Agreed but we are talking about running as though a cylinder isn't firing at all. The GPCM from what I have read is designed to keep the glow plug on in any cylinder that isn't warm enough to fire properly. This is why I questioned if his truck had the California Emissions.

My truck has this cold running problem as well but I believe part of it could be the PCM not being correct and therefore not operating the GPCM properly. When talking to someone who repairs PCMs for Ford, he told me this is a common problem since the California Emissions PCMs are difficult to find and guys swamp in the standard relay PCMs just to get them running and sold.

I don't pretend to know it all, so if one of the pros can set me straight on my understanding of the GPCM operation, I am all ears.

 

Awesome info! Thank you!
I should clarify that it does sound like it's missing in at least one cylinder when I'm driving until it's warm. Once it's warmed up for the day the problem doesn't reoccur.
I think it sounds like the injector problem Cleatus pointed out (thanks brother!) , because it runs well as long as the engine oil is warm. I'll do a buzz test this weekend.

Another question : if I ignore the problem and just have it miss until warm, will it damage anything? I have 6 kids, one in uc Santa Barbara, and don't want to spend 1200 on injectors. Thoughts?

 

Cleatus is the guy to ask on that.

 

OK, ran buzz test this morning and in two cylinders the buzzing is very muted. I did the same thing at around noon (warm oil still) and they all buzzed fine. That shows me that you were right, Cleatus (thank you!), so I have a few more questions if you don't mind. It only lasts about 5 minutes where it is not running on all cylinders. What should i do? Do I replace the injectors, shim them and hope for a few more miles, ignore the problem until the injectors fail completely?
Also, if I do replace the injectors, I have heard a lot about 160/80 injectors. Do I need to have tunes already in place to run them, or can i run them on stock tune, and will it affect my smog tests?

 

It's not going to hurt it to run it that way. I've been running the service pickup at work now (2000 F550) with this problem for almost 4 years and it sits outside most of the time. Most mornings are never much higher than 50 degrees in the summer and I don't start plugging in the block heater or parking it inside the shop until it's been below zero a few mornings.

When it's really cold, it'll run rough for a few miles even after it's been running outside for 5-10 minutes at 1300 RPM with the backpressure valve closed. Once the oil warms up though, it's usually good for the rest of the day.

One temporary fix that may get you through a couple of winters' worth of cool temperatures is to run 5W40 synthetic engine oil. It's really good at curing "the romps" in the morning for those that experience that anomaly too. Unfortunately, the symptoms of worn-out injectors will not go away on their own and as I said before, shimming the armature plate will buy you a little time with little more than <$100 and a couple hours of labor.

To run 160/80 injectors you will need custom tuning to keep your sanity while driving. The first 1/8 of accelerator pedal will be like an on/off switch for idle to 12-1300 RPM and it will suck. It will not hurt anything to drive normally like that, but it will idle rough for a few seconds after stopping and it will smoke badly (but run like a striped-*** ape) when you put your foot in it.

 

As far as smog goes, you will definitely need tunes in order to pass smog with 160/80 injectors. With proper tuning and an otherwise healthy truck, you won't have any problem passing.

However make sure your truck looks stock when you get it smogged. Gauges are fine to have, but remove as much evidence of the chip as you can. If you get a PHP (which I'd recommend) remove the controller and tuck the wiring behind the dash.

 

Is there a step above stock injectors that doesn't require tuning?

I plan to send my PCM in for repair or replacement soon. After that I will be looking at increasing performance. Would it be best to wait on changing injectors until then?

 

An option that most people miss out on are stock split-shots with larger nozzles. No tuning really required and great power on stock tuning. I've tuned a couple AD/80% trucks and that's what I'm doing to one of my personal vehicles when I get the ambition to pull the injectors (not an easy task on the '73-7.3L). They run terrific.

 

Cleatus and Andym, your information is awesome, and thank you!

I almost feel like ive gotten off topic a bit, but even though I've read dozens of threads on injectors, I don't quite understand the difference between them. I understand that the split shots are stock style, to reduce noise, and that the 140 vs 160, etc is the size of the maximum fuel event. Other than that, I am a bit ignorant of what the percentages do, and the value of single shot and 80 versus 100% etc. I have 248k on the same injectors, and while they are working warm, I know injectors are in my future. I like performance, and have guages (and a crappy bully dog chip mod, which I will upgrade to a hydra when i do injectors). I just want to make sure I am getting the best bang for my buck.

Thank you for sharing your knowledge with me! I am constantly amazed at the knowledge and how many on here have the heart of a teacher.

-Dave

 

What size nozzles would you recommend?

 

Well said, and I agree completely.

 

80%. No other option in my opinion.....but it's only an opinion.

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​​​​​​​As I understand it, 80% means they can inject 80% faster? That would be critical at higher rpms right? Why do the injector companies list so many 30% injectors? Those aren't fast enough? Or am I misunderstanding?

 

The "80" means the nozzle is 80% larger than stock. 30% nozzles don't really give you that much improvement. Also, the only nozzles that are manufactured by Alliant are 0% (stock) and 80%. 30% and 100% nozzles are adapted by the aftermarket.

Larger nozzles will help decrease EGTs when pulling a heavy load up a grade in a lower gear/higher RPM. The larger nozzles inject the fuel more quickly and efficiently, and it has time to complete its combustion cycle before the exhaust valve opens.

Note that cleatus is a genuine expert in this field. What he says, goes!

 

Just because I am overly opinionated and extremely hard headed doesn't mean I know it all. The only thing I will say is that after 9 years of tuning, I have come to realize that these trucks should have come with 80% nozzles from the factory and everyone would have been a lot happier.