4.0 timing

[lilfordrunner]

How does the PCM know whether the #1 piston is at top dead center (tdc) of the compression stroke or the exhaust stroke, and does it matter?

 

[lilfordrunner]

How does the PCM know whether the #1 piston is at top dead center (tdc) of the compression stroke or the exhaust stroke, and does it matter?

 

[snake]

Probably by the cam position sensor, and it should matter... wouldn't run if it was 180 deg off.

 

[Snoranger]

It depends on the year of the 4.0l...


The ign. system doesnt care. It fires the plugs in pairs. #1 fires on both intake and exhaust strokes on all 4.0ls.

There are 2 reasons for the computer to know when #1 is firing:
- sequential injectors.
- cylinder ID.

It uses the cam sync to know that. They werent added until '93 on the cali emissions trucks and '94 on the other 49 state trucks.

 

[lilfordrunner]

I appreciate the feedback. What you are saying is, if the timing is set up correctly ( it is ) the #1 piston should be in the right location?

 

[lilfordrunner]

It's a 93

 

[Snoranger]

Are you having a problem? or are you just wondering?

 

[lilfordrunner]

Well, I did a 4.0 swap and haven't quite got it running perfect yet, turns out the timing WAS 180 off, we are assuming. So after changing that, we just want to make sure everything is in the position.

 

[alwaysFlOoReD]

On my 91 4.0, there is a crank position sensor at the front of the motor that feeds a signal to [IIRC] the edis module. With help from the ecu, the timing is figured out and sent to the coils. I can't think of how the piston could be in the wrong position with this system, but I've been wrong before, and will be again.
Hope this helps,

Richard

 

[lilfordrunner]

Thanks Richard

 

[Snoranger]

Well, I did a 4.0 swap and haven't quite got it running perfect yet, turns out the timing WAS 180 off, we are assuming. So after changing that, we just want to make sure everything is in the position.

The ign timing on a 4.0l CAN NOT be 180° off... Both #1 and #5 (180° apart) fire at the same time from the same coil on the same circuit.

If the cam sync (your truck may or may not have one.) was 180° off, it will fire the injectors at the wrong time. BUT it will still fire the coil at the right time.

 

[lilfordrunner]

So base timing and ign timing are correct with great compression. Why would it run so rich and idle so fast?

 

[Snoranger]

You need to give some more details...

From what I gather you swapped a '93 4.0l into your '87 Ranger. It runs, but the idle is high and runs rich.

How did it run before it went into this truck?
Did you hook everything up? Are you sure?
How high is the idle?
Whats your fuel pressure?
Did you do anything to the motor, or did you just pull it and drop it in the truck?
Did you remove anything that could have caused the problem? (If it ran good in the donor, it should run the same in the new body unless something is different.)

 

[lilfordrunner]

I got the 4.0 out of a 93 explorer. I completely rebuilt the engine from the block up. It was running previously, but I was already going to replace the heads so i figured in for a penny in for a pound…just redo the whole thing.

The engine its self is all built correctly. The wiring, I have to assume is darn near correct. The truck starts, it runs (rough) but dies when it gets warm.

Now that I am doing a little more research I think it may have to do with the o2 sensor.

SO!!! The Ranger has a spot for 1 o2 sensor on the exhaust, the 4.0 wiring harness has a spot of 2 o2 sensors…So, how many sensors do I need and how would I connect two if that is the case.

NOTE: I used the truck harness out of the 87 ranger and the engine harness from the 93 4.0 and spliced them together. So there are two connectors for the 02 sensors but only one spot in the ranger exhaust.

 

[FritzTKatt]

Maybe you could swap in a section of pipe from that year with the o2 sensor spot in it, and hook it up.