Vehicle is a 1989 Ford F-150, 4x4, 5 Speed, 4.9L (300-6)

I've done a lot of stuff to this truck in the past few weeks since I got it. Probably the most important to note is new ignition components, everything from TFI to plugs (except the pickup coil). And also new fuel injectors.

My problem has been if I downshift to or over-rev in 3rd the CEL will blink.

From what I gather this means a misfire has been detected. Is there any other reason that the CEL blinks randomly but does not stay on?

Also, how does this vehicle detect a misfire? I'm under the impression that it doesn't have a crank position sensor?

At first I almost had to try before it would do it. Now the "misfire" seems to be getting worse (or more consistent). Lately it might do it from 2nd through 4th gear (while driving it right) and maybe in 5th at times. Like I said, I've only had the truck for a few weeks so the issue has been increasing pretty rapidly.

Let me also say that the engine runs perfectly, even when the light flashes, there isn't any noticeable loss of power or performance. It idles as smooth as silk and the throttle response is right now.

This makes me think that it's a false misfire detection, or something else is going on. Other posts that I've seen with similar issues always report the engine runs like crap, but that's not the case here.

Now, if I remove the vacuum line from the EGR Valve and drive it, I can NOT make it blink. Whether I put a plug in the vacuum line or not, it doesn't matter. But as soon as I plug it back in to the valve and start driving the blinking will continue.

The CEL has never blinked while parked, neither at idle or higher RPM sustained or punched, EGR Vacuum connected or not.

So is this a dumb question...change the EGR Valve and be done with it right?

Or is there something else I should check first?

KOEO is 11
CM was 32
KOER is 11

I've checked the codes a few times since I've had it and it's always been 11's across the board with no continuous CEL. So I chalked the 32 up to disconnecting the vacuum line, but I'm going to take a spin and see if it comes back with the EGR connected correctly. I'll post the outcome shortly.

Thanks,
Roger

 

Okay, so I just went for a 10 mile drive. CEL just flashed away between 3rd and 5th and finally stopped. And when I turned around, same deal.

The CEL never did stay on, just flashed intermittently.

I pulled the codes again...

KOEO 11
CM 31 (PFE, EVP or EVR circuit below minimum voltage)
KOER 11

That 31 looks a lot like the 32 (EVP voltage below closed limit).

FWIW, I replaced all the battery cables a while back. I also installed 6 braided copper ground straps, two 4 ga. engine to frame, two 10 ga. frame to cab, and two 10 ga. frame to bed.

I think the EVP is the thing bolted on to the EGR Valve with the wire connector. I did check those wires with the key on, according to my Chilton manual it should be 4V to 6V between VREF and SIG RTN. There's three wires there, and I don't know which is which, but I did find 3.7V +/- in one place and 4.5V +/- in another. The manual also says that thing can be tested while hooked up with the key on and 0.67V or less means the sensor is okay. I wasn't able to do that with just two hands and nothing to stand on.

So I guess I'm narrowed down to the sensor or the EGR valve itself.

Based on the fact that the engine runs perfect even when the light flashes, I'm leaning more towards the sensor being bad.

 

Your tests while might be correct chance you're not checking between the correct pins.

This will show you which is which to be sure you do,

Fuel Injection Technical Library » EGR Valve Position sensor (EVP)

Yea sounds like you are on the right track, computer is telling you the evp voltage falls below 0.24.

 

That's very helpful, I'll recheck that tomorrow. Thanks a bunch!

 

We had a break in the cold weather today so I took the chance to work on the truck some more.

I did some testing on the EGR, EVP and EVR and everything was good. More importantly, I replaced all of the vacuum lines on the engine and the problem seems to have gone away.

That doesn't really make sense because the code was for a "below minimum voltage" problem. Or maybe my fiddling around with wire connectors fixed it.

But anyway, I'll take it.