PanShovelMike

Hello people. Quick introduction - I'm Mike from Texas.

A little background on Vera (thats her name)... I've had this 87 z31 2+2 for about 17 yrs. She was my first car and I love her to death, but I'm ashamed to say I let a technical issue get between us for the last couple years.

This car started life as a N/A, but I did a turbo swap on it 10+ years ago. I'd been collecting turbo parts for years in preparation, so when the NA engine was tired I was ready for the swap. I dropped in an 80k mile engine from a wrecked 86 turbo. I'm running my stock N/A harness, and matching year airflow meter, ecu, and 02 sensor (can't remember if they were 84/85/86, but I know they're from the same year). The car ran great as a turbo for many years. Engine mods/specs as follows in case any of this is relevant... 240sx throttlebody (coolant passage bypassed), large k&n filter, stock t3 turbo @ 7lbs, open downpipe.

One day a few yrs ago I was on my way home from work and all of a sudden it started acting like it wanted to die on me. Engine was stumbling badly, as if it were running out of fuel. Had to feather the throttle but was able to limp it home by keeping the rpms high. If I released gas it would die. It would restart, but acting the same. I tried back then for a week or two to figure it out but couldnt. I had other cars/bikes to drive and lots of other things on my plate so the car took the back burner. Recently I've been missing her and wanting to figure this out so she can be a daily driver again.

I've been messing with it the last few weeks and I've noticed a pattern in it's issues. The car starts right up, no problem. It idles great, and throttle response is crisp. It will happily idle all day in the driveway if I don't try to drive it. When I do drive it, it drives perfectly for approx 5 mins. Then, it starts acting like it did before... runs rough, will die if im not feathering throttle, acts like it's starving for fuel. If I feather the throttle until I get it above approx 3k rpm, I can limp it home but it sounds bad and pops/backfires. Car stays this way until allowed to cool completely. Once cool, the car goes back to being happy and stays that way until the next time I try to drive it.

The car has fresh fuel, new cap/rotor, new plugs and plug wires. I've checked/cleaned all injector plugs, tps plug, airflow meter plug, 02 sensor plug, chts plug, and ecu plugs. The autometer boost gauge reads approx 20 vac at idle which was always normal for this car.

I did search through this forum and others before posting but didn't find anyone with the same issue. Can anyone point me in the right direction here? I have not checked fuel pressure yet to see if it fluctuates when the car is acting up (don't have a gauge). Anyway... any input or ideas greatly appreciated and I'd be glad to answer any questions or perform any tests to help diagnose this... I just need a little help as it's not like it used to be when I was a kid and could spend all my waking hours figuring out car problems and I can't afford to just throw money at the problem. Thanks for your time and I look forward to hearing back.

zxguy1986

Welcome to ZDriver

Solid, clear post, Mike from Texas. Well done. Others here are better at swapped turbos and their issues than I am.

The prob could have a number of causes. It sounds to me like the trouble I had when the solenoids on my air regulator went on my '86NA. Intermittent stalling out, feathering, etc. Not familiar with the air reg set up on your motor. Definitely sounds temperature related to me. Stick around for other input.

mtherkamp

Sounds like it may be a problem when the car goes into closed loop control. Give us some more details on your build, egr, air, aav, idle controls? Let us know if you have any deletes. Any of those things as well as CHTS or O2 sensor could cause what sounds like a lean condition to me.