Low power/low vacuum

Craig0320 · Sep 19, 2018

You might have to regap the plugs with the new cam. Yes a misfire can cause a low vacuum car situation.

85_Ranger4x4 · Sep 19, 2018

fastpakr said:
Comp Cams XE258HR / 35-510-8

It says for stock HO... I have seen stuff not boxed correctly though.

And it might be something else totally different too. I guess we will find out from the shop. :icon_bounceblue:

fastpakr · Sep 19, 2018

I think the shop is done at this point. They're convinced that it's caused by the cam.

Craig0320 · Sep 19, 2018

Oh damn it does say for stock HO. I am pretty sure the 5.0 ho used the 351w firing order.

fastpakr · Sep 19, 2018

Right. All the later model 5.0's switched to that order, including the explorer engines. It's the same order as it was stock.

Craig0320 · Sep 19, 2018

Well good on that then. So I guessing the valves are staying open just enough causing a compression loss with that cam?

adsm08 · Sep 19, 2018

Do a cylinder leak down test.

fastpakr · Sep 19, 2018

Adsm - are you thinking the cam overlap is allowing too much leak down between the valves?

Craig0320 · Sep 19, 2018

That's what I was getting at in my previous post could be just enough to bleed off some compression during engine operation.

fastpakr · Sep 19, 2018

Maybe. The grind has basically zero increase in overlap compared to the stock cam, but a lot more lift. It shouldn't affect vacuum, and a lot of others have used it on otherwise stock Mustang and Explorer engines without a tune or any of these issues. It's ground for off idle gains, not high RPM power.

All that said, I'm starting to wonder if it's really the cam grind I chose, or if the wrong cam came in the box.

Craig0320 · Sep 19, 2018

I did a lot of reading also and got the same results as you did other people are running these cams without any tune I think you most likely got the wrong cam in the box.

fastpakr · Sep 19, 2018

That could explain why I've needed to use different pushrods and others didn't go through that.

Craig0320 · Sep 19, 2018

Yeah so now you have to think how much more you're opening the valves with a longer pushrods

fastpakr · Sep 24, 2018

It's not an overlap issue. Compression looks pretty solid: 145, 150, 150, 145, 145, 159, 145, 159 for cylinders 1-8 respectively.

Ignition timing is around 10BTDC on cold start, increasing to around 30 after it's warm.

My gut instinct is to wonder if I botched the cam chain installation somehow and stuck it in one tooth back (8*). That could explain the delayed power delivery. Not sure how I could have managed to screw it up, but it seems likely at this point unless someone has a better idea.

85_Ranger4x4 · Sep 24, 2018

fastpakr said:
My gut instinct is to wonder if I botched the cam chain installation somehow and stuck it in one tooth back (8*). That could explain the delayed power delivery. Not sure how I could have managed to screw it up, but it seems likely at this point unless someone has a better idea.

I was petrified of that when I did mine. What I did was I timed it the best I could and then tried it either other way off a tooth to see if it looked better.

Low power/low vacuum

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