Tech Forum : bumps in road makes engine stumble.. ideas?

jesse	Posted Monday, Oct 15th 7:14pm [Edit] [Quote] [IMS] [View car]
Member Post nr. 397 SF, USA Dinan 1978 333i, honda insight, audi S4	It seems that when I hit bumps in the road, significant ones, the engine stumbles about 1/2 second later each time. It almost dies for a second and gets bumped back to life by the momentum etc... It feels like it's either losing spark or fuel. I am suspecting something electrical. I wiggled all the plug and coil wires at the rotor and they seemed to be on tight. I guess next I'll check the injector wiring. Oh, just had an idea, to hook up the split second box I had to put a new relay in for the fuel pump, possibly it's got a lose connection that toggles the fuel pump off for a split second and that's why there is a delay from the bump to the stall. Jesse

Remuxer	Posted Saturday, Nov 3rd 11:02am [Edit] [Quote] [IMS] [View car]
Member Post nr. 13 Atlanta GA USA 83 320i	Had the exact same problem, turned out to be a loose wire on the underside on the fusebox. This isn't deficult to check or repair but will take patience and an annoying amount of atttention to detail. Carefully undo the rear wiring harness connector on the fusebox and rearside fusebox relays, then undo the nut on the one stud holding the fusebox to the frame, flip the fusebox upside down in place and begin checking everything. Definetly check the underside of the small bolt who's head is visable from the topside of the fusebox. On the bottomside of the fusebox that bolt connects the main 12V feed wire from the battery to the 12V aluminum rail that essentially feeds power to all of the relays and fuses as well as other important stuff. The feed wire is red and has a ring terminal on it. After a long or bumpy ride it can get loose and cause havoc! (mine was caused from a 1400 mile trip through the appalacians) -because it is a large ring around a small bolt If it loosens, the electrical connection will go in and out with the bouncing and gear shifting of the car. It can also arc onto adjacent circuits causing ignition weirdness. When the car is idling, or riding smoothly this problem will not occur because gravity pulls the ring terminal against the nut and bolt. A portion of my fusebox was melted from the high resistance the 12v had to overcome from the poor connection. -and while your down there clean and re-spring the push-fit terminal connections. If you have to replace a bad pushfit you need to use an exact replacement as the BMW pushfits have a tension guide on one side which keeps it locked in place. Aftermarket auto store terminals often will not work reliably. Keep the row of 30a relays pushed in while you work on the pushfits -this way the you are sure the pushfits are properly tensioned onto the legs of the relays Also keep careful track of any wires you disconnect. Absolutely don't rely soley on the North American BMW wiring diagrams. They are incorrect in many places due to model variations, compliance additions, and options. -Off the top of my head I can tell you the Load shedding relay on North American E21 BMWS came to America wired differently than what is on the diagrams. If you have any problems I can send you some wiring deviation info. Good Luck.

jesse	Posted Monday, Nov 5th 6:34pm [Edit] [Quote] [IMS] [View car]
Member Post nr. 403 SF, USA Dinan 1978 333i, honda insight, audi S4	Thanks for the well thought out response Remuxer. I think you are barking up the right tree since a local guy once had the exact same problem on his e21 and when I told him about the stumbling he said he "fixed" it by somehow stabilizing everything in the fusebox so it wouldn't move when he hit bumps.... cause he didn't have to time to go through all the wires to find out which one was sketchy. Sounds like it was probably the same one you had problems with and I probably have the same. Either way it's really easy to check so I'll probably get to it this week and report back for the record. Thanks again, Jesse