Hello all. I am having a devil of a time with the number one cylinder on my 1993 MPFI 460 F-250.

165-170 psi of compression. Nice fat spark when the plug isn't so fuel-soaked it cannot fire. I am on the second NAPA-replacement fuel injector with both presenting the very same: some amount of fuel, FAR more than the metered amount intended, fouling the plug and creating a misfire. Fuel economy is crap, the engine runs the very same kind of poorly with either spark plug or fuel injector unplugged. Again, cleaned off, the plug does fire, it is not a spark issue, best I can tell. It is either mechanical within two injectors now, that something is preventing them from fully sealing, possibly??? Or it is further upstream within the electrical system and something is telling the injector to stay open too long.

My understanding of this EFI says that the system really isn't advanced enough to address a single cylinder individually. The injectors pulse the same amount each time.

I am hoping some member of the community can help me get past this.

Thanks to all for reading.






Jeremy

 

You can rent or purchase a noid light tester and see how its signal is coming to the injector. I would start there. Compare it’s signal to other cylinders.

 

I agree ^^^^^^^

. . . and you could try swapping this injector with any other injector. See if the problem follows the cylinder or the injector. Then swap back and see if the problem follows again.

I know you are on the second injector on the same cylinder, but this would definitely rule out the second injector.

 

I'm headed to the local NAPA to pick up a noid-light kit this morning.

I guess the other issue is that I'm leery, even if the second injector proves to be the issue, of just throwing another injector at the truck.

 

you can bench test it before you put it on with a battery and wire jumpers.

 

I did that last time with the latest injector. It passed the "ring/click" test perfectly well. The noid tester should help me isolate whether it's the injector or something upstream.

I've also seen that checking resistance is a good way to tell injector status, so I will check resistance across all injectors and see if that tells me anything.

 

That will identify a broken injector. They should all be in the ballpark of 14-15 ohms.

 

^This is what I would be doing^

 

Some more data points. I didn't want to remove all of the intake piping, so I only noid and resistance tested the passenger bank cylinders.

The resistance is a bit higher than 14-15 ohms, but it is consistent on all of the injectors, starting around 18 and dropping to about 17. The suspect injector on cylinder one does read a little bit higher than the rest, only dropping to 17.5 ohms. That is with a warm engine and most of what I've read indicates the resistance will be higher with a warm engine. Not sure what is too high though.

Similar with the noid testing. I cannot tell any appreciable difference between the suspect cylinder and the rest. It isn't like the light stays on, or doesn't go off, it flashes as close to the rest as I can tell.

I put a new plug in cylinder one today. NAPA didn't have any copper-core plugs, so it's a platinum-core Auto-Lite in that one hole. With the new plug my temperature reading on the first cylinder has come up a bit, but it's still hundreds of degrees cooler than all the other cylinders, so I assume my misfire will remain.

I am going to swap the injectors on cylinders one and two and see if the issue follows the injector or not. That will also allow me to look at the new injector alongside the originals. The bodies of the injectors are identical, similar coloring, etc, but I understand there were a couple of different options for how the actual holes are setup. I'm wondering if maybe the parts store screwed up and sold me the previous style injectors???

Beyond that, I am at a loss. The truck is still running painfully rich and backfiring through the exhaust on decel. Gas is too high right now to keep fighting this problem.





Jeremy

 

Have you held the spark plug to the block to verify fire across the gap? It could be fault in the plug wire, or distro cap as well. It’s fire or fuel. It sounds like you’re getting the proper injector signal. As long as they are all within 1-2 ohms, I would say they are good on that aspect. Could still not be closing all the way causing the foul, but electrically, I would say they are ok.

 

Verified spark. It was pretty weak with the copper-cored plug I swapped out, but nice and fat with the new platinum-cored plug... of course that's before the thing gets totally fuel soaked.

I just swapped number one and two injectors. Number one cylinder is still really cold in comparison to the other seven. Within a couple minutes of running the other cylinders read 2-300° with my infrared thermometer, right at the exhaust port and number one is still having trouble. I'm getting higher temperature readings with the injectors swapped, but still way off what the other cylinders read. Like that head tube will get up to 150° or so and no more.

I cannot imagine the compression has changed appreciably from the 160 psi is had Thursday night. It definitely has enough compression to fire the cylinder. It's getting enough air to generate compression. Has spark... at least until the plug gets fuel soaked and fouls.

I really feel like I've touched all the bases here. I'm sure whatever I'm missing will be simple and glaringly obvious whenever I find it... I'm mostly trying to eliminate as much legwork as I can in finding it.




Jeremy

 

MY next step would look to see if I had a stuck valve. That and get 4 16 oz Coke bottles and put that bank rail in them. Watch the spray cycle
while someone turns the key.

 

You need the correct year FORD WSM to go through a complete diagnostic routine.

The injector will thin the engine oil and begin to cause all kinds of issues.

Do you know the manufacturer's source of the NAPA inj? Was it new or a reman?

Better to stay with MOTORCRAFT unless replacing entire set.

 

I commend you on changing the injectors that many times because they are a pain to get too.

It takes air, fuel and spark for combustion. You have air, you have compression and you have fuel.

160 psi of compression is plenty to fire properly.

90 project 5.0 is leading you down the right path. If you have backfiring out the exhaust, something is firing a plug at the wrong time.

Get one of those cheap adjustable spark testers. You should be able to jump a spark across a 3/8” gap. Compare with another plug wire.

Check the ohm reading of your spark plug wire with a similar length one.

Check down the length of the plug wire looking for any small black pin holes where the spark energy could be leaking out. Check the boots also. If they originals, consider replacing them.

Pull the distributor cap and check for any hairline cracks inside and out. Check for carbon tracking from one terminal to another. Check for moisture in the cap.
If it has more than 30k miles on it, pitch it for a new one.

The odds of having multiple new injectors bad is slim to none unless your wiring is bad to the injector.

 

Whelp... thanks to all of the advice given here. After doing what all seemed most obvious in terms of checking for spark, fuel, compression, etc. and then swapping the suspect injector for a known good one and seeing no change...

I pulled the valve cover off today.

All eight rockers are in place and tight.

But there's only seven pushrods.

The intake pushrod for cylinder one has completely left the chat.

Obviously it didn't disappear. It's still somewhere inside the engine... but hasn't caused any damage so far.

Maybe it will loosen up from wherever it currently is at some point in the future... but right now I have a new $6.99 pushrod on order from the local NAPA and my plan is to install it and see what happens.

I know, I know, I know. I *SHOULD* pull the intake and hopefully find the old pushrod sitting in the valley. But I'm gonna put a new pushrod in and see if the valve opens. If it does, I am going to consider the problem fixed.



Jeremy