[CootersXR7]

Long time minor issue with my '85 I was hoping a few of you could speculate on. Pretty sure I had previously posted some 4 years ago or so, but unsure which old forum. 

Anyways, my '85 Turbo Coupe (mostly stock) has a backfire I've been trying to find for years. It's just a popping, kind of quiet, backfire I hear on deceleration. TPS has been checked, all new Motorcraft ignition stuff as well. I swapped an ignition module with same results, and all I had left to easily try was a new VAM. So, I ordered one. I tried it a couple weeks ago, and it did make the backfire go away, but ran rich as heck and then wouldn't build boost. I'm wondering now if somehow the new VAM put the car in Limp Mode, but couldn't get it to reset and ended up putting my old VAM back on. Should I try it again, or what else should I check for? Thanks for your help

[TurboRay]

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Velly eenterestink, Cooter! .Based on the results of your A-B testing..... it seems obvious (at least to me), that your backfiring issue must result from a lean mixture at "tip-in". Are the two VAMs the same size (large vs small)? The "door" on a small VAM is drawn farther open than a large VAM with the same volume of air passing thru, thus providing a different "signal" to the ECU. That's why each VAM must be paired with an ECU calibrated/programmed for its size.

If the two VAMs are the same size and since swapping 'em changes the AFR....... I would try either loosening the VAM-door tension/spring on the "old" one to signal the need for more fuel (richer AFR) ~ OR, tightening it on the "new" one to signal a need for less fuel (leaner AFR).  

If neither of those two potential "remedies" are successful, AND if you're satisfied with the driveability of your current ("old") VAM...... there's an air-bypass adjustment on the VAMs that MAY change the idle/tip-in AFR = LINK. However, if you decide to try different adjustments - whether door-spring tension or idle-air bypass - I suggest somehow marking the stock adjustments beforehand (Sharpie, whiteout pen, etc.), so you can return to the stock adjustment, if necessary. <shrug>  GOOD LUCK!

[dan_xr4]

I had some popping in the exhaust during deceleration when I had a small exhaust leak, in my exhaust manifold, on a non-turbocharged car.