chastings

89 renix 4.0 aw4

Sometimes when I crank my cherokee it cranks a little bit slower than usual (just slightly), the tachometer starts jumping around, there will be a slight cough, the cranking speed slows then it stops cranking completely. I turn the switch off and try again and it usually starts the next try. It doesn't always do this, maybe once every 20 starts or so.

The battery is a new napa legend with new cables. I tested the crank sensor a few months ago. It showed .4 ac volts indicating it is weak--also, when I unplug the crank sensor it cranks much faster.

Since it tested marginal I think I'll replace the crank sensor and see what happens. But this is such a bizarre sequence of events it seems that I may have another issue that's contributing to my starting issues.

When this occurs it seems as if it's trying to fire at the wrong time during the start sequence throwing off the crank speed. Fwiw it runs fine, no issues other than an occasional hard start

Thoughts.....

chastings

Also installed a new ignition switch for a separate problem. Occasionally accessories like a/c and radio would quit working... New switch fixed that, but it did not address the hard start.

cruiser54

Of my Tips, which ones have you performed completely?

DFlintstone

I think .4 is OK. Don't be in any rush to change the CPS. I'm not sure what meters read what, at what rpm, but a .4, slow or fast cranking I think is OK.

"it cranks a little bit slower than usual"** "cranking speed slows then it stops cranking completely."
Those are not sensor issues.

Battery gasses have a nasty habit of helping a thin, hard crust form on the bat post's and clamps. They can look pretty good, but that micro-thin layer is a surprisingly good insulator. SHINNY! Lead is what you want. I use a pocket knife, (gently), for the insides of the clamps. For the posts I might use one of those post cleaner wire brushes, but still scrape it with a blade. If you have a condition where you have power, (dash lights ect.), then when you hit it power goes out altogether, that's a common result of a layer of oxidization there. Btw, a half *** connection could be expected to get hot during cranking, or while it's trying. Cleaning those is something to do now and then anyway, so if you are having starting problems, you might want to make sure you have bare lead on lead. Might save you some grief!
Then, at the very least, at least check your grounds. You can chase your own tail all day trying to figure it out and get nowhere if you don't have good grounds.

CrawdadSlim

And don't forget to place a shiny copper penny on the battery haha.

DFlintstone

I hadn't heard about that one. As it happens I have had almost no corrosion on (alot), of batterys for about 15 years.

cruiser54

Works. Super glue a penny right next to the terminal.

DFlintstone

I wonder you could buy a copper penny, and how much they cost?

cruiser54

A dollar 380.

DFlintstone

O'Rilys sells a little foil pouch of "oxy-guard" or something like that for about a buck. I'll use that on other's cars, but all of mine get regular bearing grease inside and out, all over. I've been doing it forever on everything including my house battery bank, for years. Seems to work great.

cruiser54

http://www.olypen.com/craigh/oxgard.htm

DFlintstone

Neat. Was pretty much my take but I didn't know about the abrasive. I'm not seeing even a non-conductive grease, like the dielectric, interfering with a metal to metal connection. The grease being "plastic" will squeeze aside of the metal to metal and remain to prevent any gas from corroding the connection. Would be easy enough to check I suppose.

salad

And more!

http://www.k1ttt.net/technote/antiox.html

chastings

Update. I went back through cruisers renix tips. As it turns out the ground from the firewall to the cylinder head was poor. I've cleaned on it several times before but it made no difference. After adding another grounding strap it now cranks much faster and the tach no longer jumps around during the start sequence. It was frustrating as hell since the battery was brand new, cables and terminals were brand new and I had refreshed all the main grounds prior... My best guess is that either the cylinder head stud is too hard to gain access to clean properly or the grounding strap had a loose crimp Either way it's good to go now!
Thanks!

cruiser54

Sum*****, imagine that!!

You are correct about the cylinder head stud. Just add the ground.

You wanna share the story of us knowing each other already?