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Weird fluctuation in RPM

AIbandit

AIbandit

NAXJA Forum User
NAXJA Member
Location
Chico, CA
Anyone know what would cause this fluctuation in RPM? I had the pedal down the whole time but it was fluctuating on its own.
mostly heard up until 15 seconds or so then again at the end.
Renix stroker 99+ intake/TB
 
Last edited:
Got a race coming up, really could use some help.
4.6 renix 99+ intake/TB
Aw4
Atlas
 
The renix guys will know better on this for engine causes.

Could it be the transmission? That's a lot of power pouring though. Torque converter lock and unlocking incorrectly ?
TPS and transmission computer ?

Long time ago had a car with a screwy fluctuating rpm. Turned out the aluminium intake manifold warped.
I'd double check the intake and TB are not leaking. Doubt it. But wouldn't hurt to make sure.


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I thought it might be the torque converter too but someone more experienced than I said it wasn't likely.

I checked for vacuum leaks. Going to run through the sensors. It cuts out a bit while rolling on the throttle while below running temp, it goes away at WOT.
 
I Maybe over thinking it. If the transmission is ok then is the fuel supply?
Used to hang with some guys who upgraded their turbos then had upgrade the mass air and injector to avoid fuel cutoffs in the oem computer.


Sent from my iPhone using Tapatalk
 
Hopefully it's not fuel delivery, I am still running the renix fuel system with 19lbs injectors. If it is fuel delivery I'd probably have to go to a higher pressure setup.

I'd think that it would just drop in RPM steadily not fluctuate like that. Maybe a symptom of the pump taking a crap? Anyway I'll see about checking pressure while I'm at it.
 
I can't seem to get the video to load, another Naxja glitch? I can run them in other tabs but I need the url for the video.

Rattling-loose catalyst? O2 sensor or wires going bad. Bad TPS sensor? I agree, check the fuel pressure while running!!! Is it using the vacuum operated fuel pressure regulator for Renix fuel rails?
 
Ecomike said:
I can't seem to get the video to load, another Naxja glitch? I can run them in other tabs but I need the url for the video.

Rattling-loose catalyst? O2 sensor or wires going bad. Bad TPS sensor? I agree, check the fuel pressure while running!!! Is it using the vacuum operated fuel pressure regulator for Renix fuel rails?
Click to expand...

I tested the TPS when I mounted it on the 99+ intake.
Yeah it's using the oem renix regulator.
 
You have been running this stroker of yours how long before your rpm issue began to fluctuate? I have come to understand that the TPS can be mis-handled, can't remember 'fer 'sho. Beyond that, not having a more concentrated sub forum for RENIX, and your build seems to be somewhat mismatched, I will add; http://www.cherokeeforum.com/f2/iac-tps-cpk-map-failure-symptoms-each-160770/ Your TPS is probably ok given the horrible symptoms it can wreak. However there are other issues, frayed wires, bad grounds, etc. I doubt you have those issues as you have built up a racing rig, and have probably put a bit of professionalism into your quality work. Never the less, I'd go through and double check.

Did you wing it, or faithfully follow; http://www.naxja.org/forum/showthread.php?t=1072534

BTW: Another type possible upgrade for your racing adventures; http://go.jeep-xj.info/HowtoTBspacer.htm Good Luck in all regards.

I used to race my 356B on Hwy 1 from Bodega Bay to Fort Ross, and back with various buddies some 46 years ago. From Santa Rosa to Orville, and back too. What kind of racing are you doing with your heep?
 
Do you still have the ballast resistor in it?

Sounds like fuel, maybe best to check out the obvious first. Voltage and ground to/at the fuel pump.

A lot can go wrong in the fuel pump power supply circuit. Half a dozen connectors to corrode or do a slow meltdown.

Voltage isn't the whole story either, amps count also. Connector corrosion can be insidious.

I've hooked up a fuel pressure gauge and tapped it to the windshield wiper so I could watch it while I'm driving.

WOT bypasses the ballast resistor and parts of the normal path for the fuel pump power supply.

Is this tech.? Am I in the right forum? Did I say anything that may get this thread poofed? :twak:
 
Plugged fuel filter? I would think the pressure would vary if that was the case.

I remember back in high school, someone brought in a vehicle that would not run very well when the throttle was pressed, but would idle just fine. It turned out to be the fuel filter.

Tom
 
8Mud said:
Do you still have the ballast resistor in it?

Sounds like fuel, maybe best to check out the obvious first. Voltage and ground to/at the fuel pump.

A lot can go wrong in the fuel pump power supply circuit. Half a dozen connectors to corrode or do a slow meltdown.

Voltage isn't the whole story either, amps count also. Connector corrosion can be insidious.

I've hooked up a fuel pressure gauge and tapped it to the windshield wiper so I could watch it while I'm driving.

WOT bypasses the ballast resistor and parts of the normal path for the fuel pump power supply.

Is this tech.? Am I in the right forum? Did I say anything that may get this thread poofed? :twak:
Click to expand...

LMAO, off to the dungeon you go, misstress Jade will explain your infarction to you the hard-tech way with a BFH, LOL.

The more I think about it, the idle fluctuation, it could be any one of dozen things in the early stage of dying.

I like the fuel gauge on the dash wiper blade solution, I take it was raining in the mud that day? LOL

It could be a loss of signal or ground just about aywhere in the fuel or spark circuits from the computer to the sensors to the injectors to spark coil.

I wonder if cruiser54 has a complete TECH list of OEM places that cause sudden RPM drops that in my world always eventually lead to no starts or sudden dying of the engine at stops or while driving. I have been too ill the last 2 years to keep up with refinements on renix fixes and diagnostics.
 
I still need an actual html link or youtube url so I can watch the video as it will not run on naxja while I ran you tube videos all dat today in the same browser. Also I can not right click to bring up the URL which I can do every where else. Very odd.
 
Green Mesa XJ said:
If you quote him the video I'd appears, should be able to past it over at YouTube.


Sent from my iPhone using Tapatalk
Click to expand...

Nope, not there either.
 
Green Mesa XJ said:
I can see it my phone. I'll try to cut n past


Bql0xTQkRh0. YouTube id

https://m.youtube.com/watch?v=Bql0xTQkRh0 direct link

It's in a forum software box so I doubt I could see it if it weren't for Tapatalk translating


Sent from my iPhone using Tapatalk
Click to expand...
Looks like he has the front brakes applied somehow and spinning the rear tires? How is that anykind of an engine speed wandering test? If that is the right video it could be the drive trane, transmission or transfer case going out, or he is hitting the fuel pump flow limit, or the brakes/road-tire slippage is coming and going. It is possible to flow test the fuel pump, but is a renix fuel pump able to push enough fuel for that modified rig at that load rate, the OEM book will not answer that question?
 
It wasn't a test of anything it was a hey I'm going to burnout on these crappy old tires... Whoa that's not normal.
 
AIbandit said:
It wasn't a test of anything it was a hey I'm going to burnout on these crappy old tires... Whoa that's not normal.
Click to expand...

Almost forgot, the fuel hose on the fuel pump in the tank may be coming loose, and leaking.
 
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