living room for cryin' out loud. I also apologize If I came off as rude the first time, that wasn't my intent. frustrated at this car haha.

 

Just one more thing...do you have an aftermarket, oil and paper air filter? K &N is the most common brand. If these are over oiled (which is easy to do) they can cause the heated wire in the middle of the AMM to become dirty and give drivability issues like this. Also, the warm air intake thermostat is easily defeated by putting in a screw so that it doesn't open; useful tip in California, where the lack of the warm air pipe will cause a fail on the visual inspection portion of the smog test.