Ruff Idle ,Huge Loss of Power

[ZR2]

I have been reading / watching this thread with interest. Not trying to hijack it as I have a similar problem that has just emerged. Bought a 94 ZR1 awhile back and was stored for awhile, so I was doing maintenance, oil, plugs, filter etc. and after changing plugs noticed a stumble at low rpm's. Below 2000 was where it was happening. Car had NGK TR5IX plugs in it when I got it and I put in NGK BKR5EIX plugs and after about 50 to 100 miles the stumble started. It did not have a stumble with the original plugs, so I changed out the plugs this morning, they were a light gray to slightly white in color already, so I switched to a set of AC 41-800 plugs. I just came back from a short ride and the stumble is worse. I checked the fuel pressure on the engine and prior to starting it is basically 53lbs. I have waited awhile and it seems the pressure is holding, so I think the FPR is OK, I haven't changed the fuel filter yet and know I need to. Is it the heat range of the plugs possibly or probably a somewhat clogged fuel filter? Filter looks like a pain to change.

[XfireZ51]

ZR2,

So ur saying the motor had a ?stumble? or miss at idle w original plugs, then developed a stumble with the EIX and AC plugs? Is that on acceleration, or just cruise? The 405hp motors I believe were supposed to be gapped at .050? while the 90-92 were .035?. The 5 heat range may also be a bit hot especially if u r first sorting the motor out.
Need some more detail on the issue.

[Macroblock]

To check plug wires:

Method 1 is to use an inline spark plug tester. Test one lead at a time. Connect one end to the incoming HI-Tension lead, the other to GND (normally the other lead goes to the spark plug but this is likely not possible on the LT5 due to the deep plug shaft). The tester will light when high voltage comes down the wire as you turn the engine over. Available anywhere including Amazon. 2 testers cost under 25 dollars.

Method 2 involves removing one lead at a time and gently inserting a screwdriver completely into the boot of the HI-Tension lead (don't damage the connector). Place the driver over the plenum with about 1/4 - 1/8" of gap between the plenum and the metal part of the screw driver. Upon cranking, you should see a spark jump from the tool to the plenum.


BTW - Before buying any parts, this should have been your very first test. Let us know your results.

[Macroblock]

Originally Posted by Tripler

https://www.youtube.com/watch?v=fEXF...ature=youtu.be


When the tac reaches 2500/2700 rpm the engine surges to 3000

https://www.youtube.com/watch?v=io-9ucGfg4I

Hmmm.....One cylinder could be off line due to fuel starvation. It could be an ECM issue since you've already changed the injectors.

After ruling out your ignition system by checking the HI-Tension leads, you might need to pull the plenum (again) and check your primary injector leads. Learn where cylinder 6 is.

Also - check out this thread:

https://www.zr1.net/forum/showthread.php?t=31783&page=1

[ZR2]

Macroblock, I am a different car and issue from the original thread starter. With the original plugs it did not have a stumble. I was updateing everything just doing my maintenance and when I replaced the plugs the 1st time with the NGK BKR5EIX plugs after about 50 to 100 miles I would say the car developed a low speed / low rpm stumble. Mainly at low rpms 1000 to 2000 maybe. nothing at higher rpms. Today I took out the plugs, yes #8 also, what a pain, and replaced them with some AC Delco 41-800 platinum plugs and sure enough the stumble was still there, but actually worse. I checked the fuel pressure after reading this current thread and it was at about 53 lbs with the rail pressurized but not started. It held to 30 lbs ish after 30 minutes or so. Car idles fine, just when a bit of load is put on it below 2000 it stumbles. I think the heat range of the NGK plugs was probably too hot by 1 or 2 ranges, but I think something else is going on. Car doesn't seem to be missing in the traditional way.

[ZR2]

Stumble is on acceleration not cruise. If I were cruising the car is fine, just under load.

[Macroblock]

Originally Posted by ZR2

Macroblock, I am a different car and issue from the original thread starter. With the original plugs it did not have a stumble. I was updateing everything just doing my maintenance and when I replaced the plugs the 1st time with the NGK BKR5EIX plugs after about 50 to 100 miles I would say the car developed a low speed / low rpm stumble. Mainly at low rpms 1000 to 2000 maybe. nothing at higher rpms. Today I took out the plugs, yes #8 also, what a pain, and replaced them with some AC Delco 41-800 platinum plugs and sure enough the stumble was still there, but actually worse. I checked the fuel pressure after reading this current thread and it was at about 53 lbs with the rail pressurized but not started. It held to 30 lbs ish after 30 minutes or so. Car idles fine, just when a bit of load is put on it below 2000 it stumbles. I think the heat range of the NGK plugs was probably too hot by 1 or 2 ranges, but I think something else is going on. Car doesn't seem to be missing in the traditional way.

Sounds like a cylinder or two are off-line. Any fault codes?

Verfiy the ignition leads as detailed in this thread. Afterwards, you will need to verify your injectors and/or the (-) feed to the injectors from the ECM.

[Tripler]

Thanks for the info guys . Yes , bad mechanic here . I had concerns doing a sparkplug screwdriver test might fry something so I never attempted that one
.
Thanks

Sent from my SM-A205W using Tapatalk

[lfalzarano]

You should encounter a stumble attempting full throttle at the lower RPMS you describe.

When these parameters are met: Coolant and Oil Temperature is 68F or above and System voltage is 10V or above Power Key on, and NO SES Codes, the ECM will signal the ports to open and wait for .5 second before turning on the secondary injectors at specific throttle vs, RPM. As the secondary injectors share the same drivers as that of the primaries, the pulse width signals are halved when the secondaries operate.
As shown in the diagrams (below), there are three different styles of driving which will operate the port throttles:
1. Ref. line A-B. Constant throttle position with a rising rpm. At the point the arrow crosses into the 'Port Throttle Opening Region' (top left shaded area) the port throttles open and the secondary injectors start firing.
2. Ref. line C-D. Constant rpm with increasing throttle position - logic as above.
3. Combination of the above: i.e. increasing throttle and rpm - logic as above.

The TXT attached file has the graphs of Throttle Position vs. RPM

My 90 stumbles slightly when I put my foot to the floor below 2000. Hope this helps.

[XfireZ51]

Lou,

Stock cal has a delay of .3sec.