Hi All, I'm new to the site. I bought a '91 F250 4x4, seems like it will be a great truck. Of course, finding some "Gremlins" to fix. It has the dreaded slow-cranking issue, sometimes won't start, only when hot. I began web searching and most helpful things I found were on this forum. So, I got new negative cable and solenoid to starter cable, plan to replace them tomorrow. If that doesn't do it, God I hope it does, what would I try next? It starts perfect on first start of the day and runs excellent, until I stop a couple places. All simple obvious (to me) things test good - battery, alt, starter. Already replaced relay/solenoid.

 

Welcome!

I would suggest cleaning up all of the connections. Both on the negative side and on the positive side of the starter circuit. I use a Wire wheel on a impact driver to clean up connections. Clean up the 2 small bolts which the solenoid attach to the fender. This needs to be good contact. Clean up the ground cable which goes from the battery to the fender. I put di-electric grease on after i have cleaned up the connections.


In terms of the solenoid I would try to find a motorcraft one. I have read that the cheaper ones can be bad out of the box.


I also would suggest switching to a PMGR starter if your truck doesn't already have one. I just replaced my old direct drive starter with a PMGR starter and it works great. It requires less current. Also instead of the current needing to pass through the solenoid(on the fender) to start the truck, it instead just needs to activate the solenoid on the starter. So there will be less demand for the solenoid(on the fender) to pump out tons of current. Instead the starter gets the power directly from the battery instead of needing to go through the solenoid(on the fender). Its quite easy to replace, only requires adding a new 10-12awg wire, and switching where the positive cable from the battery to the starter goes.


Yea so clean up some connections and install those parts you have. I would suggest spending a few days cleaning up every connection. Than lets hear how the truck performs.

 

One of Fords better ( worst ) Ideas is there main ground cable setup on these trucks. Follow the ground or negative cable down from battery, Chances are you will find a wrap around like clamp on the top of the frame / front cross-member. Its at this point the outside jacket of the cable is removed and this clamp type wire connector is crimped on. With no real protection the cable starts to corrode and destroy its self from expansion of the corrosion. This damage cuts the wire size going to the engine and frame as more and more strands break and corrode away. From this point the cable will continue to the passenger side of the engine block. I replace with two separate premade cables. One to the frame and a separate one to the engine block. Replace the ground clamp on the battery with a heavy duty one Like pictured.

Most good parts stores stock them. At this time it good practice to check the other smaller body grounds going to the battery. Be sure to clean all mounting surfaces to get good connections.

 

Thank you for the tips and info. I've never heard of the type of starter you mentioned. Might check into that. A friend suggested I just run another ground from battery to the block somewhere. It is hard enough to find a spot accessible on the block. I assume to a bracket, like alternator, isn't a good idea? I'm leery of messing with electrical, I don't want to do anything sketchy. I also read it could be more involved, like a stator or some module on distributor? If my new cables and cleaning doesn't solve it, I might take it in to a pro. I'm planning to go camping in about 3 weeks. I need to have things all good to go before that.

 

Those terminals look awesome. The joint you mentioned is where I think the issue is. I took truck to Napa for second battery test the other day. Sure enough, it dragged and wouldn't start when tried to leave. After a couple tries, I wiggled the negative cable a bit, tried again and it started right up as if no problem at all. So truly hope replacing that cable and starter to solenoid does the trick.

 

Here is a nice PDF showing where you can add the ground on the back of the alternator. http://www.powermastermotorsports.com/alt21_2g.pdf

This is where I added the extra ground to my alternator. It is where it threads into the alternator mounting. I didn't have the correct bolt on hand to mount it to the back of the alternator.


So end up using this bolt. This seems to be the upper bolt which holds the alternator on.

 

That looks good thanks for sharing. Another Q that I have: Is it ok to have a 2-gauge positive cable from battery to solenoid? The new cables I bought and all other cables are just 4-gauge. Is that better or does it matter? Seems like they should be the same. It had the larger positive cable when I bought it. I'm replacing that cable too while all apart, starting out fresh. Thanks!

 

I believe when it comes to 12v systems, bigger is generally better. If you can get 2 awg I would put 2 awg in.

I assume the starter is pulling something like 120amp. I believe it will be pulling more than 120amps if it is an automatic.

 

I dont kn ow about that fire hazzard there I dont own one, but the 3g(if you upgrade ) has a threaded spot on the case in the back that you can mount to. I have that and i run the ground to neg. Any size is fine, just point the cable the right way. also, that ground is barely doing anything unless you clean the mineral layer of aluminum before mounting.

I ran a ground wire to the strap on frame, I cleaneed the threaded spot area, and i have a lug on the frame THEN the oe above it, and then I have that cable add on and just help carry ground. since the engine to battery is on the alt, and the alt bracket is clean where it touches eachother, the one on the frame i put to the fender

 

So far, very good! I put all new cables on this morning and it started right up. Took several test drives, and starts fine at operating temp. It is what I call hot 100+ degrees living in central valley of Calif in August. I think this issue is solved. I think it runs smoother even better now. Good grounds is more important than I realized. I appreciate this forum, it led me to what I needed to do. Thanks for the comments and advice as well.

 

find wherever the PCM grounds and make sure that one is good. mine is core support