4.0 OHV Idle Issue

[lowsinthe20s]

Just rebuilt a 4.0 for my B2. Just got the radiator hooked up and started to let it run for a bit. I have something weird going on with the idle. Starts up and revs to about 2500rpm then calms down to about 1300rpm, but if I hit the gas a little say up to 2000rpm it stays at 2000 and doesn't come back down. The throttle is not stuck. It just seem to want to run there.

I believe the idle are control is good. I can unplug it and the truck shuts off. Cleaned the TPS and the MAF and didn't seem to change anything. Vacuum lines all seem to be good. This is a EGR truck so it has all that crap as well.

The only vacuum line I'm not sure of is the one on the throttle body. Where does it need to plug into? Right now it is plugged. Even unplugged it runs the same way.

Thanks for the input.

 

[RonD]

If engine stalls when you unplug IAC Valve then there are no vacuum leaks causing the high idle, and throttle plate is not loose/weak spring

On startup it should REV every time, then drop
With key on the computer boots up and opens IAC valve all the way for startup
On startup, RPMs higher than 400, the computer will start to close IAC Valve to set idle, thats what the REVing is from

Cold engine can be 1,100-1,500rpms idle depending on ECT sensor(and outside temp)
But should start dropping to target idle pretty quickly over the next 2 to 4 min
Automatic warm engine target idle is 750-800rpm
Manual 625-675rpm

Do you have the 4.0ls CEL(check engine light) hooked up and does it stay off after startup?

What year is the 4.0l Computer?
Assuming Calif model, or 1995+ if it has an EGR system

 

[lowsinthe20s]

No check engine lights.

Engine is a 94 and so is the computer.

I'm not sure on the history of the motor or some of the parts used in it. I did rebuild it but I reused some of the existing parts. I do know it has JBA headers, and is bored .30 over. Not sure if it has a different cam or not. Sounds camed at low idle. At 750-800 the truck sounds like its about to die. 1100-1200 seems to be the smooth zone for this motor.

Is there anything I can do to adjust the idle?

Do you know what the vacuum port on the throttle body goes to? I just have it plugged now.

Thanks

 

[RonD]

How are you determining the RPMs?
It should idle down to 600rpms and be smooth

Not for nothin' but I still miswire coil packs
3 4
2 6
1 5
front

The 5 6 4 side can get switched around, so misfires like it has a "cam"
And thats the side that bites me in the butt

 

[lowsinthe20s]

The RPM gauge in the truck.

Yes the coil pack is wired right. now the cylinders are 4 5 6 on the driver side correct?
or

6
5
4

Is my timing off?

Do you know where the vacuum line on the throttle body goes?

 

[RonD]

Ford V6 numbering
3 6
2 5
1 4
front

Ford Coil pack firing order
3 4
2 6
1 5
front

Vacuum port on throttle body is "ported" vacuum, and was used for the EVAP system
Ported vacuum operates the opposite of "regular" intake vacuum
Ported vacuum is low at idle, and has more vacuum as air flow increases
Regular vacuum is high at idle, and gets lower as throttle plate opens

Ported vacuum is found between throttle plate and air cleaner
Regular vacuum is between throttle plate and intake valves

EVAP system pulls air/gasoline vapor from the gas tank when driving and the gas is sloshing around
So ported vacuum is good to use for this
In later years pressure sensors and added valves and solenoids were added


To balance any multi-cylinder engine the cylinders are set up in Matched Pairs
In a V6 there would be 3 Matched Pairs
The "match" means these 2 cylinders are both at top dead center(TDC) at the same time
In a V6 each pair would be at TDC 120deg apart, 3 pairs 360deg cycle
So the rotating mass of the engine is balanced

4.0l, and 3.0l, uses this firing order 1-4-2-5-3-6
This tells you the Matched Pairs that Ford uses, and it works on any firing order to find the matched pairs, 4cyl, V6, V8 or V10
Take the first half and put the next half below it
1-4-2-
5-3-6
Those are the match pairs used to balance this engine
1/5, 4/3, 2/6

That's why the coil pack looks like this
[3 4]
[2 6]
[1 5]

Ford uses waste spark so only 3 coils are needed, both 1 and 5 share a coil and spark at each TDC but only one spark is used to ignite air/fuel mix, so other spark is "wasted", hence the name, and no it has nothing to do with emissions, lol, its just a simpler way to set up a spark system, its actually the very first spark system invented for gasoline engines back in the 1890's

 

[lowsinthe20s]

Got it. Thank you for the explanation.

Question on the cam synchro should my timing be a issue. When using a timing light should the TDC line be inline with the crank sensor or should it be on the 10 degree mark before TDC? Or should it be 10 degrees after TDC?

Thanks

 

[Gonesh]

Not sure if you found the issue yet, but I’d recommend you check engine coolant temp in scanner. I’ll bet it says -40 deg. That’ll mean unplugged or bad coolant temp sensor. I had the same issue on my 98, took a minute to figure that one out.

 

[lowsinthe20s]

It was the cam synchro. Needed to be pulled out and timing adjusted.

 

[Kirby N.]

It was the cam synchro. Needed to be pulled out and timing adjusted.

What is this procedure?

 

[rhekman]

What is this procedure?

The cam synchronizer on the 4.0 OHV is at the back of the block in the center of the V, and consists of a distributor drive base, and a hall effect sensor top. It needs to be clocked so the sensor closes its circuit 10 (or 12 I don't recall exactly) degrees after cylinder 1 is at Top Dead center on the compression stroke. The book procedure is to put a piece of 34mm tape past the TDC mark on the front harmonic balancer, then check the sensor to make sure it triggers when the timing pointer reaches the end of the tape.

The 83-11 Tech Library has a how-to aricle.

Ford 4.0L Camshaft Synchronizer - The Ranger Station

Original poster: Jaymegriffiths Original Thread: Click HERE Difficulty: 7-9 out of 10 (depending on circumstances) Time to install: With engine out: 10-20 minutes / Engine in vehicle: unknown (estimated 45 min) Disclaimer: The Ranger Station.com, The Ranger Station.com Staff, nor the original...

www.therangerstation.com

Note that '94 and '95 OHV motors have a "window" sensor with marks where you can see the vane and the connector points up. Other motors will have a non-windowed sensor with the wiring oriented to the side.

I have pictures of the 94/95 style sensor and tips on using a multimeter to check the sensor in a previous forum post

Camshaft synchroizer

After I have found top dead center on my motor how do I set the camshaft synchronizer before putting it in

www.therangerstation.com

 

[Kirby N.]

Thank you. I appreciate the information. My 1991 4.0 has no sensor on the oil pump drive gear. Its just flat on top with no plug. With this in mind, I assume I don not need to do this procedure.

 

[RonD]

Correct, cam sensor was added to meet emissions requirements
In 1993 for 4.0l in Calif.
In 1995 in all states

 

[Kirby N.]

thank you