Can colder plugs cause bad running?

[EZ-E]

Finally gotten my 82 zx turbo straightened out and it runs ok now. Things I noticed that are different before and after the fuel rail. The AF gauge goes almost to lean then back up again when I give it throttle. Never did that before once warmed up it would usually stay in the green(rich) till cruising, then jump around in the stoich.

 

I also notice at idle what seems to be like a miss. Only after sitting for a minute though. Rev the gas and its gone. Street dirving is different as well. Not as smoothe as it used to be.

 

I figured the only other thing that I changed that was different then the rail were the plugs, BPR7ES 11's. Could they be the cause of all my bad running?

[Guest bastaad525]

I wouldn't think just going one step colder would cause noticeably worse running, but it's possible. Problem with going colder is the colder you go, the harder the plugs have cleaning themselves off at low engine speeds, especially at idle.... they'll tend to load up easier. Again, I've never had this problem with just one step colder plugs, but maybe something else is contributing? What did you gap your plugs at?

 

It would be helpful to know what fuel pressure you are running at... did you install a gauge with the new rail? Also, when you say it's going lean when you rev it, is that in neutral or under load?

[EZ-E]

I gapped the plugs at .038, Currently I am running the car at stock pressure of 37 (not running) gauge on fuel rail, right at 30 like it should be during idle as per service manual (not FSM). It goes lean under load. Not sitting or at nuetral and revving.

[Guest bastaad525]

I mentioned this in onephatz's post as well. You may want to somehow check what your fuel pressure is doing under load and as boost comes on.

 

The only way I can think to do this w/o going to a dyno is to lift the rear of the car, put it in gear and start revving it with the E-brake on... but of course this will be very abusive of your brakes! Though it doesn't seem very common, fuel pressure regulators can get stuck and then of course you will run lean under load. Another thing you might try is just banging on the FPR a little rapping on it with a wrench or something sometimes that shakes them loose. Otherwise I dunno... might be something electrical... try disconnecting your ECU and sensors, and AFM... cleaning all the connections with electrical parts cleaner or as some recommend brake parts cleaner, then coating everything with dielectric grease to help prevent corrosion and keep the connections clean. I've had funky running issues when my AFM connectors or ECU connectors have gotten corroded.

[EZ-E]

I have done that already, it was one of the first things I did to the car long ago and its still everywhere. I cleaned all the grounds, cleaned and or replaced all the connectors, used quality dialetric grease everywhere, even on the relays and all.

 

Might have to try what you suggested with the car to test under load, dont like the thought of putting a fuel pressure guage in the car with me

[Guest bastaad525]

if you have the money, around $75, check it on a dyno, or if you can find some cool people, you might be able to get them to just do one pull for $30-50. This way you wont fry your rear brakes, and you'll get to see what the fuel pressure is doing all the way up to redline, as well as seeing an actual graph of your air fuel ratio. Dyno's can be just as good at helping solve problems as they can at helping to tune for more power.