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5.0 rough idle/low vacuum


fastpakr

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Now that the (2nd) rebuilt 5.0 is in the truck and everything is connected, I was excited to fire it up last week. Unfortunately, it idles like hot garbage and I'm struggling to nail down what's going on. If anybody wants to help solve the puzzle, here's what I know:

It's a '99 Explorer with GT40P heads and headers running the entire stock wiring harness, emissions components, etc
Roller rockers (stock 1.6 ratio)
Cam (comp XE258HR-12) (info here) is pretty mild, with springs installed to match it.

Very rough idle, tends to shut off when putting in gear. Will not restart without applying accelerator halfway (but starts cold with no throttle input).
Idles at ~10" of vacuum. Power brake assist is negligible.
Tested with booster disconnected, no change in vacuum measurement.
Shuts off immediately if IAC is disconnected.

No codes are being set.
No apparent impact from spraying starter fluid around any accessible vacuum connection (front and rear trees on drivers side, power brake booster, upper to lower joint, etc).
Using a smoke machine to detect vacuum leaks didn't demonstrate any.

The fuel is about two years old. I'm looking for a 5 gallon can so I can transfer a few gallons at a time into another vehicle and run it in that, then refill with fresh fuel.
 


85_Ranger4x4

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Tried capping off where it goes to the booster?

That rogue hose to the front of the intake too.

And maybe try this:

 

RonD

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Reads like cam timing is off with 10" of vacuum
Are you sure the cam installed was the cam ordered, mild?

Do compression test on a few cylinders, expected is 155-165psi with CR of 9.0:1
 

85_Ranger4x4

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Reads like cam timing is off with 10" of vacuum
Are you sure the cam installed was the cam ordered, mild?

Do compression test on a few cylinders, expected is 155-165psi with CR of 9.0:1
Yeah, the cam ran good the first time around.
 

fastpakr

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285/75-16
I went down the road the first time with getting a different cam than I ordered (Amazon somehow shipped me a high RPM trick flow cam in a Comp Cams box), but it really ought to be the right one this time. A shop did the reassembly for me this time - it's hard to imagine they screwed up the installation, but I suppose anything is possible. For that matter, I suppose it's -possible that I inadvertently handed them that Trick Flow cam by accident...

Compression test sounds like a good idea. I should have a chance to do that later this week. Thanks!
 

fastpakr

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Tried capping off where it goes to the booster?

That rogue hose to the front of the intake too.
Yep, I've tested with both of those capped (and EGR, for that matter).

Russian Space Station approach is starting to sound better and better.
 

RonD

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Does vacuum get better holding engine at, say, 1,500rpms?

And I assume exhaust is clear as far as you know, no new changes, no potato in the tail pipe :)
No rag left in the intake pathway?

Coil pack spark wires are correct, double check

302HO and 351s used different cams so different firing order, but are interchangeable you just need to switch around spark plug wires to match the cam firing order
EDIT: Never mind on this one, with Waste spark it wouldn't matter
 
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85_Ranger4x4

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For that matter, I suppose it's -possible that I inadvertently handed them that Trick Flow cam by accident...
You might go dig under your bed and see which cam you still have...

If you find the comp cam you are kinda done. If it is the Trick Flow proceed with diagnosing.
 

fastpakr

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You might go dig under your bed and see which cam you still have...

If you find the comp cam you are kinda done. If it is the Trick Flow proceed with diagnosing.
Yeah - I was just thinking about heading to the storage unit tomorrow and searching for the cam. As much as it would absolutely infuriate me if I had the comp cam floating around there, it would sure answer the question!
 

fastpakr

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285/75-16
Does vacuum get better holding engine at, say, 1,500rpms?

And I assume exhaust is clear as far as you know, no new changes, no potato in the tail pipe :)
No rag left in the intake pathway?

Coil pack spark wires are correct, double check

302HO and 351s used different cams so different firing order, but are interchangeable you just need to switch around spark plug wires to match the cam firing order
EDIT: Never mind on this one, with Waste spark it wouldn't matter
Exhaust is clear as far as I know. No changes other than the headers in that regard. Though admittedly, the exhaust has been sitting under the truck disconnected for two years so who knows what might have built a home there.
No rag in the intake.
The coil pack to spark plug wiring definitely matches what I show for the '99 Explorer.
 

fastpakr

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For what it's worth - I didn't have the camshaft synchronizer alignment tool available when I installed the synchro. A quick search led me to believe that I could bring the motor to TDC on #1 and stab it in so that pointer was in the middle of the outer window. Assuming that I butchered that - how much would that affect things? I'm unclear on how the system handles a misaligned synchronizer in comparison to a distributor being out of position. My impression the past was that it wasn't nearly as critical...
 

RonD

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No, not critical
Crank sensor is the main sensor, cam sensor allows better fine tuning of sequential injector timing
You will get a code if computer can't sync cam sensor to crank sensor, computer can change cam sensor by a few degrees either way, electronically
 

fastpakr

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I dug through the storage unit a bit last night but had limited time. So far, the only thing that turned up was the original Explorer camshaft. Heading back for a deeper dive as soon as possible, but it might be a few days.
 

fastpakr

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You can stop wondering about the source of the problem now.

I really did screw up and hand the shop the wrong cam when they assembled the engine. The correct one was in a box in the storage unit.

Cutting the core support to allow swapping the cam with the engine in place and not having to raise the body is very, very tempting. Has anyone been down that road? @bobbywalter ?
 

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wrong cam, that sucks. feeling for you.

what a toss up question. hack the front or just remove the engine...... so much involved in a cam change.

I wish you the best of luck and post the progress.
 

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