Need help with slow crank

87fox72mach

Member
Nov 17, 2019
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pennsylvania
hey guys to make a long story short I bought my 87 about 10 years ago it was well modded car ran great etc I tore car apart to smooth engine bay and get it painted after getting screwed on the paint job I threw it back together to drive it. at the time of the engine bay smoothing i put the battery in the trunk added an electric Taurus fan. ever since i re did my car ive had demons the biggest pain being the car will crank slow and not start when hot after years of being fed up and finishing another project im diving back into the fox im a little wiser now and have more capital to work with. this is what i have tried so far

1.) timing- ive checked the timing multiple times its right on and the car runs like a top when its running
2.) changed starter multiple times
3) added a heat wrap blanket to the starter
4.) moved battery back to the engine bay
5.) multiple new batteries
6) ive turned the fan off when i parked it and tried to restart without fan running at all still does the same thing

I want to get this issue fixed before I rip the car apart again to finally do the car the way I intended im at a dead end anyone with any advice would help
-- im thinking is it something with the alternator which was upgraded to a 130a before i bought the car. voltage gauge on dash shows its charging while driving
 
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Glliw

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Oct 21, 2019
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You state that it has issues strating when hot, but does it also have issues when starting cold?

What is the CCA rating and group size for the battery you are using?

What are you using for battery cables and terminals? stock gauge?

How low does battery voltage dip when you are cranking?

What is the static battery voltage when the car is off and when it is running?

Have you tried starting with a battery tender connected?

Is there any visible issues with the terminals? Nice, solid connections at each location?

Are there any other electrical issues on the car?

Slow cranking is a symptom of lower power output of the starter which could be caused by too much system resistance (cables, terminals, and battery) or a weak battery, either due to a short in the system, undersizing of the battery, weak connections at the terminals, etc.
 

87fox72mach

Member
Nov 17, 2019
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pennsylvania
the car has absolutely no starting issues when I go out to start it after it cools down a long time etc over night batter is brand new and I think is 800 cca around there. terminals are brand new I have a good ground from negative side of battery to the block and a ground from block to firewall. I even added another ground and some point battery cables are 4 gauge wire which were on the car when I bought it.

yes if I put a battery charger on it and let it charge up a tiny bit more it will usually start but still cranks a little slower, no other electrical issues on the car.

the only other thing I can think of is years ago I fried a part in the ecu by jumping the hood light connector like an idiot when pulling codes I had trying to fix another issue) but it was ok after that as far starting when hot (i jumped out the cpu by soldering a small wire on the board as i found online to fix the crank no start issue)
 

jrichker

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No Crank checklist for 5.0 Mustangs

Revised 24-Oct-2013 to update voltage drop figures.

No crank, slow crank and stuck starter solenoid problems have the same root causes – low battery voltage and poor connections. For that reason, they are grouped together.
Use the same initial group of tests to find the root cause of slow crank, no crank and stuck solenoid problems.

Since some of the tests will bypass the safety interlocks, make sure that the car is in neutral and the parking brake is set. Becoming a pancake isn’t part of the repair process…


1.) Will the car start if it is jumped? Then clean battery terminals and check battery for low charge and dead cells. A good battery will measure 12-13 volts at full charge with the ignition switch in the Run position but without the engine running.
A voltmeter placed across the battery terminals should show a minimum of 9.5-10 volts when the ignition switch is turned to the Start position and the starter engages or tries to engage. Less than this will result in a clicking solenoid, or slow cranking (if it cranks at all) or a starter solenoid that sticks and welds the contacts together.

Most auto parts stores will check your battery for free. It does not have to be installed in the car to have it checked; you can carry it with you to the auto parts store.

The battery posts and inside of the battery post terminals should be scraped clean with a knife or battery post cleaner tool. This little trick will fix a surprising number of no start problems.

The clamp on with 2 bolts battery terminal ends are a known problem causer. Any place you see green on a copper wire is corrosion. Corrosion gets in the clamped joint and works its way up the wire under the insulation. Corroded connections do not conduct electricity well. Avoid them like the plague...

If the starter solenoid welds the contacts, then the starter will attempt to run anytime there is power in the battery. The cables and solenoid will get very hot, and may even start smoking. The temporary fix for a welded starter solenoid is to disconnect the battery and smack the back of the solenoid housing a sharp blow with a hammer. This may cause the contacts to unstick and work normally for a while.


A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection while trying to start the car: more than .25 volts across a connection indicates a problem. The voltage drop tests need to be done while cranking the engine. It's the current flowing through a connection or wire that causes the voltage drop.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .



Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch or solenoid
100 mV Ground
0.0V Connections
A voltage drop lower that spec is always acceptable.

2.) Check the battery to engine block ground down near the oil filter, and the ground behind the engine to the firewall. All grounds should be clean and shiny. Use some sandpaper to clean them up.

3.) Jump the big terminals on the starter solenoid next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.

The rest of the tech note only concerns no crank problems. If your problem was a stuck solenoid, go back to step 1.

4.) Then pull the small push on connector (small red/blue wire) off the starter solenoid (Looks like it is stuck on a screw). Then jump between the screw and the terminal that is connected to the battery. If it cranks, the relay is good and your problem is in the rest of the circuit.

5.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then you have wiring problems.

Typical start circuit...
Diagram courtesy of Tmoss & Stang&2birds


6.) Pull the starter and take it to AutoZone or Pep Boys and have them test it. Starter fails test, then replace it. If you got this far, the starter is probably bad.


Starter solenoid wiring for 86-91 Mustang



Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.
[


Electrical checks for the switches and starter solenoid

Remove the small red/blue wire from the starter solenoid. Use a screwdriver to bridge the connection from the battery positive connection on the starter solenoid to the small screw where the red/blue wire was connected. The starter should crank the engine. If it does not, the starter solenoid is defective or the battery lacks sufficient charge to crank the engine.

If the starter does crank the engine, the problem is in the clutch safety circuit (5 speed) or Neutral Sense Switch (auto trans) or ignition switch.


See the Typical start circuit diagram above for wiring information for troubleshooting.

You will need a voltmeter or test lamp for the rest of the checks. Connect one lead of the voltmeter or test lamp to ground. The other lead will connect to the item under test.
Look for 12 volts on the white/pink wire when the ignition switch is turned to the Start position. Check the ignition switch first.
No 12 volts, replace the ignition switch.

The next step will require you to push the clutch pedal to the floor (5 speed) or put the transmission in neutral (auto trans) while the ignition switch is turned to the Start position.
Good 12 volts, check the clutch safety switch (5 speed) or Neutral Sense Switch (auto trans) for good 12 volts on both sides of the switches. No 12 volts on both sides of the switch and the switches are defective or out of adjustment. Check the wiring for bad connections while you are at it.
 

87fox72mach

Member
Nov 17, 2019
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pennsylvania
don't know if it makes a difference but I have negative battery cable ran from batter to a stud on the motor in front on passenger side. I notice the factory ground cable has a little splicede off of it that mounts to the body im guessing? would this be my issue?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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The smaller cable to fender apron has nothing to do with slow crank/no crank situation you have, it does need to be there for the computer ground.
 

jrichker

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makes sense. im gonna check all my grounds and possibly get new cables since mine r pretty old
Throwing parts, time. and money at a problem is a sure way to not fix the car, get poor and come to hate the car. Spending $20+ on a wild guess isn't a good plan. Do the checklist, it wall save you time and money!
 

87fox72mach

Member
Nov 17, 2019
8
1
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29
pennsylvania
I will do the checklist should I do it when the car has sat a while or when it has run and reached temp (this is when I have issues not when its cold from sitting) I know for sure my battery and terminals are good
 

87fox72mach

Member
Nov 17, 2019
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29
pennsylvania
ok finally got some time to tinker with the car today . I cleaned the 2 engine to body grounds I have, also the battery negative ground. and starter wire connection at solenoid.

with car off and cold I got 12.2 volts at battery after car ran a bit I got 12.7 volts at battery with car hot after a drive 12.2 volts. when cranking battery volts drop to 6.8 this was all a could do by myself gonna need some extra help with meter doing other tests with key on but car not running I got 11.6 volts between two posts on starter solenoid could I have a bad battery? I just got this one a few months ago any way something on my car is killing the battery life?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Take the battery back and have it load tested first, if you can charge it up some, also take the alternator and have it tested too. This is where I would start.
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
14,150
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polk county florida
Hit this linc to make sure it was done right, if done wrong it can cause a fire.
 

87fox72mach

Member
Nov 17, 2019
8
1
13
29
pennsylvania
so I decided to ditch the Taurus fan I had on and put the stocker back on problem solved no issues with starting the fan must be pulling too many amps I want to upgrade to a countour fan in the future I guess I will have to invest in a better fan controller as the one I have now is a cheapo