TC mark=not TDC?

[patrick718]

Quick question for you guys here:

I needed to replace the FPR on my truck (which was running otherwise fine) and while I was in there I replaced the spark plug wires and plugs and it no longer starts. I pulled the cap off and set the crank at TC on the pointer- I noticed that it was pointing to the wrong spot, not the #1 cylinder. Since it appeared to be in time before, I set the #1 wire on that post and threw the rest of the wires on in order. Now the truck does not start but will eventually backfire. Is there a chance I actually didn't hit TDC? Am I 180* off?

 

[RonD]

Welcome to TRS

On all 4-stroke engines the crank shaft must rotate TWO times for one full turn of the Cam
4-strokes of a piston
compression stroke = piston is going up to TDC
(spark plug fires)

Power stroke = piston is going down to BDC
(adds power to crank shaft)

Exhaust stroke = piston is going up to TDC
(exhaust gas is pushed out)

Intake stroke - piston is going down to BDC
(new air:fuel mix pulled in)

Back to compression stroke
So #1 piston/crank have two TDCs in one full cycle

The Cam is what determines the "stroke" not the crank, piston just goes up and down, what Valves are opened and closed is what determines the stroke, and that's run by the Cam.

Distributor is driven by the Cam so it must be set for Cam timing, not crank timing.
Since there is no "Cam timing" mark visible the next best thing is the Crank timing mark
But there are TWO TDCs for #1 piston, compression stroke and exhaust stroke

If engine was already timed you could put crank at TDC and then look at distributor rotor, if rotor is pointed at #5 then you are on the exhaust TDC for #1, if rotor points at #1 then you are on compression TDC, the one you want.
If pointed at #5 then rotate crank one full turn and rotor will be pointed at #1 with crank on TDC
The Cam is what can be 180deg out, i.e. pointed at #5 instead of #1

#1 and #5 pistons are BOTH at TDC at the same time, one on exhaust stroke the other on compression stroke, they just switch back and forth from the Cam Timing


I was told that the TFI distributor has a #1 cap position that needs to be used, so you shouldn't swap spark plug firing order on the cap.
This has to do with the hall effect sensor in the distributor and the tone wheel it reads as distributor shaft spins, i.e. the wheel has #1 position IDed so computer can time fuel injectors

 

[patrick718]

I was told that the TFI distributor has a #1 cap position that needs to be used, so you shouldn't swap spark plug firing order on the cap.
This has to do with the hall effect sensor in the distributor and the tone wheel it reads as distributor shaft spins, i.e. the wheel has #1 position IDed so computer can time fuel injectors

Thanks for the help! So I am definitely 180* off.

I hate to question this, but is that true? The engine did run before and I did not touch the timing, I don't see why it would have issues now.

 

[RonD]

adsm08 mentioned that one time
That the TFI distributor tone wheel did have a #1 marker/position
As far as spark it wouldn't matter, it was for sequential fuel injection

The Rangers, 1994 and earlier, all used Batch Fire injection not sequential, so also shouldn't matter, although it could get you slightly better MPG, but so slight it almost not worth mentioning