z31 running lean, really lean

[generalz31]

Hi guys I have a 85 300zx turbo automatic with basic cold air intkae and a 3inch cat back
The car only has 70k on it and my spark plugs are white. I've changed them and I got the same results,white. when I first start it it sounds like a big v8 with cams, it lobes and stumblles and if I give it gas it will backfire through the intake. Once it gets to closed loop it runs fine just lean. So far I've changed the chts and the harness, iac, and the maf and haven't gotten anywhere. I've double checked the timing belt and the dizzy I'm at my wits end and I don't want to melt a psiton

[Rognine]

You said that you've checked the dizzy, but have you checked the timing itself? Also, I'd check fuel pump/regulator. And sorry for another also, but did you check the chts harness visually, or did you check for resistance across it?

Thanks

Ryan

[generalz31]

I used a timing light for the dizzy and the chts and harness are new I visually checked those

[generalz31]

Sorry what I mean is I checked the timing itself with a light, I'm wondering if my aftermarket intake would lean the plugs out its one of those big specte filters from kragen

[Rognine]

The only other things I could think of would be a vacuum leak, or a faulty O2 sensor. Sorry, I'm not really familiar with the Z31.

[Perrenial Badass]

Backfiring through the intake sounds like a timing issue to me. How did you inspect the timing belt? Did you recently change it or has it been on the car for a while and you took the covers off to check? Have you run codes? Changed the fuel filter? Checked fuel pressure at priming and while running? O2 should show a code, and if the pump is weak, filter clogged, or the ECU faulty it will either not prime up properly or run insufficient pressure while the car is running.

[generalz31]

I changed the belt , noticed the intake backfire, btw its onlt when I give it some gas during warm up, I thought maybe I had messed up somehow so I tore it all back down and double checked and it was all good... the computer was throwing a bunch of codes, if I recall they were fuel temp sensor, crank angle, chts, and vss. When I unplug the fuel temp nothing changes same goes for the aac valve connector where the idle screw is. I've ordered a new o2 sensor ill give the car a shakedown after I put that on, and the fuel filter is new.

[evildky]

a bad O2 sensor causes a rich condition, yes an aftermarket air filter will lean the car out a bit but not enough to be a problem as the stock tune is actually quite rich, this whole backfire thing is the main issue, there is a physical timing issue/valve sticking, an ignition timing issue or you are dumping excessive amounts of fuel, if the problem started after you did the timing belt that strongly suggests the timing belt got off

[generalz31]

I don't want to be the "yeah but" type of guy, when I changed the t belt I aslo changed the iac valve, the car idles fine for ten seconds or so then goes into the rough idle buisness I'm wondering if I messed up the aac when I changed the iac. I've double and triple checked the belt timing and the base timing. I'm kind of starting to think I messed up the aac or lost a part in it.

[evildky]

well if the problem appeared after the work you performed it's a safe assumption that somethign you did in the course of the work caused the issue

did you remove the plug wired or move the distributor at all in the process? getting a couple of plug wires swapped or getting the ignition timing off would expain the issues

problems with the aac or aicv would generally cause high idle or occaisionally low idle, or even off throttle air starvation, you didn't mention idle issues so we'll have to assume they are not the source fo the problems

to be clear, have you checked for codes since oyu "fixed" the othre issues? if there si a code present then there is likely a reason for each

[Perrenial Badass]

Dec 10th I had the PS cam one tooth off on my car. Idled smoothly but low, had no power, backfired through the intake. As for your codes, the CAS can cause serious running issues. The FTS and CHTS can cause some idle issues when the car is cold, or during a hot restart. None of them have caused a backfire through the intake in my experience.

Simply put, even if you do have a faulty o2 sensor causing the car to run pig rich, something else is wrong. There's an intake valve open during compression or ignition. You've got a cam off or the distributor off.

[generalz31]

Ok ill reset the dizzy, thanks for the advice, fyi when I unplug the fts when cold their is no change in idle

[generalz31]

Ok I reset the distributor and it ran great for about a minute or two then it went back into rough idle the fts is only reading 3v and it won't start while hot at all... I mean it'll start but it'll run super bad. On the plus side I pulled a plug and it was tan not white

[generalz31]

Ok I reset the distributor and it ran great for about a minute or two then it went back into rough idle the fts is only reading 3v and it won't start while hot at all... I mean it'll start but it'll run super bad. On the plus side I pulled a plug and it was tan not white

[evildky]

the cts tells the ecu that it's cold otu and to dump more fuel, when the cts si disconnected the ecu assumes it's cold and faults to extra fuel, so it won't make a difference at cold start, only once warm will ti be a problem

the fts also faults to extra fuel