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Discussion Starter #1
2003 Zetec / 4F27E wagon. Stock electric system - no big stereo with amps or subs. No lighting or other modifications.

My issue is belt chirp / slippage accompanied with annoying engine vibration / shudder during very specific conditions. That being: warmed up, idling in Drive, with a heavy electrical load where the GENMON PID (via ForScan) reads over 90%. I assume that's basically a "full-fielded" condition.

Background: I've had this issue for about 6 years and 120K miles of ownership. I've been through nearly every component on the car, including rebuilding the entire engine. It currently has 251K on the odometer and we just took it across Texas, NM, and AZ. It runs superb 99% of the time, yet this issue persists.


I have observed my other focus ('03 SVT) will also full-field the alternator at idle with a lot of accessories on, to the point where voltage will drop below 12V even (stereo, lights, AC, rear defrost). Perhaps it needs an alternator replacement, but it's not dragging down the engine like in my wagon.

I've checked the basics - power and ground side voltage drops. The battery cable is a new OE part. I've replaced the alternator, fans, motor mounts, battery, belt, tensioner, etc.

What I'm theorizing is that this is a programming issue around idle speed. My SVT desired idle speed (DSDRPM )is 848rpms when hot. My wagon's DSDRPM is 768rpms when hot and in Drive. Further, desired voltage (GENVDSD) on the SVT is 13.54v. The wagon is 14.48v

It seems to be perfectly synched with GENMON percentage. When alternator load is low, it's nice and smooth. Once it spikes, I'll get a shudder. Power braking the car while it's exhibiting the issue makes it stop, and it never exhibits the issue above ~850 rpms.

Fixes:

-Hi output alternator?
-Larger pulley to decrease engine load but create voltage drop at idle? I don't live in the city or spend much time in traffic FWIW.
-Smaller pulley to increase output at idle but keep the computer from demanding a full-field condition?
-Ask Tom to bump idle speed up and also lower desired voltage from the alternator?
-Or something else I'm missing?
 

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Not one word about a/c here and the primary dragger of all zetecs down to a low idle.

I have 3 zetecs and all have the shake issue which is unbalanced engine as the causer there. The alts all show 14.0 volt or higher at idle and do nothing to shake the car, it is only when the a/c comes on that the car tries to shake.

The engine will not shake at all at 900 rpm down to maybe 750 then it's all points south after that, 725 will begin to and 700 and lower gets into a solid shake. The awful pass side engine mounts are supposed to take care of that but don't. The older the engine gets the worse the shake becomes a problem because the older engine loses the 'uumph' to power through short drops in rpm that make the engine drop just enough to shake if older. The recover to PCM idle speed is slower as well.

On the ones I have the a/c is what does that, nothing the alts do will provoke it. The a/c on of course ramps the alt up in charging.

If somebody changed idle seek speed to 800 or 850 in a tune that would help tremendously. It would make emissions higher though, why Ford won't do it.

I have gotten rid of a lot of it by bumping the TB butterfly open a bit more to force the IAC to come at adjusting the idle backwards, instead of absolute idle set too low and IAC bumps it open more (much more shaking going on there) I set absolute idle a bit too high to force IAC to choke back to get to the PCM idle speed, it helps a bunch with the shaking. The IAC takes a second to do its' thing and the engine is shaking or not depending on where it is at that time.

Be careful, that is how you get an idle hang but there is a little bit of room to adjust there, you can tell as your throttle off braking will drop some as you adjust higher.

The entire issue is one of the major nuisance things I have griped about in the past, Ford doing just enough to get a new car into the public's hands to then do nothing after to make any problems better. The whole idea being to make people get tired of the issues even though car still runs and how they get past the problem of 300K lived cars cutting down on their new car sales numbers. Look at the duratec, once they figured out the mounts contributed to long term car dissatisfaction among zetec owners they then used the exact same design idea on all the engines used after. In the '70s the engineer that came up with that would have been fired instantly, no, today rather we let him design the transmission that will not work (DCT) and then choke the American people for many years with it instead of dropping it as garbage like a logical company would.
 

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Discussion Starter #3 (Edited)
I can force the issue to occur without turning the AC on. When fans are on high (Cyl head temp 115* C), any more load like lights or blower fan or lowering a power window, will make the engine shudder. Now, it doesn’t drop rpms hugely, but IAC is compensating to keep DSDRPM.

I don’t buy the balance issue, because it will often idle lower, I’ve seen DSDRPM be below 700, even 550 under certain winter conditions and it’s quite smooth. The car makes good power, gets good economy, and doesn’t burn oil. It has a fresh valve job now, new rings and bearings. I don’t think I can blame it on a tired engine.

Also, I forgot to mention, having the fans come on sooner might also help the issue. Low speed isn’t engaged until 112* C. I pretty much never see this issue below that temp unless the fans are still running.

Also, being a wagon I believe compounds the issue. It feels like I’m inside a beating drum, it’s just hitting the right harmonic frequency to drive me nuts.
 
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