Small problem

[speednut]

Hi all,
I hope someone can give me an opinion one this . While I was on my trip to Wyoming from my home in Va (nearly a 5000 mile round trip) my afr's would drop from maybe 13.7 to 12.8 for seemingly no reason when I would accelerate lightly. Which is o.k. but when I went back to a steady cruise the afr wouldn't go back to my 13.7 it would stay at 12.6 or 7 ? It always use to return to a normal cruise afr ,what might cause that? And one other point,if I put it in neutral when this happens, shut the car off, turn it immediately back on, put it back in high gear , all returns to normal(I do this while still going down the road) Till the next time I accelerate lightly.. My normal afr on cruise is about 14.6 or 7 , elevation changes things especialy at 6000 to 10000 ft.. OH !! 1987 930 disconnected o2..


thanks for listening !!!!

[JFairman]

Check and see if your rear fuel pump is running. My '87 will run steady cruise speeds fine with just the front pump running.
If the rear fuel pump is not running it's often the rear most fuel pump red relay gone wrong. They don't last forever...

The WUR/control pressure regulator and cold start auxilliary air slide valve bimetalic spring heater elements get their power from the rear fuel pump relay and if they don't get power from the relay the WUR bimetalic spring will cool off and lower control pressure and make the AFR go richer, and the auxilliary air slide valve will also cool off and will make the idle speed go higher as it bypasses air around the throttle body.

If thats not it than maybe the WUR or fuel head needs some attention.

[speednut]

Thanks ! I'll check the pump and the relay . Are the relays serviceable or throwaways? Why does it do it when I accelerate...almost always?

[smurfbus]

Maybe the rear red relay (in the front trunk) heats up of more current to run the pump on acceleration (more flow, same pressure) or the red relay is not very tight on the socket?

[mark houghton]

Mine started doing something similar awhile ago...I just haven't bothered yet to troubleshoot. I can run her down the highway for a half hour, get nice and warm, with AFR's keeping steady at around 14.2 and responding normally on boost with appropriate AFR's. Then, come into town for some slow driving, maybe shut her down for a few minutes to run into the store for some refreshments, then back on the road...only to find the AFR's dropping on moderate throttle acceleration. I'm talking down to like 12.5. Not normal. Figure I'm heat soaked by that point and something is changing....perhaps losing some air past an o'ring that's slighly dislodged and only gets worse when hot.
WUR has maybe 2000 miles on it since BL did his thing, so I doubt that's it. Most likely fuel presure dropping off. Thought maybe I was losing power to the WUR heating element, but why waiting until she's nice and hot?
Jim, you may have a point there with the rear pump relay doing the funky chicken. That could explain a lot. May have to look into that.

[mark houghton]

Originally Posted by speednut

Thanks ! I'll check the pump and the relay . Are the relays serviceable or throwaways? Why does it do it when I accelerate...almost always?

Supply and demand. If one pump is not working then not enough fuel pressure resistance against the metering plate/control arm, allowing it to deflect too far as intake air flows across it; thus it meters too much fuel to the injectors in relation to the amount of air taken in. In theory, anyway.

[speednut]

Hi all

I think the red relay may very well be the issue,I swaped it with a different red one and things seemed better but I didn't get a

chance to drive it as long as I wanted to...Iv'e been trying to get the AC chillin, It's been close to 100 !!

thanks

[Dave 86 930 Fl]

Originally Posted by speednut

Hi all,
I hope someone can give me an opinion one this . While I was on my trip to Wyoming from my home in Va (nearly a 5000 mile round trip) my afr's would drop from maybe 13.7 to 12.8 for seemingly no reason when I would accelerate lightly. Which is o.k. but when I went back to a steady cruise the afr wouldn't go back to my 13.7 it would stay at 12.6 or 7 ? It always use to return to a normal cruise afr ,what might cause that? And one other point,if I put it in neutral when this happens, shut the car off, turn it immediately back on, put it back in high gear , all returns to normal(I do this while still going down the road) Till the next time I accelerate lightly.. My normal afr on cruise is about 14.6 or 7 , elevation changes things especialy at 6000 to 10000 ft.. OH !! 1987 930 disconnected o2..


thanks for listening !!!!

I had a similar problem and I determined that my fuel metering plate was oscillating, which was causing the lower AFRs. I sent the fuel head off for a rebuild and the problem is solved. I was able to reproduce the low AFR situation in my garage with the air cleaner off and that is how I recognized that the metering plate was vibrating ... I'd suggest that you try the same test.