GTZ _STILL_ running rough

[DanteGTZ]

As some of you know I've been battling a miss and lack of power for a while in my Quad4 Quasar GTZ. I am really at a loss now as I would like to take this car to Bfest. The engine is brand new (~800 miles), timing is good, compression is within a few PSI between each cylinder (cold). I have replaced every single sensor (one by one), swapped coils, ignition module, ECM, memcal, etc.

The tough part is I bought the car without an engine and therefore have never seen the car run properly. I have checked all wires, replaced the injectors, injector harness, alternator, battery, everything I can think of.

Anyone else run into a situation like this??

[SuzukiGhostRider]

What about the fuel pump? Also what are your compression numbers?

[woody90gtz]

Ummmmm. OEM tune I assume, so it shouldn't be tune related. Seems like it would have to be somewhere in the harness?

[1988GTU]

Make sure all factory grounds are in place.

[SuperLbody]

Definitely check the fuel pressure and not just at idle or looking for pressure only, unplug the vacuum from the regulator and make it go to max fuel pressure. That way you can see if the fuel pump is able to deliver the fuel needed.

[Asylum]

I have a '91 Quad ECU you can have for free that I know is just fine.

Just pm your address.

Not perfect, but might give you something to compare to.

BUT WAIT A MINUTE!

You have a couple of these things that run just fine, RIGHT?

You have swapped some stuff to see?

It's got to be a bad or missed ground, or something equally as silly.

That said, the travelling hoard is about to descend on your home in the next few weeks and one of them will figure the damn thing out.

[ifixalot]

On my 96, z26, v6, It would run fine cold, then after 3-4 minutes, I could give it a little accelerator
and it would shudder and actually drop rpm unless I gave it more accelerator.
It turned out to be a bad spark knock sensor. I heard they get sensitive and retard the timing
when it doesn't need to be. As a test, I unplugged it and the car ran much better.
So then I replaced it with a new one and the car has been fine ever since.
But before I found this I replaced every damn thing, MAF, TPS, MAP, FP reg, ICM, wires, plugs,
ATS, CTS, oxygen sensor and the ECM.

[SuperLbody]

Could you get a scan tool and monitor the data feed?

[3X00-Modified]

We did that in TN and nothing stuck out as wrong or not reading correctly.

[DanteGTZ]

I'd like to try and verify my fuel pressure - My 93 fuel rail does not have the schrader valve on it like the earlier Quads do. Has anyone built an adapter that would snap in line of the factory fuel line (the one that attaches to the driver side strut tower)? I'd rather not have to cut/splice something into my factory hoses/lines.

Any thoughts on this?
http://www.nitrousoutlet.com/nitrous-ou ... apter.html

Looks like it'd be exactly what I'm looking for. I'm open to suggestion for ideas.

[SuperLbody]

Well let's narrow it down a bit. When you say a miss and lack of power where does it occur? Is it in a range or wide spread? Does it happen more warm or cold?

[Rettax3]

I had made a snap-in adapter line at one point (several different ones, actually), but they were all stolen a few years ago with my other diagnostic tools. If you can find a donor out in the junk-yards, it is easy to make something that works. Personally, I think it is stupid not to have a test-port, so on my '97 Z-24 (2.4 Twin Cam), I cut the metal line near the cam housing and installed a Tee fitting (heavy-duty compression fittings for industrial applications -spend the extra money on some quality parts), and put a brass Schrader valve on it -I could check my car's fuel pressure with a tire-gauge if I couldn't (for some inconceivable reason) put the correct gauge on it. I later just installed a permanent gauge from an adjustable FPR.

I replaced a dead pump in my '90 Turbo 'Retta a short time ago, and the new pump was defective. It supplies pressure just fine and would pass all of the tests normally expected of it in a bay, but once actually driving, you can see that under load the pump cannot deliver the volume necessary to keep the engine running properly and the pressure drops out. However you test your fuel pressure, make sure you can see the gauge while you are driving the car, and can verify proper pressure even while it is having the performance trouble. Good luck.

[DanteGTZ]

Well let's narrow it down a bit. When you say a miss and lack of power where does it occur? Is it in a range or wide spread? Does it happen more warm or cold?

It occurs all the time - Warm/Cold/LowRPM - It is basically there all the time.

[SuperLbody]

Well let's narrow it down a bit. When you say a miss and lack of power where does it occur? Is it in a range or wide spread? Does it happen more warm or cold?

It occurs all the time - Warm/Cold/LowRPM - It is basically there all the time.

Hmmmm, well fuel pump is the one we all mentioned. You mentioned coils and wires, what about the spark plugs? Possible restriction of the exhaust?

[DanteGTZ]

I'm going to have to rig up something to test my fuel pressure but I'll get to that middle of next week.

As for the other stuff, everything else has been checked. Coils, Ignition Module, Plugs, Boots, O2, TPS, IAC, Coolant Temp Sensor, Injectors, Inj Harness, Knock Sensor, CPS, etc. Literally every sensor is new and replaced separately for testing. Exhaust manifold is clear and cat temps appear normal before and after.