Won't go above 2500 RPMs, completely stumped - any ideas?

Hi, I am posting this because I am completely stumped.

I had to replace a head gasket on the driver side, but went ahead and pulled them both and had them done over at a machine shop. I reinstalled them, following standard procedure, and buttoned it up, connecting everything (I was careful about marking every hose and wire, and nothing is hanging loose).

It seems to idle fine, but when driving, it essentially won't go above 2500 RPMs. It almost seems as if there is no advance.

I know the timing is correct - I have since pulled off the timing cover and the camshaft marks line up when at TDC. I seem to have spark all around - I have replaced the spark plug wires and even hooked up an analog induction timing gun and cylinder 1 and 2 are firing.

Strangely, OBDII says 'random misfires' and misfires in 2, 4, and 6, which really has me confused. I put a dowel on injector 2 and it sounds like a normal injector.

Is this consistent with any kind of sensor failure? It worked fine until the head gasket failure. But it did sit a while - I got injured right after pulling it apart and it sat 8 months. But I can't understand what would have changed over that period in terms of the electronics.

Could it be the gas? Could the machine shop have mixed up the cam gearing? As far as I can tell it only fits together one way. Otherwise I am stumped.

 

Possibility something to do with the anti-knock sensor (bad, disconnected, being “faked out” by another vibration like cam chain slack)? Since you had everything apart and the OBDII codes are dealing with even numbered cylinders on the same side, you might check that out.

https://shop.advanceautoparts.com/r/advice/car-technology/what-is-a-knock-sensor

 

Sounds like a crankshaft position sensor. I've heard of them going bad with no CEL.

 

Check the crankshaft timing cog. It's possible for it to wear a tiny groove with the woodruff key and this allows it to have play. You can check it by trying to turn the lower belt, if you have play in the crank cog then that's your culprit. Should have zero play.

 

Hmmm. If it idles ok and works fine up to 2500 RPM and only cylinders 2, 4, and 6 are getting random misfires, I wouldn’t think it would be crankshaft position sensor. An issue with the sensor would more likely be evident at idle, would show up as erratic timing with a timing light, and would affect all cylinders.

 

Any bad crank sensor I've dealt with the problem has magnified with RPM. Truck would idle fine and run well until about 2500 RPMS and then run like ass. Just my experience.

 

Might be. My experience is with ‘70s engines, no sensors, no fuel injectors, no computers. Just a distributor driven by the camshaft, breaker points and a vacuum advance. If it pinged, you just put in the expensive $0.45 a gallon 100 octane premium gas. Problem solved!

 

I just got rid of my big block 1978 Ford F250 4x4 and boy do I miss the simplicity!

 

This was kind of my thought. But the sensor isn't too much money, and I can replace it without tearing anything open again, so I will give it a try.

 

The crank shaft sensor is magnetic and prone to collecting gunk and debris. The harness is also prone getting wet and shorting. I have seen it before. When they get gunked up they can give false signals. I would atleast pull it and make sure it's not covered in gunk. Also are you running quality plugs and wires?

 

The plugs are NGK (although I had to regap them, strangely). The wires are just 'Duralast' (it is what Autozone had), but they are new.

 

I'm calling fuel pump. I just am. What else would prevent going over 2500rpms and could also cause missfires? Maybe due to fuel starvation?

 

Blocked exhaust?

Edit
Just noticed this thread is old.