3000 RPM Misfire

[peterpilot9]

Hi,

New to the forum but have owned my Z since 2000.

My car is a 1990 300zx na automatic. I have recently completed an injector replacement, complete with a plenum pull but no coolant by pass.

Before the injector replacement, I had the following symptoms;

1. Rough idle
2. Hesitation on acceleration
3. Check engine light, but I did not know the codes

After the injector replacement, the engine idles very smoothly at a consistent RPM, pulls off idle with no hesitation, doesn't overheat and makes no strange noises or smells

However, it has a new problem. It will accelerate cleanly, under part or full throttle, up to about 3000 RPM. At that point it acts as if I have installed the world's worse rev limiter. It cuts out, misfires, spits and bucks like it wants to give up the ghost.

I have learned to read the codes, and I have the following; 32, 33, 34 and 51. Now, I have no idea which are new and which were there before I did the work.

So, does anyone have an idea about this issue? Starts fine, idles fine, runs fine until you hit 3000. Perhaps the 34 is related to the detonation sensor? I have read that the ECU retards timing if detonation is sensed. Maybe the 51 indicates a problem with an injector clip, but in the past that has shown up in a rough idle and constant misfire of the affected cylinder.

Thanks for any help. It would be greatly appreciated.

[nexus08]

My bet is something is throwing it into "safty mode" where because it doesn't know exactly what is going on in the engine, it runs with default values and limits the how high the engine can rev to protect itself.

Those codes relate to -
EGR Function
O2 Sensor (left side)
Knock Sensor
Injector circuit

I would start by fixing those codes. Some of them could well be just bad connections, so pull and clean the connections on them and see if the codes go away. May need to disconnect the battery to clear the codes, then run it again for awhile to see if the codes are truly gone.

http://z32.wikispaces.com/ECU+Diagnostics

[peterpilot9]

Thanks! I'm giving that a try as we type but haven't thought of doing the battery disconnect. I'll try that and see what happens. In any case, I also discovered a broken pipe aft of the resonators so I'm under the thing patching that one up. Maybe one day I'll treat her to a new set of pipes.

[peterpilot9]

Thought I'd post a quick update.

I was attempting to pull the detonator sensor's plug to give it a look, but the clips are broken and I was interrupted, so I ended up basically just tugging on the thing for a few minutes. Later, I fired it up and took it for a 20 minute drive.

No check engine light, no misfiring from idle to redline at full throttle. Unreal.

So, it would appear just playing around with the detonation sensor plug is good enough to clear a code 34 as well as a 32, 33 and 51 Perhaps the ECU remapping in a safe mode affected the other inputs. No idea, just happy to have finished a plenum pull and have a clean dash, a smooth idle and no miss at red line!

Of course, tomorrow is another day......

Thanks for the help and here's a link to a page that describes the ECU safety modes.

http://z32.wikispaces.com/Safety+Mode

[nissanfreak12]

Or just moving the wires around gave it a better connection from an old 20 yr harness. Check the connectors, you my have green crud in them, just clean them and you should be good for now until the harness finally goes.

[nexus08]

Good news. Congrats!