89 IROC 305 TPI WOT Stumble at 4200 rpm
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Joined: Oct 2008
Posts: 1,365
Likes: 216
From: PA
Car: 91/89/85/82 Z28s, 88 TA, 88/88 SC
Engine: SBC and LS variations
89 IROC 305 TPI WOT Stumble at 4200 rpm
So i am having an issue with one of my 3rd gens, it has a pretty repeatable stumble at around when i go WOT and hit around 4200 rpm
it does not always do it, but it seems to be pretty repeatable at this point
using Datamaster i did some logging (my 165 logs pretty good in this car) and as you can see in the attached pic, instead of stay PE driven rich, the 02 sensor is showing that it seems to be losing fueling at that point
a couple weeks ago this iroc died on me and i needed it toed to get home as it wouldn't restart... after i got home it did, but it was rough... it had a bad ECT sensor (-40C) so figured it was due to that and replaced that along with a bunch of other items since i was at it as car has 100K miles on it- new FPR, bosch 3 injectors from southbay, fuel filter, 180 deg t stat, EGR delete, etc
since then it starts fine, idles fine, and generally drives fine other than WOT in any gear above 4200 rpm...
i am thinking the fuel pump might be weak or strainer getting plugged, etc, and probably am just going after that, but it seems so repeatable i would think if the fuel pump it would be a little more random in how it responds...
anyways any thoughts let me know
it does not always do it, but it seems to be pretty repeatable at this point
using Datamaster i did some logging (my 165 logs pretty good in this car) and as you can see in the attached pic, instead of stay PE driven rich, the 02 sensor is showing that it seems to be losing fueling at that point
a couple weeks ago this iroc died on me and i needed it toed to get home as it wouldn't restart... after i got home it did, but it was rough... it had a bad ECT sensor (-40C) so figured it was due to that and replaced that along with a bunch of other items since i was at it as car has 100K miles on it- new FPR, bosch 3 injectors from southbay, fuel filter, 180 deg t stat, EGR delete, etc
since then it starts fine, idles fine, and generally drives fine other than WOT in any gear above 4200 rpm...
i am thinking the fuel pump might be weak or strainer getting plugged, etc, and probably am just going after that, but it seems so repeatable i would think if the fuel pump it would be a little more random in how it responds...
anyways any thoughts let me know
Thread Starter
COTM Editor
Joined: Oct 2008
Posts: 1,365
Likes: 216
From: PA
Car: 91/89/85/82 Z28s, 88 TA, 88/88 SC
Engine: SBC and LS variations
Re: 89 IROC 305 TPI WOT Stumble at 4200 rpm
so just to follow up on this thread for the sake of future knowledge, i did replace the fuel pump, strainer, etc... interestingly for a 100K car the tank inside was in great shape and generally everything was very clean and could not see any real trouble
anyways went with a high flow walbaro, deleted the pulsator, and also put in a brand new gm sender unit... after install the iroc fired right up and i took it for a test run and though initially i have this resolved, but the issue quickly returned after a couple hard WOT pulls
i thought what else could be causing this lean stumble and since it only happens at high duty cycle WOT i decided to swap the ECM thinking the injector driver might be overheating and flaking out... Bingo, since changing ECM the IROC has been performing like new and i have done a lot of WOT pulls to satisfy myself it is resolved!
anyways went with a high flow walbaro, deleted the pulsator, and also put in a brand new gm sender unit... after install the iroc fired right up and i took it for a test run and though initially i have this resolved, but the issue quickly returned after a couple hard WOT pulls
i thought what else could be causing this lean stumble and since it only happens at high duty cycle WOT i decided to swap the ECM thinking the injector driver might be overheating and flaking out... Bingo, since changing ECM the IROC has been performing like new and i have done a lot of WOT pulls to satisfy myself it is resolved!
Supreme Member
Joined: Jun 2011
Posts: 2,036
Likes: 5
From: knoxville tn
Car: 86 IROC
Engine: 5.0 TPI
Transmission: 700-R-4
Axle/Gears: 2.73 open
Re: 89 IROC 305 TPI WOT Stumble at 4200 rpm
so just to follow up on this thread for the sake of future knowledge, i did replace the fuel pump, strainer, etc... interestingly for a 100K car the tank inside was in great shape and generally everything was very clean and could not see any real trouble
anyways went with a high flow walbaro, deleted the pulsator, and also put in a brand new gm sender unit... after install the iroc fired right up and i took it for a test run and though initially i have this resolved, but the issue quickly returned after a couple hard WOT pulls
i thought what else could be causing this lean stumble and since it only happens at high duty cycle WOT i decided to swap the ECM thinking the injector driver might be overheating and flaking out... Bingo, since changing ECM the IROC has been performing like new and i have done a lot of WOT pulls to satisfy myself it is resolved!
anyways went with a high flow walbaro, deleted the pulsator, and also put in a brand new gm sender unit... after install the iroc fired right up and i took it for a test run and though initially i have this resolved, but the issue quickly returned after a couple hard WOT pulls
i thought what else could be causing this lean stumble and since it only happens at high duty cycle WOT i decided to swap the ECM thinking the injector driver might be overheating and flaking out... Bingo, since changing ECM the IROC has been performing like new and i have done a lot of WOT pulls to satisfy myself it is resolved!
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