Dropping cylinders under boost

The TPS just arrived and will try that when I get home. Hoping this will be it. Will follow up tonight.

Well it is not the TPS

I will log the fuel pumps on the way to work with the rail pressure but don’t think that it’s a fuel problem.

Guess will try the COPs like others have said. What would be the best way to do this? Replace all 8 and be done with it?

I wish this thing would throw a code or something to help.


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Normal cylinder compression on the 5.4 is ~150 psi. Unless you're running cams, I don't see the 5.8 being that far off that mark. You may want to get a bore scope and take a look at the cylinders and tops of the pistons. If you think dry cylinders have something to do with your readings, repeat the process on a warmed up engine. As a side note, the PCM is pretty effective at ratting out misfires and the ability to do so by cylinder.

Catmonkey said:

Normal cylinder compression on the 5.4 is ~150 psi. Unless you're running cams, I don't see the 5.8 being that far off that mark. You may want to get a bore scope and take a look at the cylinders and tops of the pistons. If you think dry cylinders have something to do with your readings, repeat the process on a warmed up engine. As a side note, the PCM is pretty effective at ratting out misfires and the ability to do so by cylinder.

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I thought stock compression on 5.8 was in the 170 to 180? Could be wrong though. Hopefully someone would has done a compression test on a healthy 5.8 can chime in.

While the 5.8 has a half point more compression, it does have a bit more aggressive cam timing over the 5.4. The stock cam lobe centers are fairly retarded (i.e. late closing intake) which contributes to low cranking compression.

I am hopping my readings were just low on the gauge that I had.


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well, the good news is the gauge that I was using reads about 18 to 22 lbs low. Tested it with air pressure from a regulator. Tested it 3 times with different pressures.

While at the dealership one of the techs has a very nice Shelby with KB blower and we looked over my car and found what may be causing the issue. Car now has 29k on it I have put 3k of those on it. It still has the stock belt (may be the original) with a Steada upper adjustable stock tensioner. There is so much belt dust under the snout and the belt has tons of play in it.

Well I am going to adjust it a little and get a Gate green belt or I have seen some blue belts that would look better. Please let me know if this would be the right size? 83.0 10 Rib Gates Heavy Duty Green (13' TVS with 2.4 Pulley)

I have seen some blue belts on here too but not sure who makes them. I hope that this is my issue.

Err still having the breakup or dropping cylinders. Going to order a belt and a couple COPs and rotate them around.


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LavaSlide said:

Err still having the breakup or dropping cylinders. Going to order a belt and a couple COPs and rotate them around.


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Definitely a odd issue, I'd put new plugs in with the new coils.

Way back when I had a Vortech on my 01 I was chasing what I thought was a miss. After I sold the blower and did some other things I discovered the tensioner wasn't applying full pressure to the belt. So my guess is it was slipping under boost. But the needle on the boost gauge didn't bounce or anything. It was just low. But I figured the blower couldn't keep up with my engine at the time.

JMO, but I'd pass on the green belt and go with the RPM belt. The green belts are designed to run 100k on fleet trucks. So they're stiffer and don't grab the pullies as well.

Well I don’t think it’s plugs as both sets do the same thing. I have ordered these https://www.summitracing.com/parts/FMS-M-12029-4V
and will do this this weekend.
Just looking for belt options now. The belt that is on it looks like the original belt.


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Someone I follow on YouTube, just went through this same problem on his GT500. Had a miss under boost, changing plugs didn't fix it. Turned out to be belt slip. New belt and tensioner, fixed it.

She lives. Changed all 8 COPs and beast mode enabled!

Still have some belt slip but that’s the least of my worries right now. I just have to figure out what belt to go with. From what I can tell is it may be an 84 inch belt.


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Good news! Glad you found the issue


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Green belt, they stopped making blue and RPM belts just $$$ for no benefit.
-J

Well, the belt slip is gone now. A friend that has a shop local had a Gates RPM belt just sitting on the shelf. Big win for me. Now to find a way to get some traction lol