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Discussion Starter #1
Actually I\'m running too rich at WOT

Here's the story. I had my cam gears tuned on a dyno and all went real well, car ran awsome. Two day's later I'm on the freeway cruising about 80 MPH and decided to open her up so I went to WOT but the engine began to stumble, not a mis-fire as in plugs breaking down or an ignition problem, but more like fuel starvation. The car otherwise runs great, normal acceleration is still great and smooth as silk as is the idle. boost comes in as usual, but when I nail it, it stumbles at WOT every time. I'm thinking a trashed up fuel sock and disk filter, or worse yet a dying fuel pump. Anyone experiencing these conditions I would like to hear from you. thanks, Dan
 

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Re: Engine stumble ... you thoughts??

My first thought.....Injectors, you probably need heavier duty. I don't know if that's it for sure, but see what other people say.
 

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Re: Engine stumble ... you thoughts??

My first thought.....Injectors, you probably need heavier duty. I don't know if that's it for sure, but see what other people say.
ditto , either that or low octane gas.
 

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Re: Engine stumble ... you thoughts??

its, definitly not the injectors, saturday at the dyno he was running very rich at fuel cut off.
 

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Discussion Starter #5
Re: Engine stumble ... you thoughts??

My first thought.....Injectors, you probably need heavier duty. I don't know if that's it for sure, but see what other people say.
ditto , either that or low octane gas.
Not either one of these problems. I'm still running on the same tank of 93 octain gas that I had at the dyno, and as far as injectors go, my car is actually running a bit rich according to the wide band at the dyno shop.
 

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Re: Engine stumble ... you thoughts??

vacume leak somwhere perhaps
Or one of the maf or fuel rail plugs not connected properly? check the plug wires and coil... try ressting the ECU?
 

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Re: Engine stumble ... you thoughts??

My car has run really rich at WOT, at Low RPM Especially, Two times.
Both were due to O2 Sensors.
WOT at Heavy Load equaled Rich and Stumbling.
 

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Discussion Starter #9
Re: Engine stumble ... you thoughts??

My car has run really rich at WOT, at Low RPM Especially, Two times.
Both were due to O2 Sensors.
WOT at Heavy Load equaled Rich and Stumbling.
I think this might be where I need to look. First off let me explain. I initially thought I was running out of fuel at WOT, but today I had a chance to take it out on the freeway during the day and open it up. The car runs great everywhere except at WOT. At WOT it stumbles and bellows out black smoke indicating a rich condition, but only at WOT. Otherwise the car runs great. It accellerates great, idles smooth, and the plugs indicate everything is good. I checked for vacuum leaks and inspected the bypass valve, all looks fine. BTW: I haven't got a CEL either. I've been running this exact setup for months now without any problems and I haven't made any changes other than having my cam gears tweaked on the dyne, ant it ran great there, so i'm thinking something has gone TU, but what ... I dunno. Anyway, I am fortunate enough to have my wifes car to swap pieces with so I think I'll do that tomorrow and see what fixes it. I'm kinda thinking it will be an 02 sensor. Wish me luck. And thanks for all the input everyone.

Erik, I'm still hitting 7lb boost as usual.

Just for your info:
JRSC
2.6" Pulley
FCTB
70mm ProFlow MAF
Cool Flow intake
Kamikaze header
Magnaflow catback
stock ECM (no chip)
stock fuel system
 

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Re: Engine stumble ... you thoughts??

Good Luck.

If youinduce the Stumble quite a few times, it will blacken the plugs if it's running rich, but they should clean up w/ some runs that aren't at complete WOT.
If they don't clean up, you may have to replace them, but it sounds MUCH like the stumble I had.
Try driving at 35 in 5th and Floor it.
If it coughs like it's out of gas until you let off a little, it's almost certainly the same thing.
The first time mine ever did that, it was the O2 sensor after the cat.
 

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Discussion Starter #11
Re: Engine stumble ... you thoughts??

Good Luck.

If youinduce the Stumble quite a few times, it will blacken the plugs if it's running rich, but they should clean up w/ some runs that aren't at complete WOT.
If they don't clean up, you may have to replace them, but it sounds MUCH like the stumble I had.
Try driving at 35 in 5th and Floor it.
If it coughs like it's out of gas until you let off a little, it's almost certainly the same thing.
The first time mine ever did that, it was the O2 sensor after the cat.
Yeah, I think your on to something. I does clear up when I back off the throttle, and the plugs clean up just fine. I'll do an 02 sensor swap with my other car tomorrow, I'm keeping my fingers crossed that this will fix the problem.

BTW Michael, do you live on your computer
Thanks man
 

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Re: Engine stumble ... you thoughts??

I had a very similar problem with my JRSC when I first installed it-stumbling only at WOT in 3rd or 4th gear. Ran great all other times. After sending my DFMM back to Jackson for testing and finding that it was OK, the problem turned out to be a bad connection at the T-tap on the mafs wires. I soldered the connection and problem solved. I'm assuming that I was running out of fuel when that happened. Don't know why a problem like this would show up all of a sudden but it might be something to look at.
 

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Discussion Starter #13
Re: Engine stumble ... you thoughts??

Just an update. I swapped both 02 sensors with the ones from Kathy's car and removed the clips from the DFMM wiring and soldered them up. Still running the same. Car runs great except for WOT which is super rich. So I have more investigating to do.
 

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Discussion Starter #14
Re: Engine stumble ... you thoughts??

The saga continues. I fixed what looked like a bad spot in a vacuum hose and checked everything else out that I could think of and the problem persists. But, this time out for a test drive I paid a little more attention to what was going on. What I discovered is interesting. The car runs great even at WOT in 1st - 3rd gear, but once at highway speeds it stumbles and runs rich. I paid attention to the RPM through this and noticed that if I feather the throttle it clears up after 4k and starts pulling like a mofo. Going through 1st through 3rd, the RPM builds up so fast that I feel a slight hiccup between 3 and 4k and then it runs great. I went back to my dyno sheet and as I said before, there is a spot where it's too rich, and sure enough, it's in the mid RPM range. So I guess nothing is broke. I just got to figure out a way of adjusting fuel in this area.
 

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Re: Engine stumble ... you thoughts??

Sorry for the mis-diagnosis, but it was worth a shot....

The symptoms mystified my local service techs, but when they changed out the O2 sensor, it fixed it...
 

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Re: Engine stumble ... you thoughts??

Dan,

I was looking into a fuel solution (pre-explosion) and was pointed towards the MAFterburner... may help.

But itmay be worth it to see what that new tuning software will do (assuming it's actually avaliable to us as soon as we think it will be)
 

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Discussion Starter #18
Re: Engine stumble ... you thoughts??

Sorry for the mis-diagnosis, but it was worth a shot....

The symptoms mystified my local service techs, but when they changed out the O2 sensor, it fixed it...
No such thing as a mis-diagnosis in this case, just some great ideas etc. Thanks to all that have replied.
 

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Re: Engine stumble ... you thoughts??

I have a DFMM box and do not know how it is supposed to be hooked up in a ZX3 with JRSC. Can you help?
 
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