Running rough/missing (94 ZR1)

[scottfab]

Originally Posted by Rusty

Haven't yet had an opportunity to check the hose to the MAP, or much else, really (landscaping projects in the yard have been taking up my time), but I did find that the following codes come up:

DTC #21: Throttle Position Sensor Circuit Voltage High.
DTC #22: Throttle Position Sensor Circuit Voltage Low.
DTC #51: EEPROM Programming Error.
DTC #53: System Voltage Low.

Will hopefully have more time on the weekend to check things out.

Great, now procedure dictates that you clear them and see what gets set again right away.

[XfireZ51]

Turn the ignition to ON, not start. Does SES BLINK once? I would check and make sure memcal was seated properly. Rough idle could indicate its running in Limp Home mode.

[Paul Workman]

Originally Posted by Rusty

I found when driving it home after purchase (~200 km) that after running for a while and warming up, the car develops what feels like a miss. It kind of makes a stuttering/gurgling/popping noise, the car jerks around a bit, and it keeps going.

This statement (in red) makes my compass point to electrical. "After it warms up"... is a classic winding kind of failure. Not saying this is your problem, but jerking and popping would go along with a cylinder or two, i.e., via the waste spark (two plugs of the same coil fire simultaneously in a loop)

But! Because you said it runs impressively at WOT, coils, wires, and plugs are set asside as culprits (for now - and you already eliminated plugs, you said). I say this because the dielectric constat (resistance to current flow) across the spark plug gap increases with increases in air/fuel mix - reaching its peak at WOT. (One reason top fuel dragsters use magnetos to throw vurtual lightning bolts at WOT!)

Relative to your symptoms, at least three important changes occur at WOT – which makes operation significantly different than normal cruising:
1) The secondary fuel pump turns on (i.e., if fuel starvation due to a failing primary pump was the problem before WOT, that problem - the stumbling at least - would be "resolved" when the secondary pump came on. Taping a fuel pressure gauge to the windshield and going for a drive will deny or confirm a fuel delivery issue: 45+ psi at cruise and about 52ish psi at WOT = not a delivery problem. I’d still change the inline fuel filter tho…



2) The secondary injectors come on so a marginal to failing primary injector would get some help from another injector coming to the rescue - to the point of possibly masking the symptoms at least, if not loss of power. Fuel starvation in a single cylinder is serious – leading to burned valves, for example. And, unlike your daddy’s 86, pulling the heads on the LT5 is a major operation involving pulling the entire engine and re-timing the cams, etc, etc. I’d wanna eliminate fuel delivery first, before putting any more miles on ‘er.
3) Didn't you mention TPS, and ECM errors? With those kind of miles, the contact point between the wiper and the rheostat inside the TPS could by now be carbon etched or pitted. This would lead to an erratic "off-on" voltage signal to the ECM which would really confuse it. However, at WOT the contact point between the wiper and the rheostat is in a "clean" place where the wiper doesn't normally hang out constantly, so the signal is steady and the ECM is not getting mixed messages.

Yeah, "more potatoes for the stew pot"… The FSM will help a lot - at least up to the point of requiring a Tech-I to manipulate something. IMO, the danger with these "I had that problem and I did this to fix it" threads is some start changing parts till the problem goes away (aka "shotgunning"), in place of methodical troubleshooting. I don't get the feeling you are that type. Whe asking for ideas, I take these scattered tidbits as reference "bookmarks" to be considered in due course rather than indication of stuff to change out.

One premier exception to "shotgunning" might be the OEM injectors - especially in a 90-92 which were affected by alcohol in the fuel. But, even a 93-95 at 140k miles and 17+ years, they can have issues. Yeah, I'd want to eliminate the other stuff first, but keep changing them in the mix.

BTW!! Welcome to the BROTHERHOOD OF THE BEAST! This issue of yours should be realtively simple to fix (if not simple to find). After you get this item fixed, I have a feeling your dad is gonna want to "test drive" your Z a lot, just to make sure it is running OK.

P.