Low vacuum/rough idle post 5.0 swap | Ford Explorer Forums - Serious Explorations

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Low vacuum/rough idle post 5.0 swap

fastpakr

Well-Known Member
Joined
February 18, 2005
Messages
703
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City, State
Roanoke, VA
Year, Model & Trim Level
99 4wd - 5.0/4R70W/BW4406
Now that the (2nd) rebuilt 5.0 is in the truck (my '99 Ranger) and everything is connected, I was excited to fire it up again 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.

I'd love to hear suggestions on what I might be missing.
 



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If not a vacuum leak my thought is that the camshaft is mistimed.
 






What changes does it have to the entire stock engine, every part? The cam, rockers and timing chain set are new, how about the cam synch, lifters, pushrods, balancer, plus/wires, and what intake and gaskets are on it?
 






I'm guessing the timing chain is installed straight up, dot to dot yes? Did the cam synchronizer line up easily with the tool?
 






A camshaft timing issue was mentioned to me separately - that's definitely a possibility. I assume the shop put the timing set in straight up, but I can't guarantee that?

I didn't have the tool handy for the cam synchronizer, but my understanding was that you could bring the engine to TDC compression on #1 and install it so that the pointer was centered in the window. Let me know if that was incorrect.

Cam synchronizer and sensor are new Motorcraft units that I installed the first time the engine was rebuilt a few years ago.
I'm not sure what model lifters were installed this time - I paid a local shop to do the reassembly and they ordered a new set.
Plugs - I can't remember what they are to be honest. I installed them a couple of years ago with the original rebuild and they were still in great shape (and ran fine then).
Wires are a new replacement set of stock Motorcrafts (again, from two years ago).
The balancer is a Powerbond that you recommended here in a previous discussion as a good stock replacement. I can't remember the model off the top of my head.
Intake is the stock GT40 unit with felpro gaskets.
 






Okay, the parts all sound relatively new. The cam synchronizer needs to be installed with the proper tool. Doing it any other way is like setting the timing on a distributor by listening to it as you adjust it at idle, people used to do that. The timing is surely off by a lot, 10-20 degrees, it's impossible to eyeball accurately to one degree, which it needs to run right. So get the tool for the 99-01 302's, and that is likely the issue. You could loosen the cam synch and play with it by hand just a little, making it run better until you get the tool. But don't skip the tool, it is important.
 






It should idle with the IAC disconnected.

Ford Racing

Idle Setting Procedure

Please Note: These steps MUST be performed in sequence!!

1. Get engine to operating temperature.

2. Disconnect IAC (Idle Air Control) Solenoid. If engine stalls, turn throttle-stop screw in one full turn and restart. Repeat as necessary until engine will idle with IAC unplugged.

3. Set idle using throttle stop. Idle speed will vary depending upon modifications made to the engine. Set to where you are comfortable with idle speed.

4. Set TPS (Throttle Position Sensor) anywhere from .96 to .98 volts. This is done by loosening the mounting screws, and lightly rotating TPS. If you cannot obtain the desired range, you may need to make the mounting holes slightly larger. This can be done by drilling them.

4a. TPS wire colors to be probed are generally BLACK and GREEN wire or the GRAY/RED and GRAY/WHITE, depending on your vehicle.

5. Stop engine. Disconnect negative terminal battery cable for 15-20 minutes. You may wish to tap the brakes or turn the headlights on and off a few times as this will help to ensure that you have purged any remaining electrical current from the vehicle.

6. Reconnect IAC Solenoid

7. Reconnect battery cable to the negative terminal

8. Restart engine.

9. If problem persists, inspect for mass air meter problems and possible vacuum leaks.
 






Note for the idle set screw, do not touch it unless you know it has been messed with, or unless you know it's the problem.

If the cam or distributor timing is wrong, the idle speed screw is not the answer to fix it. Be sure everything else is right before touching the idle screw.
 






"It will not idle with the IAC unplugged"

I am thinking the idle is rough due to timing as well, perhaps the synchronizer, but there is no reason not to set the idle properly and according to Ford procedures???

It could be as simple as doing this procedure, it is standard procedure, why not? It can be done again and again if needed as you change engine power adders and it should be done. I have never had an issue doing this to set he idle properly.
 






Okay, the parts all sound relatively new. The cam synchronizer needs to be installed with the proper tool. Doing it any other way is like setting the timing on a distributor by listening to it as you adjust it at idle, people used to do that. The timing is surely off by a lot, 10-20 degrees, it's impossible to eyeball accurately to one degree, which it needs to run right. So get the tool for the 99-01 302's, and that is likely the issue. You could loosen the cam synch and play with it by hand just a little, making it run better until you get the tool. But don't skip the tool, it is important.
My understanding of the CPS was that it was primarily used for fine tuning of the sequential injection timing, but that ignition events could be handled off the crank sensor. That at least mirrors my previous experiences with an out of position synchronizer. It set a code, but there was no impact on drivability at all.
 






You may be very used to that idle set screw procedure, but not many people are. I would have to look it up, I have as yet never had to do it, never needed to.

If the cam or distributor is in wrong, than any crutch to make it run better will not fix the issue, and then the idle set screw has to be adjusted later, a 2nd time. That is a waste of time to me, if I know the cam synchronizer is set incorrectly. Do the big things first, and the last resort items, do those last.
 






My understanding of the CPS was that it was primarily used for fine tuning of the sequential injection timing, but that ignition events could be handled off the crank sensor. That at least mirrors my previous experiences with an out of position synchronizer. It set a code, but there was no impact on drivability at all.

I am the type of person that goes by the most experienced knowledge, not simply by the books. Obeying simply everything written in books and manuals etc, is a huge negative to me, I trust people more than books.

But I don't scoff at all proper manual facts and procedures, I use them as guidelines and try to follow them, up to a point. I don't buy the idea that the cam synch is trivial, if it is, yank it out and plug the hole.

Given the lack of tool setting of that cam synch, I would not do anything else until I knew that was right. It may not change how the engine runs, then I'd be looking at an intake vacuum leak. But until it's an emergency and no tool is possible, I'm going to try hard to fix that.

If someone messed with the idle screws, that could be a problem too. Which is why they should not be touched unless for the right reason, and only adjusted by the proper procedure.
 






It sounds like having to give gas to get it to start hot is too much fuel, not an IAC problem. I see your still fighting this, have you tried swapping injectors or narrowing it down to cylinders? I've seen a stuck open injector make it act like that.

Unless there's a cam correlation code then the cam sync is close enough to run. It can be shifted side to side though making it a few degrees off if you have the teeth right.
 






The injectors were sent off to be serviced and balanced while the engine was in the shop, so presumably not that.

I can try to pull plugs the next time I get to the shop. Probably Thursday at lunch will be the first opportunity. That would also let me do a compression test to see if the issue is localized to any particular cylinder.
 






Get a obd2 dongle and download forscan. You can watch each cylinder on a graph on it and help narrow issues. Short term fuel trims would be nice to know also
 






Get a obd2 dongle and download forscan. You can watch each cylinder on a graph on it and help narrow issues. Short term fuel trims would be nice to know also
That's a good idea, any additional information can help.
 






I'll do that. There's a dongle plugged in already, but I haven't fired up forscan yet. Torque doesn't work on my new phone so I've been poking around in a different app called Car Scanner.
 






There's one other potential problem here that I'm hesitant to even acknowledge...

When I built this engine the first time around, it behaved very similarly. That was eventually diagnosed as having the wrong cam - I took off the front cover and raised the body enough to sneak the cam out under the core support. Turned out Amazon had sent me a TFS cam in the correct Comp box (I assume someone returned it that way and they stuck it back on the shelf). They made good on it and sent me the correct Comp grind, and ultimately didn't make me return the TFS unit.

I'm starting to have nightmares about the possibility that I somehow handed the machine shop the TFS cam when I took the parts to them a few months ago. The easiest way to confirm is to dig through my storage unit until I find whichever cam didn't make it into the engine.
 






Did this combination need any change of the pushrod lengths, a little or a lot? I'm assuming the new cam had less different lift than the old one, and decent amount would need a different pushrod.
 



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Yes, the first time around when measuring everything it required a different set of pushrods from stock for the new cam (TFS). I don't remember which set I had to use with the replacement cam when that was shorter. The machine shop set things up this time and there were roller rockers added to the mix, so it wouldn't be immediately obvious which cam they were working with based on that.
 






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