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| 88GT Road Race car build with a 3.4TDC (Page 4/18) |
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darkhorizon
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JUN 15, 12:23 AM
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Random update:
Spent many hours today trying to figure out my hesitation/misfire. Its a really goofy issue that Ive had since I started it up on this new motor. It runs fine parked, its really jumpy driving it around, like when I touch the throttle sometimes it runs normal sometimes it stalls for a few seconds then lurches off. Then once it lurches it runs fine but severely lacks power until exactly 4000rpms, then it gains 150+hp for a second then quickly starts losing it... By about 5500rpms its not making enough power to accelerate anymore if its in 3rd gear. I raced all weekend with this problem so its not "super bad" because of how it works perfectly fine at 4000 rpm and tolerable up to 5000... but its really dumb having this powerband. I would say the beginning of the day the first day it ran fine but down on power from 2500-4000rpms, until eventually now its so bad it wont run there.
To fix it ive tried changing the tune wildly, 20% more fuel everywhere, 20% less fuel everywhere, basically wildly varied it rich and lean while still being able to drive, no change, although i think leaner is slightly better than richer.
I noticed the knock sensor is reading alot of activity at most any non idle event. I easily disabled it in the tune so its not changing timing, but it still runs the same.
For what its worth, this is a 94 motor with a cam sensor and a crank pulley sensor (which i removed). I am still using the 91-93 ECU in its stock form. I had to move the knock sensor from the old motor to this motor, and I really think I did an ok job of torquing it down to spec, but i understand this can be a bit tricky.
Also, the fuel system sat for awhile, like 8 years or something, without any significant care, which is the direction i'm heading tomorrow with a fuel pressure test. I had it in my head that it wasnt a fuel pressure issue before I went out to the shop today.
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La fiera
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JUN 15, 07:40 AM
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Is there any way for you to record and see live data?
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darkhorizon
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JUN 15, 07:55 AM
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| quote | Originally posted by La fiera:
Is there any way for you to record and see live data? |
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Yes, I was logging all of these. I was able to observe the knock data and validate all of my pertinent sensors (TPS, MAP, RPM, VSS) this way. I was ready to put my wideband in as well but the wild extremes of AFR were clear on the oem narrowband. I am not tot he point of running well enough to need this.
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Joseph Upson
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JUN 15, 09:05 AM
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| quote | Originally posted by darkhorizon:
...For what its worth, this is a 94 motor with a cam sensor and a crank pulley sensor (which i removed). I am still using the 91-93 ECU in its stock form. I had to move the knock sensor from the old motor to this motor, and I really think I did an ok job of torquing it down to spec, but i understand this can be a bit tricky...
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I'm assuming you removed the crank pulley sensor because it is not required for the ECM you are using. I recall vaguely that some of these motors incorporated sequential fuel injection, which switched to batch fire after a certain rpm, although I never dealt directly with any code masks where that was in use. The consistant 4000 rpm change suggests to me that this is a switching point for something in the ECU. The closest thing I can relate to it involves a modern swap where a motor was cutting out at 4000 rpm. It turned out to be a rev limiter kicking in because during the swap, an associated sense wire was left disconnected causing the PCM to believe the motor was being revved in neutral.
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darkhorizon
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JUN 15, 09:15 AM
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| quote | Originally posted by Joseph Upson:
I'm assuming you removed the crank pulley sensor because it is not required for the ECM you are using. I recall vaguely that some of these motors incorporated sequential fuel injection, which switched to batch fire after a certain rpm, although I never dealt directly with any code masks where that was in use. The consistant 4000 rpm change suggests to me that this is a switching point for something in the ECU. The closest thing I can relate to it involves a modern swap where a motor was cutting out at 4000 rpm. It turned out to be a rev limiter kicking in because during the swap, an associated sense wire was left disconnected causing the PCM to believe the motor was being revved in neutral. |
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This is using the old 1991 style ecu, which is just a single crank sensor. I am finding the opposite issue and that it has a rev limiter at 3000rpms, and runs fine once it gets to 4000, lol.
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msweldon
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JUN 15, 01:00 PM
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Have you checked cam timing? The PO may have done the 6* or even 13* cam advance mod for more top in. Driven one like this before and they're quite testy till 4k and above...
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darkhorizon
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JUN 15, 01:16 PM
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| quote | Originally posted by msweldon:
Have you checked cam timing? The PO may have done the 6* or even 13* cam advance mod for more top in. Driven one like this before and they're quite testy till 4k and above... |
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no, but it idles pretty good. I would also expect that it makes more power as the RPM go up as well, which it clearly doesnt. Its making less than 50hp by the time it makes it to 6000rpm.
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Will
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JUN 15, 02:41 PM
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| quote | Originally posted by darkhorizon:
Random update:
Spent many hours today trying to figure out my hesitation/misfire. Its a really goofy issue that Ive had since I started it up on this new motor. It runs fine parked, its really jumpy driving it around, like when I touch the throttle sometimes it runs normal sometimes it stalls for a few seconds then lurches off. Then once it lurches it runs fine but severely lacks power until exactly 4000rpms, then it gains 150+hp for a second then quickly starts losing it... By about 5500rpms its not making enough power to accelerate anymore if its in 3rd gear. I raced all weekend with this problem so its not "super bad" because of how it works perfectly fine at 4000 rpm and tolerable up to 5000... but its really dumb having this powerband. I would say the beginning of the day the first day it ran fine but down on power from 2500-4000rpms, until eventually now its so bad it wont run there.
To fix it ive tried changing the tune wildly, 20% more fuel everywhere, 20% less fuel everywhere, basically wildly varied it rich and lean while still being able to drive, no change, although i think leaner is slightly better than richer.
I noticed the knock sensor is reading alot of activity at most any non idle event. I easily disabled it in the tune so its not changing timing, but it still runs the same.
For what its worth, this is a 94 motor with a cam sensor and a crank pulley sensor (which i removed). I am still using the 91-93 ECU in its stock form. I had to move the knock sensor from the old motor to this motor, and I really think I did an ok job of torquing it down to spec, but i understand this can be a bit tricky.
Also, the fuel system sat for awhile, like 8 years or something, without any significant care, which is the direction i'm heading tomorrow with a fuel pressure test. I had it in my head that it wasnt a fuel pressure issue before I went out to the shop today. |
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Do you have a big (~10ga) ground wire to the coil pack baseplate installed?
A Northstar missing that wire will *NEVER* run right... I @$$ume other GM DIS systems need to be similarly grounded.
The Northstar needs the big wire because the coil pack mounts to the valve cover, which is rubber mounted--and thus electrically isolated--for noise reduction.
How well grounded is your coil pack? Do you have a phenolic intake spacer?[This message has been edited by Will (edited 06-15-2020).]
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darkhorizon
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JUN 15, 05:34 PM
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| quote | Originally posted by Will:
Do you have a big (~10ga) ground wire to the coil pack baseplate installed?
A Northstar missing that wire will *NEVER* run right... I @$$ume other GM DIS systems need to be similarly grounded.
The Northstar needs the big wire because the coil pack mounts to the valve cover, which is rubber mounted--and thus electrically isolated--for noise reduction.
How well grounded is your coil pack? Do you have a phenolic intake spacer?
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I dont think there is much grounding the base of the coil pack, its basically ziptied randomly to some hunk of scrap aluminum. I'll ground it better asap.
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darkhorizon
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JUN 20, 10:33 AM
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Will, I made a much better bracket and tested that with some slightly better results of spark, it feels like it ran much better on a quick test drive. I also grabbed a spare set of coils and IGN module.
Fuel problem was found last night, likely the source of all my engine related problems... I cleaned the aftermarket fuel filter out and found a ton of junk which prompted the fuel tank drop. I knew I should have done this from the start but I tend to be overly lazy until stuff starts to really line up as the problem. 100% of the 3800 stuff I've done with fieros would shown absolutely no chance of even running at all if I found this in the tank. Pretty amazed to be honest.
"fuel pump jacket" melted onto the fuel sock, which also turned to goo.
Ruined pressure line
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