[DeTomaso] NPC but It's An Intriguing Problem In Any Case And It's A Ford! (kinda)

[Chris Difani]

Guys:

I've about run my head into the wall on this problem... at speed. 

And this is what's brought this disgusting state of affairs about.

Children.... 

Ah yes, you say. Children the root of all despair, delight, and aggravation. 

So, to the details. 

My daughter (the "children" in this event) has a 1998 Ford Probe GT V6 with 5 speed manual tranny. She loves this car. She's got 160,000 miles on it. And it has never failed her... until that one moment of a month ago. That's when the heater hose separated, and she didn't notice the results as she was on the freeway... at speed. It wasn't until she slowed (below 70) for the off ramp that she noticed the faint wisps of steam curling around the seams of her hood. And that led her to scan her instruments, that showed her temp gauge happily pegged past the "H for Big Trouble" point.

That was the beginning of this trail of tears.

The end point is here. And the "between" has included: replaced the head gaskets, all the coolant hoses, vacuum hoses, and all other gaskets that were part and parcel to the disassembly/assembly process for the head gasket replacement. 

Then there was the usual "Murphy Moment" when the distributor failed. No relationship to the overheating event, it just picked this absolutely, and totally unrelated moment to fail. That was diagnosed, and replaced. 

At this point we are here, and this is our problem... or the symptoms. All 6 cylinders have good compression. The engine runs, but it has a "bad" miss. There are 2 cylinders that are not firing. We've ascertained this by pulling the sparkplug wires off of the cylinders in sequence, and discovered that there are 2 cylinders that had no effect on the rough idle.

Now as to the "why" for those two cylinders not firing. First of all, their sparkplugs are firing. No question about that (and they've been replaced with known good plugs). The injectors are receiving their electrical trigger signal (NOID light test). The sparkplug wires have been replaced. There is no problem with air flow. 

The reason for our suspicion of the injectors is that the spark plugs on those two cylinders are dry. Not a drop or even a hint of a drop of gasoline on them. Nothing like the other plugs. 

We replaced that injector rail. On this 2.5L V6, (same as the Mazda 626), the injectors are enclosed in a "rail" housing, that has the fuel plumbed into one end of the rail, connected by a flex hose to the other bank's "rail", and then to a pressure regulator, and back to the tank. We replaced the rail, and we still have those same two cylinders not firing, and totally dry. 

As an observation, these two cylinders, these two "dry" cylinders, are at the end of the fuel flow circuit. The fuel intake is on the other rail. In fact, the fuel pressure regulator is located immediately next to these two "dry" cylinders. If I number these injectors with No. 1 being "upstream", at the fuel inlet, and No. 6 being the absolute farthest from the fuel inlet, my two "dry" injectors are Numbers 5, and 6.

Since we've eliminated, thru replacement, observation, or testing, all the other possibilities, I believe that my problem is these two injectors. And since I've physically replaced these two injectors with known good injectors, and I still have the problem, then there must be some other cause, either "upstream",. or downstream of these two injectors, which is causing them not to operate. Due to the nature of an IC engine, I'm at the point where I believe the problem lies in fuel pressure, or fuel delivery, or in some other fuel related issue that I am ignorant of.

Or, to say it more clearly, something's keeping these two injectors from working correctly. 

With this all in mind, I have a question or two. First of all, do electronic injectors need a minimum fuel pressure before they will flow any fuel? If this is true, does anyone have a rough idea as to what that pressure is? These injectors are 12VDC, 14.4 ohm, and flow 15 lb per hour. 

My plans for this coming week are to temporarily plumb a mechanical fuel pressure gauge into the flex connecting hose (that hose that connects the two injector rails, between injectors #3 and #4). And replace the fuel pressure regulator (if I can get my fat fingers into that very small space). 

So thank you for your forbearance, and hopefully your knowledge, and intuition. I hope that one of you will be able to point me into a successful direction... and I'll be able to get this little car running smoothly again.... (not to mention out of my shop!).

Thanks all,

Chris

Chris Difani
'73 L #5829 "LITNNG"
The Electric Pantera
Sacramento, CA
Email: cdifani at pacbell.net