85T Bad Hesitation/Hiccup/Misfire

[JLaraZ31]

So recently I've been having this problem, I've looked into and searched others with similar problems to try and find a solution. At first I thought it was the CAS because it threw that code. Upon replacement, the code went away but I still had the same problem, checked codes and founs for CHTS, ended up being the wire coming undone from the harness.
After that I also adjusted the AFM with guidance from the fuel service manual to get it to where it needs to be; I also checked for vacuum leaks but couldn't find any. It ran better but still had the issue. Replaced the sparkplugs as They were pretty fouled and looked like they needed to be replaced. Ran much better and only hesitated bery lightly but was still hesitating.

At on point it didn't want to hit boost as I went through the RPM almost as if it was in limp mode. Whenever I revved it in idle it would black smoke but I dont have any codes except for idle switch which I've had for a while causing a high idle.

I do have an intercooler as far as mods go, I'll check distributor timing tomorrow and double check for any vacuum leaks or loose connections in the couplers.

any input would greatly appreciated

[JLaraZ31]

So I went to check the distributor timing and vavuum leaks (haven't checked intercooloer set up yet)and didnt find anything wrong, took for a test drive and it still acted up. When I got back went to pull the ecu for any codes and when I went to turn the key it didn't light up. I tried another ecu that I have to see if it did the same but it wasn't getting any lights either.

if any one could help guide me in finding where the power source goes for the ecu that would be appreciated as well.

[JLaraZ31]

Was a blown fuse, got it to run again. Still having the same issue though. Will check CHTS again as well.

[JLaraZ31]

So after checking a few small things I started driving it around town and it didn't to do it as much when it was at ooerating temperatures. Sometimes it would do it but it would be for about a 1/4 mile and than be normal. After having left the store to go home it didn't do anything out of the ordinary at all except for one time when getting off on a light and the engine temp was roughly a quarter on the gauge.Any input on that?

[JLaraZ31]

Went to read to spark plugs (3 days old) and they are blacks than charcoal. I know the CHTS is good so I'm leaning towards the waiting right now. I'll check that out later today.

[JLaraZ31]

Well the CHTS wiring is good, still having that issue. Will pull the intercooler piping today and inspect to make sure everything is tight amd sealed.

[JLaraZ31]

Double checked my intercooler piping and everything was fine but still checked everything. I also double checked theAFM calibration to make sure it wasn't too rich or lean. I changed one plug wire and it almost didn't act up until I got home from the store but it wasn't as terrible as it was before. I'm going to replace the rest ou'd them and see if that fixes it. Looks like it may be the plug wires. Whenever I can I will update on it.

[FrozenZ]

If your plugs say that you are running crazy rich there's two other things worth checking, the TPS and the O2 sensor. The old school wisdom was that the O2 sensor didn't do anything outside of "cruise" but I found that when I had an otherwise perfectly running turbo motor, without the O2 sensor the car had serious driveability issues. It's probably worth replacing.

If the TPS is set wrong, or failing intermittently and giving weird readings, the fuel pump could be kicking in and out when it shouldn't.

[JLaraZ31]

If your plugs say that you are running crazy rich there's two other things worth checking, the TPS and the O2 sensor. The old school wisdom was that the O2 sensor didn't do anything outside of "cruise" but I found that when I had an otherwise perfectly running turbo motor, without the O2 sensor the car had serious driveability issues. It's probably worth replacing.

If the TPS is set wrong, or failing intermittently and giving weird readings, the fuel pump could be kicking in and out when it shouldn't.

I'll double check the TPS again as well as the O2 sensor. But wouldn't the O2 sensor not allow me to check AFM calibration in that setting if it was bad? Just curious as i am still learning about the z31.

[NissanXRMA]

How old if your dizzy cap and rotor? Are they OEM?

[JLaraZ31]

How old if your dizzy cap and rotor? Are they OEM?

No, the PO replaced them a few months before I bought it as well as the CAS. I'm also using the PRW2 Power transistor and have recently replaced the ignition coil a month ago.

[FrozenZ]

I'll double check the TPS again as well as the O2 sensor. But wouldn't the O2 sensor not allow me to check AFM calibration in that setting if it was bad? Just curious as i am still learning about the z31.

Only time I ever calibrated my AFR was with a brand new O2 sensor so I can't say what happens if you try it with a funky one. The ECCS will happily accept non-sane inputs like -50C fuel temps and try to work with them, so I'm not sure how far I trust its diagnostics.

[JLaraZ31]

Only time I ever calibrated my AFR was with a brand new O2 sensor so I can't say what happens if you try it with a funky one. The ECCS will happily accept non-sane inputs like -50C fuel temps and try to work with them, so I'm not sure how far I trust its diagnostics.

Hmm good to know. I'll look into my O2 whenever i have the chance.

also, while I'm waiting to get my plug wires i bandaged mine with electric tape and have only had a slight stutter on cold start after 2nd gear.

[JLaraZ31]

Update: I got installed new plug wires and it only hesitates at cold start for 2 gears. I'm wondering if maybe I didn't properly install one of them fully (cylinder 4 was the hardest for me) but after that it doesn't come back anymore. Thoughts?

[Z_Karma]

Also could be ECU related.
My 84T runs fantastic, no problems, passes emissions and is reliable.

However, if i try to drive off on a cold start without letting it idle for a minute or so, it'll buck and stutter and maybe backfire if i don't let off or feather the pedal.
The earlier ECU's had a problem with lean surge when they're cold. IIRC, there was a known issue and a second module was added into the harness and mounted
beneath the battery tray, although i cannot find the TSB that mentions this. Mine has this module and still has issues with cold starts.

There was also an oldschool fix by switching the CHTS signal to the FTS

Some info is still archived in various forum threads like this but a lot is not easy to find anymore.

Over the years on here and other forums, I've pretty much surmised that the best remedy for this cold start/lean surge issue is to convert what is required to run a later model ECU.

This may or may not be related to what issues you are encountering but it could be related.