I have a 1994.5 F250, 7.3l PSD. I've installed the 320 amp alternator from Mechman as seen here with a 3/0 charge cable. Upon startup, the alternator is "surging", or turning off and back on rapidly. This can be seen in this video: https://drive.google.com/file/d/1Y_U...ew?usp=sharing. The glow plugs are on during this video and the alternator's surging load is enough to effect the idle.

The surging is real, verified by a DVM. It is jumping from battery voltage (no charging) to 14.9v. After the surging stops, it stays steady the rest of the drive. I called Mechman and was walked through various troubleshooting procedures, including checking for high resistance on the wires going to the alt. I was sent a smaller pulley and installed a shorter belt as it was suspected the alternator was slipping due to glow plug load. When none of this helped, I sent the alternator back to Mechmans and the alternator tested fine on their bench, however, they said they installed a new regulator just to be sure. I was told that this is a problem with my truck and to stop bothering them with this. Upon receiving the alternator back, it still surges.

Today I was able to swap alternators on another 94.5 F350. I put the stock alternator on my F250 and the Mechman on the F350. The alternator surges on the other truck and the stock does not on mine. I have been very hesitant to ask for help on this issue as I do not want to give Mechman bad publicity as they are a fairly well respected company, but I am running out of ideas fast and do not believe there is a problem with my truck at this point. The last conversation I had with Mechman absolutely left me with the impression they are no longer wiling to help with this issue.

Sadly I do not understand electrical systems well enough to know what could be causing this. While I would love to be able to put this back on Mechman, I need solid evidence to do so and may not succeed.

All ideas are very appreciated!

 

I think it is still the belt slipping. As the batteries recharge or "fill up" after the initial crank, the load on the alternator decreases, so the belt stops slipping. I think their idea of a smaller pulley and a shorter belt was wrong though. I larger pulley is going to turn the alternator slower, giving it less output at idle, which should help the belt slipping problem as well as the larger pulley has more surface area for the belt to get traction.

I am thinking you are having the same problem as the guys with older single v-belt trucks run into when they install a later 130 amp 3G alternator that had a serpentine belt, and expect to get full output from a 130amp alternator on a single v-belt. It's just too much load for the belt and their trucks are fine except right after starting they get belt squeal. I am wondering if you have found the limit for the serpentine belt. 320 amps is a lot of power, and your batteries may be demanding a lot of that right after a starting cycle.

I think there are some experiments you can run to see if the belt is really slipping. After you get it running I would spray some belt dressing on the belt. 3M spray adhesive may work also. Then turn the truck off and let it sit, so you are sure it is going to surge. Then start it and see if the surge is still there or is improved. This is not a permanent solution, but can point the way to what is going on.

Is this one of those one-wire wonders? Or do they give you the option to put a remote sense wire on this alternator? If they do, I would install that and experiment with it in different spots in the electrical system.

It's just too much of a coincidence that it does it right after start up, but quits doing it after a few minutes running

 

The slipping definitely seems plausible, but I doubt that is the case at this point. I have about 700 miles on this alternator now and see no evidence of belt slippage in the form of belt debris in the pulley grooves or debris flung around. I would expect the nose of the alternator to be covered in belt debris by this point if it was slipping. There is also no noise. I would also expect reduced output while slipping, not this near "digital" on/off that it is doing. While I do have the 7 rib belt , Mechman did state that this truck is not prone to slippage at this level of output. Max glowplug output is 180 amps, measured from my amp meter. This alternator is supposed to produce 200 at idle, hence my reasoning for getting this version. From my point of view, if the truck's belt system cannot handle this, Mechman has no reason to be selling this and even greater output "bolt on" alternators. I did Google this issue and did find multiple 7.3's with HO alternators and no real mention of belt slippage or this surging style issue.

It is not a 1 wire wonder, it does connect into the factory harness. It is an aftermarket case, but resembles the original and bolts on in its place, outside of the beefier output wire.

Whatever is causing it absolutely does occur at high loads. I have a set of brand new batteries in the F250. The F350 has batteries so old and junk it barely cranks on an 85 degree day. I was not able to notice a difference in the surging between the trucks, despite one needing quite a bit more alternator assistance.

The other interesting thing which I forgot to mention earlier is this surging is not consistent. Sometimes the alternator will not surge at all, despite the glow plugs kicking. Sometimes it is only 1 or 2 blips and stops, others it will go on for a couple minutes. It does not appear to be temperature related. I've been fighting this issue since last November and have started the truck from 10 degrees to 90 degrees with no change in the apparent randomness. Because this alternator puts out enough at idle to cover the glow plugs I can't say for sure when they turn off anymore, but based on my experience at these various temperatures (had the truck for 17 years), the alternator stops surging before the GP turn off sometimes, after they turn off occasionally, and sometimes does not surge at all.

Now that it is nearing 90, this gives me the idea to disconnect the GP relay, remove that high load, and see if I still get surging. This will narrow down if it is a load issue or something weird is happening during startup/initial powerup of the alternator.

Edit: I disconnected the glow plug relay and attempted a start. It surged on the first attempt, however, it was a "mild" surge compared to most. I'll need to repeat this test a dozen more times to say for sure if this made a difference since it is somewhat random, but the fact it still surged at all with the primary load removed surprises me and raises more questions. The only drain then was recharging the batteries due to cranking alone, so this really makes me doubt belt slippage. It also makes me doubt the regulator cycling (like tripping a auto reset breaker) under high load. Mechman said they ran the alternator on their bench at full load for an hour without issue and changed the regular itself for good measure. If this is to be trusted, it does bring my setup and 2 trucks into question. What could be wrong on the truck side that would affect this alternator on both trucks, but not the stock one? Belt slippage or the alternator is not properly wired/receiving the correct inputs are all that comes to mind. I can pickup some belt dressing and give that a go. Is there any other way to check for this?

Without knowing what regulator they use, I am not sure how to check to ensure it is wired correctly. Mechman supplied the jumper harness to go from my factory wiring to this alternator.

 

I wonder what alternator they use as the base for the alternator you have? They sell special regulators with what is a called a "soft start" for charging problems right after cranking to help control belt slippage. Here's a link that has a bunch of regulators for sale. They call it "LRC" or Load Response Control.. Mechman I guess never offered you that option to try?

https://alternatorbrush.com/collecti...ord-alternator

 

Yeah, Mechman never offered an LRC regulator to me. This is the first time I've heard of that, but electrical is not my forte. This took an embarrassingly long time, but I figured out what regulator it uses. a PLFS delo style. From what I've gathered, this should be wired as follows:
P - Pulse/tach, not needed here
L - Warning light, needs 35-500 ohm resistance on this circuit
F - Output to ECM, not needed here
S - Sense circuit, direct to battery

I have wired to the L and S circuits. I'll dig out my FSM and make sure I have the right wires going into the right ports. I am not sure yet how to check resistance on the L circuit, but that does appear to be critical to regulator function. I could wire in a 50ohm resistor or so into the adapter Mechman provided, ensuring I have at least above the minimum at all times. I did find some soft start PLFS regulators, so this does appear to be a good experiment to try as well.

I am a bit confused on the F circuit as I seen some references to an internal bridge/connection between the L and F circuits, which then require 5vdc input to the L terminal. I have no idea if that is the case here, but that would not make any sense in this application.

Thanks for the continuing help and ideas. I have a direction now.

 

I am not too familiar with this newer type alternator/regulator, but most alternators need a signal from the ignition switch to bring the alternator/regulator "online" for charging. This is so it will not run the battery down with the key off. On all the ones I am familiar with, they used a terminal very much like the "L" terminal you describe. On the original system (maybe your truck had this) Ford used a lightgreen/red wire that came from the instrument cluster. Inside the cluster it was hooked to one side of a indicator light that was not grounded. The other side of this light was hooked to ignition on power. When you first turn the key on but not start the engine, the voltage would be low on the lightgreen/red regulator terminal side of the bulb, but high on the ignition switch side of the bulb. This would light the bulb. When the engine started and the alternator had output, the side of the bulb that was low would rise up to 12v. Since you have 12v on both sides of the bulb in the cluster, the light would go out. For any reason the alternator side of the bulb went low, (thrown belt, alternator failure, engine stalls, etc.) the alternator side of the bulb would go low and turn the light on. Ford also put a resistor around this bulb, so the alternator would still work if the bulb happened to burn out.

I was wondering if this is the same scenario with your "L" terminal?

 

I believe I finally figured this out. The GP relay is cycling at the same rate as the alternator. I found this in the book:


The regulator is set to 14.9v. The stock alternator runs 14.2v, no GP relay cycling. Swapping alternators causes it to cycle. I am pretty confident this is the issue now. I am going to call Mechman tomorrow to see if they have any recommendations on a lower voltage regulator, but otherwise this is my next step. 14.9 is getting to the upper end of the spec anyway.

 

I called Mechman to see if they have any advice on this issue and received an incredibly rude response. Evidently they have sold hundreds of these alternators with no issue, so I am just incompetent. I even offered to send in the documentation from Ford showing over 14.5v causes a GP protection event, but was shot down. He specifically said he didn't care, I and my documentation were wrong then hung up. I was willing to pay for another regulator, but "there are no other options".

To their credit, he offered a refund. I am taking it and go back to a stock alternator on this truck. I would absolutely not recommend Mechman alternators for the glow plug relay 7.3's as their voltage setpoint is over Ford's limit. However, I would not recommend Mechman at all due to their incredibly rude customer service. I was sent to the owner in the end who was even worse than those that answered the phone. They didn't know the truck was 7 rib, they didn't know the correct diameter of the balancer (for rpm calculation), and they don't know or care about the voltage setpoints. I'll give them credit for the refund, but that is all.

This long drawn out situation is finally resolved.