'low' voltage causing lean cond.

[S351 R]

Installed new 72# injectors, but goes to very lean and poor idle after car becomes full warm and the fan kicks on.

I'm noticing that the volts begin steadily dropping from start albeit slowly (14.2 down to 13.9 over 15 minute cruise). But after fan kicks she creeps down to 13.5-13.6. Car goes full lean and the idle hunts and surges. Turn off the car, and let it sit awhile, its fine again all over, and runs great for that first 15 minutes.

I've seen Batt Corr only as high as 0.8, when its at 13.6 volts or so. This is even happening with my Injector Opening Time set now to 1.2 sec. There are no other Corrections or Temp related tables influencing anything after 2-3 minutes...

Yes the 72#ers are probably sensitive at the very low BPW at idle, but "this" sensitive? Besides trying to find out how to keep volts at 14V +, is there anything else to trouble shoot?

Thanks again

 

[55Belair]

It sounds like a warm up enrichment issue. did you by chance tune the engine while it was still applying warm up enrichment? if it happens when the fan kicks in, that may also be the point at which the system removes all warm up enrichment in your program.

 

[S351 R]

55belair, nope, double checked that. All warm-up enrichment is to zero by 120* or so.

I will also add that heavier throttle input and higher up the VE table acts reasonably. It is pretty much only at very light cruise and idle.

Is 13.5 volts even considred low and what impact does the 0.8 Batt Correction have on my troubleshooting.

 

[bobc455]

351,

I did some major voltage troubleshooting in my car recently, bringing the voltage from about 13.4-13.5 to about 14.0 (same alternator!). Then I had to re-adjust most of my VE table by about 10%! Made a big difference.

Voltage makes a lot bigger difference than I would have guessed. I used to have about the same 0.8% correct that you have, but I think much more was going on. I would also see surging when the fan came on.

If you had a GM charging system, I would tell you all that I learned, but I don't know much about the Ford systems.

I would recommend trying to get your voltage up, the system really likes it. It took me 2 years to finally figure out the problems with my charging system. The built-in voltage correction of the FAST is not all that great, so you have to have some slightly-odd VE tables and A/F ratios to make up for it.

One other thing, since my car is street driven, I have my fan come on at 205 and off at 195. I have a 160 thermostat, and the fan never comes on except in a traffic jam. However when I go to the track, I change the fan temperatures to 170/165 to keep the engine cool between rounds. You may consider changing your fan temperatures.

-Bob Cunningham

 

[S351 R]

thanks bob, at least now I dont feel like I have to trouble shoot the FAST system....
I'll figure out what I have to do to keep volts up to 14+ and post the solution for any other Ford folks on here. Hope my path is easier than yours

 

[Ricky Trussell]

Bob, How about a little info on what you did to get your voltage up. I have seen on some of my logs .8 correction and in some small spots 1.6 correction. I am doing allot of work this weekend on my car to isolate my lean problem and this might help. I f you want you can email me. That is when you get time!

 

[Chuck Leeper]

Lo volts??

Some good reading on the subject can be found at www.madelectrical.com. They deal primarily w/ the GM system, and the faults caused by incorrect sensing of alt output requirements.

 

[bobc455]

Originally posted by Ricky Trussell
Bob, How about a little info on what you did to get your voltage up.

MAD Electrical is a GREAT place, the guy loves to help with electrical problems. He was a key part of the work that I did.

As you can imagine, if you take a 1969 car that was designed for a 43 amp alternator and external voltage regulator, then switch to an internal-regulated alternator, add EFI, MSD, electric fans, dual trunk-mounted batteries, and several other doodads and you effectively have a 35 year old hacked-up mass of spaghetti.

Basically what I did included:
- Increase the size of the primary wire
- Relocate the "voltage sensing" wire to a more strategic location
- Replace the (internal) voltage regulator with an AC delco regulator
- Get rid of a lot of the 35 year old wiring (and connections) that was just not intended to perform the way I need it to, even in it's original form

It was the 4th one that paid me the most dividends, but the first three are probably the only ones that apply to most people in this forum. The most interesting thing to me, was that according to MAD the voltage regulators typically used in off-the-shelf rebuilt alternators are the cheapest regulators they can find. The AC Delco regulators, on the other hand, include fairly sophistacted circuitry that includes things like temperature compensation, specific ramp times to regulate voltage after sudden changes (like an AC clutch engaging or an electric fan coming on), and the "cheap" regulators are basically on-off switches in a similarly shaped housing.

Otherwise, it was mostly just stuff that I should have fixed earlier, but because I "thought" it would all be fine I just tried to find other problems. Eventually I just broke down and started chopping through the wiring mess like a jungle-hiker uses a machete. Visually it's still not a prize-winning electrical system, but it works much better.

Also, to help clean up the mess, I used a few of these- http://www.madelectrical.com/catalog/cn-1.shtml

-Bob Cunningham

 

[ZBass28]

Well dang.....

I almost always see 13.2 - 13.6 volts out of my '96 Z28, along with the .8 batt correction on FAST. I always wondered if this was affecting performance, and in what way if at all.