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| Miss at high RPM's http://www.4g61t.org/forum/viewtopic.php?f=6&t=34231 |
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| Author: | fastasleep [ Sun Feb 06, 2011 10:19 am ] |
| Post subject: | Miss at high RPM's |
The problem I am having is on my Mirage (Ricky's old car); Dr. 2.0 and I have been working together to try to solve this problem, but my lack of available time lately has taken its toll and I would like to get this problem corrected so that I may use my time to drive instead of troubleshoot this car. The problem is a miss at high RPM's. If I am free-revving it, the miss will occur at about 5000 RPM if I quickly push the pedal down; it will miss at about 6000 RPM if I gradually run it up to the rev-limiter. If I am driving and am in boost the miss will occur at about 3800-4200 RPM. If I driving and am in boost but gradually apply pedal (get boost later in the rev-range) the miss won't occur until about 4200-4500 RPM. This problem was noticed when I was doing a re-tune (from E-85 to gasoline) at DynoProven with Ngoc and Thuoi (Dr. 2.0). I spent many hours there and they were gracious enough to charge me next to nothing. Thanks, guys! What has been done so far: 1. Two new sets of spark plugs. They have been gapped all the way down to .024, but are now at .026 (NGK BPR7ES). 2. Three sets of spark plug wires. One set was a cheapie new set, one was the original set, and one was a set of used Magnecore's. 3. Compression check is *okay*. Cylinder one is a little low, but it had the same reading when the car was making 505hp on the E-85. 4. The car has been tuned on gasoline. I have an excellent AFR (up to the miss that is, it is confused once that hits) through the rev range. 5. I am using a MAF-T and an AFC to tune. I have wideband in the car. 6. The tank is super clean, the filter is new (changed it after being at the dyno). I have a 255lph in the tank. I took it out and it pushed to >100psi (guage-limited), then the overpressure valve relieved on the pump itself. 7. The fuel does reference boost and vacuum at the Aeromotive FPR; fuel does not dive in the higher rev's. I don't think this is a fuel issue....... 8. I pulled the valve cover yesterday. The car has BC springs in it with big cams; nothing was visually broken or bent (springs and rocker arms). 9. I did find that the car was a tooth off on the exhaust side (was advanced one tooth). I reset it and the miss was STILL there although it seemed to miss a *little* higher in the rev-range. 10. I have tried 3 CAS's. Two were known good ones. One was the original one on the car. 11. I have changed coil packs. 12. I have changed ignitors. 13. I have checked for boost leaks. 14. I have changed MAF's. I had a couple of 3" MAF's on the shelf so I changed one with no success. The MAF-T has not been changed. 15. The TPS is at .9VDC at idle and is at 4.6VDC at WOT. I have a new JayRacing 342hp pump to go in it, but I don't think this is my problem. I feel that the problem is cyclic; meaning that one cylinder is dropping out on every power cycle. This would leave me to believe that the problem is cylinder-specific, like A fuel injector or A valve spring, or A spark plug........dunno. But I am pulling my hair out! Anyone have an idea? Again, thank Dr.2.0 for all of your help. I am just trying to get more ideas.......possibly someone has run into this before? -Les |
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| Author: | fastasleep [ Sun Feb 06, 2011 11:28 am ] |
| Post subject: | Re: Miss at high RPM's |
Also, I have changed ECU's. The car drove well but still had the miss. I am also having to run my 780cc injectors as 450cc injectors on the MAF-T plus enrich it with the AFC. Does this offer anything? -Les |
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| Author: | Natedog [ Sun Feb 06, 2011 12:04 pm ] |
| Post subject: | Re: Miss at high RPM's |
I've never seen one go bad, but did you try another resistor pack for the injectors? |
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| Author: | fastasleep [ Sun Feb 06, 2011 12:58 pm ] |
| Post subject: | Re: Miss at high RPM's |
I haven't either, Nate. But I have one....I might as well. Thanks for the input. I need to change the injectors. I was wondering if my 780cc injectors were actually smaller (don't know how, though)....... This would explain having to run the MAF-T as translating a 450cc injector instead of a 780cc injector to get the AFR that I want. AND running an injector at an increased duty cycle would heighten the likelihood of it "sticking". Ideas? -Les |
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| Author: | dan [ Sun Feb 06, 2011 4:39 pm ] |
| Post subject: | Re: Miss at high RPM's |
What does the wideband do before, during and after the miss? |
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| Author: | TrevTec [ Sun Feb 06, 2011 5:23 pm ] |
| Post subject: | Re: Miss at high RPM's |
I started using Iridium IX plugs and its pretty much gotten rid of misfires on every car Ive put them in. You can gap these too, but you have to be careful because the tip is so small. I like .022 to .026 depending on the ignition system you have. I use the BR7EIX (6664) Up to about 500hp. BR8EIX (6747) For cars with 500-700hp. Over 700hp use the BR9EIX (3981). Basically go 1 step colder every 200hp over stock. |
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| Author: | dan [ Mon Feb 07, 2011 12:27 am ] |
| Post subject: | Re: Miss at high RPM's |
I've had nothing but issues using iridiums. $1 coppers for me. |
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| Author: | TrevTec [ Tue Feb 08, 2011 10:49 am ] |
| Post subject: | Re: Miss at high RPM's |
Quote: I've had nothing but issues using iridiums. $1 coppers for me.
These ones work, let me put it this way, these ones work on cars with E85, 2150cc injectors, 67mm+ turbos and 40+ psi of boost. Not only do they work, they last 10 times longer than a copper plug.
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| Author: | fastasleep [ Wed Feb 09, 2011 9:54 am ] |
| Post subject: | Re: Miss at high RPM's |
I'll switch to the iridiums.........cheap test, ya know. Anything else you can think of? -Les |
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| Author: | fastasleep [ Mon Feb 14, 2011 8:29 am ] |
| Post subject: | Re: Miss at high RPM's |
Tried the iridiums; same problems exist. Also, I changed my 750cc injectors for a known, good set of 650cc injectors and the same problems exist. Next, I suppose I'll try to change the injector resistor pack although I've never seen one go bad..... -Les |
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| Author: | 93'TSIColt [ Fri Feb 18, 2011 1:51 am ] |
| Post subject: | Re: Miss at high RPM's |
i would check and verify good grounds at the ecu.. make sure the voltages and alternator are working properly..... try taking out the MAFT or GM MAS and go back to a mitsu MAS and see if that helps.. and also eliminate the safc as well to eliminate that as the problem... why dont you just go speed density or just used a eprom socketed and a burned chip? |
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| Author: | fastasleep [ Mon Feb 21, 2011 1:14 pm ] |
| Post subject: | Re: Miss at high RPM's |
Yes, that is my next step; eliminating the MAF and AFC. I am hoping to try that in the next week. I can go to a socketed ECU, but would need a good dyno sheet to give to who is burning my chip so that they could see where I need or don't need fuel/timing. The car won't run cleanly up to the redline, so I'd be giving a bad reading to base the tune off of. Thanks for the help! -Les |
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