7.3L Msifire
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7.3L Msifire
1999 7.3 has been running fine until recently. The engine seems to misfire, skip, when cold. One, maybe two cylinders. Rhythmic. No Check Engine light. This when first cruising steady at moderate freeway speed, maybe 1700 RPMs. At speed, it commences when the cruise control throttles back slightly.
Stops skipping during easy or hard acceleration. Starts again on throttle back.
Quits skipping altogether once the engine warms up.
Starts fine, idles fine. Engine is well maintained. 245K. Doesn't burn oil. Still gets 19 MPG open road. Automatic 4X4.
Any thoughts?
Would also like to know a good ODC reader that will work with this vintage. Tried a cheap Actron, then an expensive Bosch. Wont read the PCM protocol.
Phil
Stops skipping during easy or hard acceleration. Starts again on throttle back.
Quits skipping altogether once the engine warms up.
Starts fine, idles fine. Engine is well maintained. 245K. Doesn't burn oil. Still gets 19 MPG open road. Automatic 4X4.
Any thoughts?
Would also like to know a good ODC reader that will work with this vintage. Tried a cheap Actron, then an expensive Bosch. Wont read the PCM protocol.
Phil
Lead Driver
Joined: Jul 2003
Posts: 7,406
Likes: 52
From: Wheatland, Mo
There are quite a few readers that will work but MUST be specific for these trucks. Although ODB II, for some reason not all ODB II readers work.
Depending on what I am looking for I use either Torque Pro or FORScan.
As for the the misfire, there are many sensors that can cause this, or low HPOP oil level, or engine oil level. Old/word injectors.... The list can go on.
I would start with the HPOP oil level first to see if it is getting/holding the correct oil level needed to run smoothly.
Once you get a good reader for your truck, run a buzz test on the injectors. This may help you locate a weak injector if that is the issue.
Then there is the sensors on the HPOP and the drivers side head that you can check. Many ways to go. Try the easiest first and see if that starts pointing you in the right direction.
With no CEL, there probably aren't any codes stored to research off of but a reader nonetheless is a good tool to have.
I am sure others will jump in here pretty quick with more info.
Depending on what I am looking for I use either Torque Pro or FORScan.
As for the the misfire, there are many sensors that can cause this, or low HPOP oil level, or engine oil level. Old/word injectors.... The list can go on.
I would start with the HPOP oil level first to see if it is getting/holding the correct oil level needed to run smoothly.
Once you get a good reader for your truck, run a buzz test on the injectors. This may help you locate a weak injector if that is the issue.
Then there is the sensors on the HPOP and the drivers side head that you can check. Many ways to go. Try the easiest first and see if that starts pointing you in the right direction.
With no CEL, there probably aren't any codes stored to research off of but a reader nonetheless is a good tool to have.
I am sure others will jump in here pretty quick with more info.
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Joined: Oct 2018
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Thanks BillyBob. It's running full level of fresh Delo 400. So low HPOP oil level seems unlikely. Recently replaced the Injector Pressure Regulator. Old one was original. Does the HPOP need to be bled of air following IPR replacement? Lost a bit of oil between the old and new IPR. Yes! I need to get a compatible ODC reader. Would love one that can plot data. Phil
Logistics Pro
Joined: Oct 2011
Posts: 3,953
Likes: 120
From: Mcdonough, GA
Why did you replace it? Did you use OEM IPR or aftermarket? These engines do not like aftermarket sensors / electrical parts. Lots of threads about new parts not working at all or inducing new problems only to be fixed by installing OEM.
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