im having a hard time with this one
the car idles fine but once put in drive and try to drive it starts to backfire
if i give gas slow it gets up to speed with litle hesitation
its a 86 928s 5.0l
can anyone help me pleaseeeeeeeee

 

This is a new one. And this happens w/engine warm and cold? OAT? Does it clear at speed? As stated the problem sounds undrivable?

I'm guessing EZK related, but not sure where to go from there. Timing cams check OK? You've looked thru the vents on top of cam covers and cams are where they should be? TB warning has not come on recently?

 

Use a good light and check the distributor caps and rotors inside and out for any cracks or carbon traces. Check the plug wires for spark jumping from wire to wire.

If you have removed or replaced the plug wires, you have a pair in the wrong places.

 

I've cleared one-such problem on 86 with exactly what Wally suggests, rotor/cap cleaning.

Have another with an 85, same as you describe, and its driving me crazy. Oscilloscope on its way from Jadz928 so I can finish through the 85/6 diagnostic test plan, as the easy stuff is already done. Although, I could have a bad new wire, considering I used the economy set and reused ends. Hmm.

 

thanks for the info guys
tommorow morning im doing the timing belt on it so il check caps and rotors
il keep posting what i find

 

Sounds like it could be a very weak mixture. Try to set idle mixcture as per the WSM.

 

ok got both ign caps off and everythink looks nice and clean inside
both rotors look fine two will finish timing belt job tommorow
and i will check for wrong ign wires
as far as the mixire goes how to adjust that and to what limits?
forget to mantion someone was working on this car for a while now and all the vacuum hoses look change but i dont know if thet are in the right order
Do both fuel dumper valves need vacuum at idle?

 

You need to have a copy of the Workshop Manual. It is available on CD-ROM (the Jim Morrehouse version) from Roger Tyson at 928sRus, a sponsor of this site.

 

If anyone has touched the plug wires, spend the time to very, very carefully check their placement...

 

another question. i got the timing belt off the car when to instal new one and i notice that the black boot at the end of the tensioner is broke. i order a kit for it for monday
now for the question at the bottow left side right next to the crank shaft there is a litle pully that is very hard to turn is that normal?

 

You probably need to have your MAF rebuilt. Try borrowing one to see if that is the issue. They are the same, 85-95.

If you upgrade to a PKsn'r, you won't need that pulley...

 

It should turn.

Did you order new tensioner bolt and bushings for it and new rollers and gears like the crank gear and the oil pump gear?

How about tensioner measurement tool?

 

i did order a tentioner rebuild kit

 

can somebody tell me what is that litle pully to the left of the crank shaft?

 

Tensioner Pivor bolt?
Tensioner Pivot bolt bushings? Not part of a kit unless specifically defined as such.

That is a safety guide wheel/ idler.
Some remove it. I do not. You can press-in a new bearing.