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My '86 Bosch fuel injected Spider has run too rich, starts and idles poorly after installing a new exhaust system: headers, new mufflers, twin Ansa pipes; and after installing new high lift (11mm) cams. My mechanic suggests that the ECU is overwhelmed by the changes, and that the next step is an Engine Management System (he likes Haltec) that puts the Spider on a dynamometer to dial in improvements. He's checked both the intake air hoses for leaks and the FI water temp sensor, and they're both fine. Has anyone gone this route?
Thanks
gdm
 

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the ecu shold be able to handle these changes( mosly cam size,) exhaust has nothing do do with running rich.. new o2?
 

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Most owners of modified cars find that the stock system is not able to keep up with increased fuel requirments. But that wouldn't explain why it would run rich.

Did you (or the mechanic) check for proper functioning of the O2 sensor? When the O2 sensor gets old (say 60-90K miles) they can get lazy. The ECU interprets that as an invalid signal and then ignores it and instead uses its default (slightly rich) map.
 

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a note, i am going to be going to bigger cams, and other mods.. my freind who doe's bmw's says the stock ecu can handle the changes, just need to get 20 lbs/hr injectores, stock are 16 lbs/hr..all the ecu doe's is fine tune the mixture( with help from the o2 sensor) and time injection lenght....just checked on the air flow meter on a 84 spider, and a 6 cly bmw.. same size air flow meter( the flap)
 

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I've been struggling with an S3 that has run rich since I got it 5 months ago. I replaced the O2 sensor, but that didn't help. I've come to the conclusion that the PO may have adjusted the AFM (perhaps to get more power). Last night, I adjusted the AFM wheel five notches clockwise to see if it leans out the engine any. The car ran well after the adjustment, but I haven't done any testing to see if it is running less rich.
 

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Presuming the cams are actually indexed correctly during install, an L~jet will be slightly more difficult to start and have rougher idle in general when converting to non~vvt cams with a hotter grind.
Same as an L~jet that goes all lumpy when the vvt is activated while the engine is idling.

One cannot expect the idle bypass settings to be the same from what amounts to a timing retarded very mild cam to a longer duration higher lift cam.

As to the over~rich aspect, if again you're counting just idle enrichment, you need to fiddle the bypass on the AFM itself while using a sniffer tester as the ECU does not alter the A/F ratio when the TPS is is in the idle position. It simply reverts to a pre~programmed map and the vacuum of the engine deflecting the vane moves the appropriate amount of air to work with that map. Working the ECU air bypas dials that amount of air.

If you mean rich while actually driving, then I concur with what has been said already: O2 sensor
There have been no changes significant enough to get things outside the parameters of what the stock L~jet is capable of.


@ Rich:

When fiddling the vane spring in the ECU toward lean, you don't want to move it so far that the tip of the potentiometer in the carbon tracing gets too rock steady/solid/non~moving while at idle.
It's important that it have just a small amount of float, like around 1/4" so that as things change due to harmonics and whatnot, the vane can compensate efficiently and it won't flatten out or get all surge~y.

That in turn should get you fairly close on overall mixture, or at least close enough to where the ECU can compensate as O2 sesnor readings come in.
 

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Thanks, Darren. I'll go verify. I was thinking that the PO had adjusted it because (1) the plastic cap on the AFM was not sealed, and (2) there was a light scratch on the wheel at the notch that I set it to, as if the PO had marked the original position.
 
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