Misfire - Spark Occurring on Intake Stroke
After head job a friend of mine called me to check this 2004 ford expedition with misfire on bank 1. I installed the in cylinder pressure transducer on number 1 cylinder & checked ignition primary signal on number one ignition coil (coil on plug system).
The spark is occurring on intake stroke right where the intake valve opens. The vehicle has one cam sensor on bank 2. I checked cam timing, the exhaust valve opening is about 35 degrees & intake valve closing is about 40 degrees.
Why the ecm is firing the ignition coil on intake stroke? Only the right bank (bank 1) head was removed. I'm thinking wrong camshaft but still cannot understand why the ignition is occurring on intake stroke. Any ideas will be appreciated.
You mentioned wrong cam shaft,. was it replaced? It deff sounds like a cam timing issue. I would look at the old cam, and see where the key way is in relation to the first lobe on the cam. The cam gear may line up with the chain mark just fine, but that doesnt mean the cam itself is timed if theres a problem with key way.
Yes. I think the machine shop who put the camshaft , they might have put the wrong cam.
Hi Vicken, Why not reuse your old camshaft? Was it too far worn?
Oops, you are helping on this one, not actually doing the mechanical work.
Please post a scope image of the transducer/spark during cranking, running at idle and snap acceleration.
I don't have the scope images. I have to learn how to save it & post it. I have the Escope Elite 4 & i'll learn how to save them & i can post it when i visit the shop.
Did you check the ignition timing on bank two as well? May the coil connectors have been mixed up?? Do you mean the exhaust valve opens at 35 degrees BBDC and intake valve closes 40 degrees ABDC? If so, these values are within normal range. Again you may want to compare bank to bank.
I was thinking coil connectors, too. They're all identical, so maybe enough slack in the harness could allow someone to switch them up inadvertently.
Yes. I compared bank 2 and it fires on compression stroke 14 btdc. I checked coil connectors for mismatch but they're ok. What bothers me is that the cam timing are right on but the ignition is firing on intake stroke. Somehow the ecm is looking for another sensor or maybe bad ecm grounds.
If B1 was installed 180* off from B2 the cam timing would be correct and the ignition timing would be 14* before tdc EXHAUST stroke which should be about when the intake valve opens. Is this when it is firing? Or is it actually on the downward stroke of the piston? That makes a differance.
Hi Vicken, Make sure the same thing is not happening on bank 2, if it is the crank reluctor is suspect, because that is what triggers the ignition coil firing. #1 cylinder notch is what starts the firing event Early models with the external reluctor were bad about slipping on the balancer, the later models with the internal reluctor had issues if a balancer center bolt came loose/not torqued…
I don't have captures. I have to learn how to do that. But yes they changed bank 1 cylinder head and that's what the problem happened. I'll visit the shop and get some waveforms & post them. Thank you
Hi Vicken, That makes we wonder if the machine shop gave them a sedan head instead of one for a truck/van application. Not all 4.6's were the same. here were differences. The camshafts were a different profile along with different cam and crank triggers for trucks and vans. Look them up in Ford parts and you will see what I am saying.
Posting the waveform would help, posting B2 would also help. Are all cylinders on B1 missing or just 1?. My bet would be cam timing is off. Ignition timing is determined by CKP and the stroke is determined by CMP. As you said the CMP is only on B2, so ignition is set to B2 compression stroke. The engine has no idea where B1 cam is.
"Are all cylinders on B1 missing or just 1?" Exactly my question too!
I didn't check the others. I'll let u know guys. Thanks
Vicken I’d have to agree with Benjamin I wonder if coil connectors are switched or there is damage to the harness and two wires are touching each other
If 2 ignition coils connectors are switched, there should be 2 cylinders misfiring.
Sure. The OP didn't exclude this possibility or specify the # of misfiring cylinders,that's why I suggested that he may want to pay attention to switched coil connectors.
Vic, If you have a current probe and a four channel scope, you should be able to show your compression waveform, your coil firing, and all other cylinder's timing based on coil current. I think the problem will become apparent.
Ok great information. i'll do that when i visit the shop. Thank you
The vehicle is fixed. Sorry for the delay. The camshaft was off 180 degrees. Thanks for all the replies and very helpful.
Vicken Thanks for the many updates to keep us in the diagnostic mode. I was just here reading the replies again (and of course your posts) and I thought, why not wipe the “board clean”. You've given us some great information (very exact) about what the ignition even is, but I was wondering, what else do you see/measure. Can you achieve three drive cycles so we can have some mode 06 misfire…
I did leak down test and it was 8% leak. I also check the cam timing with the valve cover removed & put the special tool behind the camshaft, they're two tools one goes to the back of the camshaft and the other tools slides over the first tool & it both legs of the tool should touch the cylinder head which it does. Its driving me crazy. I have to check the other cylinders on bank one…
“I also check the cam timing with the valve cover removed & put the special tool behind the camshaft, they're two tools one goes to the back of the camshaft and the other tools slides over the first tool & it both legs of the tool should touch the cylinder head which it does. Its driving me crazy.” If you were to install B1 properly, rotate the crankshaft 360 and install B2 properly…
Hi Vicken, Have you used these tools before without issue? I ask because there have been problems with certain aftermarket copycat tools. Just food for thought. Also, does this cam have the alignment pin or is it held by a torque to yield bolt (friction fit)? Are you inspecting timing according to the chain links or some kind of tech marks that were used? These must be aligned using the links…