BIGSLVRXJ
NAXJA Forum User
- Location
- Des Moines, Iowa
Alright ya'll, here's what I've got. 1990 XJ 4.0 AW4. I posted a while back in mod tech because I have an HO intake on an 87 motor. However I don't really think this belongs in mod tech anymore because I have pretty much figured out it has nothing to do with the HO intake. About 2 months ago I got done putting a "new to me" motor in my 90. It was a 124k mile young 4.0 from an 87. I bought the APN header thinking it would work, however it wouldn't clear my Renix intake manifold, so I used an HO intake manifold. I used the correct mixture of sensors from the Renix/HO years to make it work just fine. The problem I'm having is that in the morning when I first start it up it will idle fine for about a minute, around 700-800rpms about where an XJ should. Once it gets going for about a minute however it will drop significantly, to around 250-300rpms. I'm also having an issue with it backfiring and bucking in the morning but then it will go away for the most part and it has plenty of power. Fuel pressure is more than adequate resting at about 33psi with the regulator line on and about 42 with it off. Mechanics stethoscope(sp?) tells me all the injectors are firing just fine as well and by the way they are the Renix injectors. EVERY sensor aside from maybe the SYNC has been replaced. Throttle body is clean and so is the IAC passage. I loosened the distributor clamp and tried moving it around in the groove it was resting in, it seemed to help slightly with the backfiring but none with the idle. The idle screw on the HO throttle body has not been moved either since right now it is set how every other HO I've seen is. I'm honestly thinking about taking it to the dealer and having them hook the ignition scope up to it to check out the whole slew of things but first I figured I'd prod at you guys once more. Can anyone help?
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