Car runs great until 12/13 psi

Rick the pool guy

Active Member
Feb 7, 2017
286
191
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Massachusetts
I've been having this problem that just randomly appears,
when I drive the car normally it's fine once you get into boost say above 12-13 PSI the car falls on its face it will have a small backfire through the exhaust as soon as you let off it clears itself up it doesn't happen all the time only on certain occasions under high boost .
So what I did took it home started doing some diagnostic work and come to find out my coil pack is bad and how I found out my coil pack is bad I took my multimeter put it on ohms and tested each individual coil in the values were all over the place
6 and 3 : 9900 ohms
2 and 5: 10007 ohms
4 and 1 : 10125 ohms
New coil pack was 11400 across the board .
So I hope this helps anyone with the same problem.
Thanks for reading:RTPG
 

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Anthony P

Active Member
Jan 24, 2007
717
219
43
while the GM service manual and so many other diagnostic write-ups discuss checking coilpak tower resistance as step one in the diagnostics, it's really a crappy test that does not do much. the notion 11-13K ohms and all is OK is really not accurate.

a static test on the bench does not illustrate any potential problems that would show themselves in a dynamic test, under load on the car.

a better test under load is with Casper's C3I simulator tool. I had a thread recently illustrating the weird spark seen via that Casper's tool at lower than normal system operating voltages.

https://turbobuick.com/threads/help-interpreting-electric-arc-variations-using-caspers-c3i-to-test-coilpaks-ignition-modules.465135/

is the charging system operating normally?

can you borrow the casper's tool from someone near you? if not, Casper's should be having their annual sale in a few weeks...if same as last year. having the proper diagnostic tools like that C3I simulator makes a world of difference when trying to figure out stuff like this.

a lot can happen when coilpak under load. many times a coil can work fine at low rpm(load), but dies completely at higher rpm(load).

if there is no one local with the Casper's tool, or Cotton's is too far, for the cost of shipping both ways, you could send me both your coilpak and ignition module to test.
 

Rick the pool guy

Active Member
Feb 7, 2017
286
191
43
47
Massachusetts
while the GM service manual and so many other diagnostic write-ups discuss checking coilpak tower resistance as step one in the diagnostics, it's really a crappy test that does not do much. the notion 11-13K ohms and all is OK is really not accurate.

a static test on the bench does not illustrate any potential problems that would show themselves in a dynamic test, under load on the car.

a better test under load is with Casper's C3I simulator tool. I had a thread recently illustrating the weird spark seen via that Casper's tool at lower than normal system operating voltages.

https://turbobuick.com/threads/help-interpreting-electric-arc-variations-using-caspers-c3i-to-test-coilpaks-ignition-modules.465135/

is the charging system operating normally?

can you borrow the casper's tool from someone near you? if not, Casper's should be having their annual sale in a few weeks...if same as last year. having the proper diagnostic tools like that C3I simulator makes a world of difference when trying to figure out stuff like this.

a lot can happen when coilpak under load. many times a coil can work fine at low rpm(load), but dies completely at higher rpm(load).

if there is no one local with the Casper's tool, or Cotton's is too far, for the cost of shipping both ways, you could send me both your coilpak and ignition module to test.
I greatly appreciate it luckily I have a brand new setup, just waiting on the coil pack gasket.
This is what I love about the turbo buick community everyone helps each other. I'm a member on a different forum (Nova) and you don't get the help and knowledge that you get here .
 

Clark6

Member
Apr 15, 2006
950
10
18
48
Those 103s cost me a race once $$$ I was tuned for 1 day of cold weather but the next day temps raised by 20* or so,,, when I got a call to show up. got to the spot with the same tune as day before 1st & 2nd was gravy soon as I got to 3rd pop pop guy was leaving... got home looked at the 103s 2 was black... I put 104s in didn't have that problem since... not saying its your issue but 104s gapped .025 is much better now..but hold on I didn't see you had a fast & already tuned by Cal... never mind... this was just my experience I think my 80lb inj. dumped a tad too much fuel on the 103s. my boost may have been too low.. 24psi maybe I needed 30 lol. ( Just check em to be safe make sure they aren't black)
 
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Rick the pool guy

Active Member
Feb 7, 2017
286
191
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Massachusetts
Those 103s cost me a race once $$$ I was tuned for 1 day of cold weather but the next day temps raised by 20* or so,,, when I got a call to show up. got to the spot with the same tune as day before 1st & 2nd was gravy soon as I got to 3rd pop pop guy was leaving... got home looked at the 103s 2 was black... I put 104s in didn't have that problem since... not saying its your issue but 104s gapped .025 is much better now..but hold on I didn't see you had a fast & already tuned by Cal... never mind... this was just my experience I think my 80lb inj. dumped a tad too much fuel on the 103s. my boost may have been too low.. 24psi maybe I needed 30 lol. ( Just check em to be safe make sure they aren't black)
Thanks that's some solid information .every day I'm always learning something new
 

dank GN

BlackArts Automotive (661)993-8277
Jan 11, 2009
3,919
533
113
SoCal the high desert
Don’t know if this has been asked but what is your fuel pressure like? It sounds like your pump isn’t keeping up . I had a similar issue where the pump was fine until I got into boost around 10psi then the pressure started fluctuating like crazy . Just something to check out
 

Rick the pool guy

Active Member
Feb 7, 2017
286
191
43
47
Massachusetts
Don’t know if this has been asked but what is your fuel pressure like? It sounds like your pump isn’t keeping up . I had a similar issue where the pump was fine until I got into boost around 10psi then the pressure started fluctuating like crazy . Just something to check out
Running dual pump setup activated by a pressure switch it turns on the second pump at 13psi .definitely going check that out .
 

GNVYUS 1

Active Member
Dec 15, 2002
3,471
10
38
IL
I would get something similar that I called the alky farts due to a way rich condition under an initial wide open throttle hit and load. It went away once I leaned out the car into the low 11 range.
 

dank GN

BlackArts Automotive (661)993-8277
Jan 11, 2009
3,919
533
113
SoCal the high desert
Yes 10.5 is crazy rich . Turn your alky down you are flooding your combustion chambers. Shoot for 112-11.4 ish unless you are running some big boost 25lb plus then I would shoot for 11.0 for 28-35lbs .
 

87GNALKY

Active Member
May 25, 2018
139
37
28
Hendersonville, TN
Not sure if A/F is the issue here. But, my car only runs under 11.0 on a cold start.
Backfires are almost always lack of timing. You can run rich if you like, but better adjust timing to match or your just going to load it up with meth and fuel, hence the backfire.. Just my 2 cents on that. Sounds like a slight tune issue that may be related to atmospheric conditions changing between the tune setup not the person that tuned it to the conditions in which it was currently operating.
 
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