View Full Version : 1990 750IL backfires, surging on highway... help?

10-30-2005, 08:42 PM
I recently bought a 1990 750IL that came with a backfiring problem... my very reliable BMW mechanic has been unable to address the problem, we put new plugs, plug wires and dcap on it... no fix...

The nature of the problem, once the car's warmed up, when I'm driving the vehicle, if I accelerate and then let of the gas, it starts backfiring (popping sound in the engine compartment)... I'm going to take it to the dealer to address (to run the error codes)... in addition, the check engine light comes on when this is happening, when I tap the gas, the check engine light turns off.

Additional messages show up when I turn the car of CHECK OIL PRESSURE SENSOR and powersteering fluid low (but is full)... if anyone has some answers to this problem, I'd love to hear them before I start pouring money into dignostics... or replacing things that don't need to be replaced...

Thanks for your input in advance.

10-30-2005, 09:33 PM
Well, first the easy things:
Oil pressure sensor can be easily exchanged. Maybe you buy it from www.autohausaz.com
I usually buy from them as they have a good service and decent prices. But compare with others too. Do a search here for BMW online vendors list (see top of this page the search).
Power steering fluid low: as you have a 750 iL, this one has LAD. And the LAD system and the power steering have the same fluid system, and they use Pentosin CHF 7.1 in your case (see sticker on top of it). That reservoir has NO dipstick to check the level. How did you check it? Which procedure did you make before checking level?

If you have a U.S. specification car, you can make a socalled stomp test, which will give you some numbers on possible faults. Pls visit my website below and see the procedure for stomp test and let us know the numbers you got.
Easier it will be, if you buy a PEAKE fault finder, www.peakeresearch.com

You also say check engine light comes on. What faults are stored in the check engine and are displayed? You can see the results on the CC. If not , see the owners manual how to get them. If you do not have an owners manual, see my website below and download it from there.

Let's see what you find out and then tell us, we can help you.

10-31-2005, 10:05 PM
is it possible the problem could be something as simple as not having enough backpressure in your exhaust? maybe there is a leak.. or maybe your muffler is shot..

backfiring is common on sportbikes with aftermarket exhausts.. after a while the can(muffler) gets empty and has to be re-packed. major backfiring