05 Taurus alternator ripple

[protraxrptr17]

3.0 2v engine
No codes. Surging idle. New IAC. Still surging. Check AC ripple. Had some spikes over the 500mv threshold. Unhooking the cable from the alternator stopped the surge. I had the lab scope hooked to the IAC checking duty cycle. Had a really strange pattern with spikes. When I took off the cable, went to a smooth line. I replaced the alternator and still have same symptoms. Same voltage spikes above 500mv. I ordered a Motorcraft alternator. Supposed to be here tomorrow. Is there anything else I should look for? Seems like the alt can be the only thing causing this.

[DougMontgomery]

Make sure alternator bracket mating surface to block is clean and tight. Make sure all engine to body gorunds are clean and tight

[greasybob]

Where are you hooking up the leads of the scope when testing ? Can you match the spikes in the AC ripple with a reference voltage from any other sensor or actuator ?

[kebo1970]

use a high amp probe with a scope so you can view the alternator ripple.

[Wheel]

3.0 2v engine
No codes. Surging idle. New IAC. Still surging. Check AC ripple. Had some spikes over the 500mv threshold. Unhooking the cable from the alternator stopped the surge. I had the lab scope hooked to the IAC checking duty cycle. Had a really strange pattern with spikes. When I took off the cable, went to a smooth line. I replaced the alternator and still have same symptoms. Same voltage spikes above 500mv. I ordered a Motorcraft alternator. Supposed to be here tomorrow. Is there anything else I should look for? Seems like the alt can be the only thing causing this.

If your battery is bad - even if it starts the car - it can cause more ac ripple and do funny things with the rest of your electrical systems, and can cause your symptoms.

[fueltrim01]

Does the idle surge stop when you unplug the alt? If not then the problem is somewhere else.

[fueltrim01]

Sorry, I did'nt read your post completely.

[protraxrptr17]

Checking ripple= Ground lead on batt neg, Pos lead on back of alternator

Checking IAC duty cycle= Ground on batt neg, Pos on control side of IAC

New alternator just showed up. We shall see.

[protraxrptr17]

Well, new alternator had a lot better patten. No spikes over 500mv, but didnt help the surging. Strange thing is, the new alternator died after running about 10 minutes. I went back to the parts store and got my original.

GEN_MON fluctuates rapidly between about 13 and 41
GENFDC(%) on startup runs about 40 at startup and then drops to zero then blinks up to 55 at pretty regular intervals.

Completely stumped right now. Cleaned all grounds, tried a different battery. What is GEN_MON? WHy do we not have fast track data scan anymore? Why do we not have generator field on/off in functional tests anymore?

[protraxrptr17]

Heres a screenshot

[protraxrptr17]

RPM and IAC

Gonna scope the crank sensor now, but dont see how that could be it.

[greasybob]

Just curious, but what are the fuel trims at idle ?Could be that if lean just decreasing the load on the engine might make the idle more stable. I've never seen an alternator do this but I have seen a dirty MAF cause idle surge when the AC is turned on.

[protraxrptr17]

Around -4 on the long term. MAF was a little dirty. Cleaned it, did nothing. What is strange is the thing will run butter smooth with the alt unhooked.

[Crusty]

Around -4 on the long term. MAF was a little dirty. Cleaned it, did nothing. What is strange is the thing will run butter smooth with the alt unhooked.

OK, so what's happening when you unplug the alternator??
It's running on the battery. System voltage is now lower. Engine load is now lower.
Several things come to mind.
As suggested, make sure the alternator housing/case has good ground, including the bracket(s) to the engine.
Voltage drop the battery cable ground and the positive cables. Both the supply cable at the starter and the smaller wire from the alternator to the battery.
While you're there, I've seen several Ford products with corrosion INSIDE the battery cable end where originally, the metal was formed around the cable core.
Put a load test (not a conductance tester) on the battery. If it's borderline or low, it can affect what the alternator and the charging system wants to do.
Verify the fuel pressure and the regulator (if it's not a returnless system)
Also I would check the TAB/IAC activity and clean the throttle plate....ya, ya, Ford's been saying it isn't necessary for years but that's just because they don't want to pay for cleaning while it's under warranty. They, amongst others keep coming up with throttle plate cleaning procedures every couple of years...LOL
Then see if there is an "idle re-learn" procedure after you clear codes. Then take it for a short drive for about 5 or 10 minutes so it can do some more "re-learning" on it's own.
Then see how the idle is, the IAC (or TAB) counts, the rpm's and the vacuum (both the MAP sensor if it has one and with the good old vacuum guage)
At least that's where I would go.
HTH
Let us know what you find.
(could the Gen_Mon mean generator monitor % ??)

[protraxrptr17]

I talked to the customer later and he said that he hadnt noticed any surging and didnt act concerned about it. I took that as he didnt want to spend the money to fix that particular problem. He brought it in for a "tune up", brakes, trans oill change and engine oil change, so I let him have it back. Wish I could have figured this one out. I will always wonder what was wrong.