Ok so the Z has been down for most of the year due to another bad fuel injector. Had to wait for JECS to fix it because it's under warranty and they just so happen don't make that particular one anymore. (Just my luck)

So the issue this time, which it had before it went down, is it misfires/hesitates while I barely have the accelerator pressed. Mainly on level ground or going downhill. It gets worse as the engine heats up. If I give it enough throttle to start increasing speed or even up to wide open it acts just fine. Or even if I let off the accelerator it acts fine. Just start bucking on me when I'm trying to stay at a steady speed on level ground or downhill.

Any ideas? I've google searched it with no luck.

Those who don't know my car:
1990 TT swap 2+2
615cc injectors
Z1 ECU
Z1 Dual Intake
Running 12 psi.
Aeromotive 340lph fuel pump


P.S.
Sorry I haven't been on in a few months helping with any questions. Wrecked my bike back in May and was laid up all summer.

 

I need to order a Fuel pressure regulator. Think your getting too much fuel acts like a carbureted engine that's overloading. You REV the excess fuel out and runs ok on wide open thot. Just a hunch but I think the spring inside the REG gets weak after time age getting hot and cold over the years and lets too much fuel get by. The up down hill thing is just BOGGING I woulkd think. Mine is doing the same thing, thought I had an injector problem at 1st, removed my vac to reg and cut off elbow and ran a woodscrew down, put some pressure on the diaphragm of the reg. It ran much better but effected my return some and fuel pump was singing, so I know I need a reg.

 

I see you have a different aftermarket fuel setup. is your pressure reg adjustable? May be out of adjustment. Now I,m think that you have a pressure reg with a gauge. May have a lean issue LOL. 12psi seems low but you do have larger injectors. I would try raising and lowing pressure to see if you get any effect from that. Wanted to ask does it act like it falls on its face then takes off? Hard to tell without knowing what setup you have, some have problems with return setup, air gets trapped may have to rethink that arrangement.

 

Sorry, 12 psi boost. Only things that are upgraded is the fuel pump and injectors.

It doesn't fall on its face when I accelerate. It stutters while at one steady speed on level ground or going downhill. If I give it more throttle it straightens up immediately. Acts as if I'm letting off the throttle and then pressing throttle again repeatedly (when I'm not) until I either let off or accelerate.

It gets annoying speeding up and then letting off just to keep it from doing it.

 

I have been into the z31 haven't looked into the z32's, does that engine have that idle speed control valve with the 2 solenoids like the 31? maybe the ECU is regulating then too often. Is you EGR clean? And do you have a vac running to your fuel pressure reg?

 

All vac lines are hooked up I get full vacuum and boost plus do not here any leaks. Also have sprayed lines and seals for leaks.

Don't have egr. Deleted that.

The z32's do have the big iac and all that mess. Don't know if it's the same as the z31's as I have never messed with them.

I have extra coil packs and have swapped 4 so far (1 at a time) with no luck yet. Will be trying the last 2 tomorrow.

I am almost certain it's electrical due to it gets worse as the engine gets warmer. Also worse when outside temp is warmer. Since it's gotten cold it's taking longer to start doing it. I could be wrong though.

Anyone think it could be the CAS? It has new Fuel Injectors, Spark Plugs, Turbos, PTU and ECU. I can't think of anything else if it's not the other 2 coil packs.

 

You said that you have new plugs, I would pull them and recheck the gaps. Not only that some plugs just don't work well in some engines no matter the cost. Some hot some cold. Something maybe expanding during warm up that effects your performance like the gap. You didn't say anything about codes so I am thinking of what the ECU wouldn't pick up as a fault. I guess you changed the fuel filter as well.

 

Fuel filter has about 5k miles. Plugs have the same. I have pulled them and checked the gap. They are the ones that z1 sells for the TT. That's the ones everybody says to use.

 

So I've done some testing around and cleaning connectors.

My CAS and Coolant Temp Sensor (ECU) terminals were heavily corroded. Cleaned those. Also notice the PTU spider web of a harness was loose on one connection. Fixed all these and the idle seems much smoother than it was already, but the issue I was originally trying to fix was still there.

So I sit there with it idling and letting the wheels turn in my head. I decided to see if I can replicate the issue while in neutral. I press the accelerator just enough to barely crack the throttle and the RPMs drop 100-200 and then goes back up. Light bulb flickers in my head. I test the TPS and it is open circuit when I do an ohm test on all three prongs any 2 combo while opening the throttle.

Since I know I now have a bad TPS and that it can cause the issue I'm having that will be what I replace. I also disconnected the TPS and had no change while running or driving.

Will post what happens after I replace it.

 

Ok so I finally ordered and got my TPS. Replaced and adjusted it and it solved the RPMs dropping then going up when I press the accelerator, but all my other problems were still there.

So I decided the only thing that left that could do this is something on the IACV assembly. I pulled the balance tube off and was looking at all the connectors. Had some minor corrosion and I cleaned it off. That's when I seen a broken wire on the VTC connector.

Spliced the wire back together and hooked everything back up and PRAISE THE LORD it's fixed!!!!
No more jerking while only cruising and no more stalling when I come to a stop.

Time to start on the body work.

 

Woohoo!