m30 535is issues

Specific conversations and info for the BMW E28 M5 and M535i.
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Janelle
Posts: 3
Joined: Sep 04, 2020 1:09 PM
Location: San Diego

m30 535is issues

Post by Janelle »

I have been trying to get my '88 535is running and on the road. I need to pass california smog to get the title. The car had been sitting for ~3-4 years. It was a car my mom left to me when she passed away and I'm really sentimental about it. I found it for her originally about 11 years ago. When I started working on it recently, it had low compression in the 70-80psi range and was backfiring through the intake. I had found the timing chain had slipped, so I took the front timing case off and replaced the tensioner and the missing timing guide rail and corrected the cam timing to TDC. I ended up putting a new water pump, thermostat, distributor, rotor, battery, and fuel line to the 7th injector which poured out fuel into the engine bay. I drained most of the fuel and poured in ~3 gallons of good fuel. There is a possibility there is still some bad fuel in it. I cleaned all the fuses and the terminals on the fusebox.

It starts and idles great. If I lightly press the gas pedal it bogs and almost stalls. If I press it a little harder it backfires now through the exhaust. It never revs over ~2.5k rpm

I've checked the throttle position sensor with a multimeter and it seems to be behaving correctly. I think the AFM was replaced in 2016 but I'm not certain (it does look pretty clean). I don't exactly want to keep throwing parts at it, but I'm kind of stumped on what to do next. I plan on getting a fresh pair of spark plugs, but I'm not looking forward to potentially doing the ignition cables or coil. I was planning on looking up how to test them first at least. My thoughts are that it could be O2, 7th injector, fuel pressure, or bad fuel. I don't see any vacuum leaks but I could be missing something. I only have a backyard mechanic level of tools, and I'm on a pretty tight budget at this point since I spent a lot of what I budgeted on the other repairs so far. There is no check engine light on.

Is there anything I'm missing? I wanted to look into the motronic troubleshooting guide but I dont know if its 1.0, 1.1 or 1.3
topher800
Posts: 318
Joined: Nov 24, 2009 10:44 AM
Location: Boulder, CO

Re: m30 535is issues

Post by topher800 »

You should move this over to Tech Talk. Your car is not an M5 or M535. You will get more eyeballs over there.
ahab
Posts: 6109
Joined: Jun 11, 2006 9:12 AM
Location: Chalfont, PA

Re: m30 535is issues

Post by ahab »

There is no check engine light at all on these cars. The Motronic is M1.0a, M1.0 with an O2 sensor which makes it adaptive. My guess is you still have the timing off by a tooth or two. A bad CTS or AFM could also create similar problems by dumping too much fuel but excessive backfiring on a cold car usually means spark is happening when it's not expected to. Fuel is getting ignited by an errant spark as it's passing through an exhaust valve. Recheck compression too. If anything got bent when the cam chain jumped you could have a bent valve which would mean the cyl doesn't seal and combustion could be getting into the exhaust that way.

Piston TDC occurs twice on these engines for every combustion cycle. make sure you're not 180° out. The locating dowel on the cam gear should be at ~7 o'clock, if it's at 2 o'clock you're off by a rotation. Another way to verify is that the cam lobes on cyl 1 should be pointing downward, equidistant from the centerline of the cam. Not sure it would run at all that way so I think a tooth is more likely.

Before buying new plug wires, ohm these out. They should be in the 5,500-6k range, give or take. Anything wildly out of spec means a problem with the wire or the insulator. The wires themselves are braided stainless and rarely go bad. Shake them when the meter is connected to ensure there aren't any flakey connections inside.
Janelle
Posts: 3
Joined: Sep 04, 2020 1:09 PM
Location: San Diego

Re: m30 535is issues

Post by Janelle »

Sorry, I didn't realize this wasn't the right forum for it.

I did the resistances on the plug wires and got ~28k across all wires, and 26k at the coil wire. I also swapped spark plugs and cycled the rest of the bad fuel. Spark plugs I put in have a resistor in them, they were the standard bosch ones the store had on file for it.

After the spark plugs swap it definitely seemed to idle with a bit more power, but still backfiring and unable Tod rev up. I am 95% sure I did the cam timing correctly. I did the compression check after doing the timing and all was good there also.

I tested the cold start injector and it's working correctly. I noticed that pulling the plug on the temperature sensor on the thermostat housing makes some difference to how it runs, even when the cold start injector was pulled out. I ordered a new one of these sensors. I also tested the TPS. I don't think it's the AFM because I think it was replaced about 4 years ago and it looks really clean, I don't know if there's a good way to test it.

Very possible that it could be the Crank position sensor, not sure if there's an easy way to test that without an oscilloscope.

Haven't tested o2 either, not sure if I can test that with my crappy multimeter.

Running out of ideas and I've already spent way more than I planned on 😔
ahab
Posts: 6109
Joined: Jun 11, 2006 9:12 AM
Location: Chalfont, PA

Re: m30 535is issues

Post by ahab »

While I don't think it's your problem, plug wires should ohm around 6k.

Does it smell rich? You may have a failed fuel pressure regulator so a fuel pressure test would be a good idea. If that's out of your scope, a new 3 bar FPR is about $60 and you'll have a spare if that's not it.

Coolant temp sensor in the thermo housing should be blue with two terminals. It should ohm out at 28k or so when stone cold and ~325 when hot. The Bentley has the exact specs, I'm just going from memory.

Crank position sensor, there are actually two on this car, and on the flywheel. The one on the harmonic balancer on the front of the engine is only for the diagnostic plug. However, if those sensors fail you end up with a no start/no run. You can ohm them as well, the spec is 940 across two pins and 0 across the other two (three pin plug).

Unlikely a bad O2 would create this problem. You can search this board on how to back probe the connector and see if it dithers. You may have a large green plug on the DME harness in the engine bay (near the glovebox) that is your O2 signal.
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