Slow To Start After Running Around

[Zebvance]

My mj is getting harder and harder to start after it has been running around town. I'll turn it off, get in it a few mins later after I have ran in a store or somthing and it cranks and cranks and cranks, taking anywhere from 30 sec to a min of cranking to start. Any ideas? Is the starter just getting weak. Also it takes a few secs to start after it's been sitting over night also.

[Zebvance]

1988, 4.0, auto, 4x4 cps was replaced about 500 miles ago with a oem MOPAR one.

[ftpiercecracker1]

Is it actually turning over slow or turning over at a normal speed and just not firing?

 

Has it become progressively worse?

[Oyaji]

Is your compression good? As compression drops over the life of an engine, it will get progressively harder to start until finally it won't any more.

 

If compression is good, have a look over your fuel pressure. If pressure is slow to come up or if you have voids in the line, it will take longer for fuel pressure to build sufficiently, thus limiting flow through the injectors and causing long cranking time. A marginal fuel pump or check valve could be the cause.

 

As mentioned above, is the speed of the engine slow when cranking? Could be low supply voltage to the starter, or a starter on the way out. Low voltage to the starter will cause it to fail early - check your connections at battery and starter both.

[Zebvance]

I had the compression checked by a shop about a year ago for the head gasket. The told me there were no problems. That was less than 1000 miles ago. The fuel pressure regulator is new and the injectors but I haven't checked it with a guage. How do I go about doing that? I really hope it is not compression issue. The truck only has 105k on it. I will try to check the voltage on the starter soon.

[gogmorgo]

You can get a gauge that screws onto a valve on the fuel rail.

If this is the same MJ that recently had a starter switch/button installed, have you gone over all the connections to make sure they're good?

[Zebvance]

Yes it is. And this prob persisted before the install of the switch. I just now posted it. It always starts, just take a long long time of cranking before starting after running around in it for a while.

[91Pioneer]

It might not be your phone's fault. The site has been "hanging" on me when I click links for the last little bit.

[sloride]

O2 sensor been replaced lately?

[Zebvance]

Yes was replaced the same time the exhaust was. About 1500 miles ago.

[Eagle]

Check the resistance in your spark plug wires -- both cold and hot.

[Zebvance]

That and the voltage going to the starter are things I will be able to do tomorrow. So I will update then with that info

[Oyaji]

Again, if the starter is cranking the engine slowly, and if your battery is in good condition, your starter connection to ground could also be the problem. On problem starters for various engines over the years (including some big diesels in ag equipment that take 2 huge batteries to crank) I have run the battery ground to a mounting bolt of the starter, thereby offering the least resistance to the biggest power hog in the whole electrical system. Alternately you could check and possibly improve your ground connections: battery to ground, ground to engine, engine to starter. If that is no help, it's time to look at the condition of the starter.

 

A better description of the symptoms would maybe net you better advice - you got us guessing too much because you gave few details. ;) 

[Eagle]

That and the voltage going to the starter are things I will be able to do tomorrow. So I will update then with that info

 

Also check the amperage the starter draws when cranking. As starter motors age, the internal resistance can build up, resulting in slow cranking because the battery can't produce enough power. Somewhere in my tool box, from decades ago, I have a little tester that you just hold against the wire from the battery to the starter and it reads the draw by induction.

 

I don't think you have told us yet if the cranking speed is slower when hot.

[Zebvance]

 

That and the voltage going to the starter are things I will be able to do tomorrow. So I will update then with that info

 

Also check the amperage the starter draws when cranking. As starter motors age, the internal resistance can build up, resulting in slow cranking because the battery can't produce enough power. Somewhere in my tool box, from decades ago, I have a little tester that you just hold against the wire from the battery to the starter and it reads the draw by induction.

 

I don't think you have told us yet if the cranking speed is slower when hot.

 

I have not been able to test anything yet. I have been to busy with work and not had a second hand to help me test. However I was able to get some videos to better explain what it is doing.

 

 

 

 

This video is after It has been sitting over night

 

 

 

 

 

And this is after it has been running around town and it is at operating temps.

 

 

[xjrev10]

I'd change the CPS again. This time buy a middle of the pack price from rock auto or something. Install and see if anything changes. If not, you'll always have a spare CPS.

 

Swap your relays out with known good ones also..

[ComancheKid45]

Battery, Battery Cables, and possibly the starter.

 

Check ALL connections and the Battery/cables themselves. 

[Zebvance]

But I don't understand why is acts the way it does hot vs cold? If anything it would make more sense if it was acting the way it does with the situations reversed?

[91Pioneer]

Turn your phone sideways next time.

[Eagle]

But I don't understand why is acts the way it does hot vs cold? If anything it would make more sense if it was acting the way it does with the situations reversed?

 

Because heat increases the resistance in wires and connections.

[ComancheKid45]

 

But I don't understand why is acts the way it does hot vs cold? If anything it would make more sense if it was acting the way it does with the situations reversed?

 

Because heat increases the resistance in wires and connections.

 

 

Bingo

[jons87mj]

Could it be the coil?

[Oyaji]

Battery, Battery Cables, and possibly the starter.

 

Check ALL connections and the Battery/cables themselves. 

^^^ THIS.

.

 

But I don't understand why is acts the way it does hot vs cold? If anything it would make more sense if it was acting the way it does with the situations reversed?

 

Because heat increases the resistance in wires and connections.

 

Exactly.

 

Could also be that the starter isn't grounding well when hot, for exactly the same reason mentioned above. If not that, the starter could be on its way out - it is turning more slowly than it should even when cold. If so, brushes might be all it needs; you should be able to tell once you pull it apart.

[gogmorgo]

But check connections before pulling apart the starter.

[metrictonner]

I agree, you're getting a hot failure somewhere.  If you haven't cleaned your throttle body recently then your idle air stepper motor might be getting stuck closed in the warm gunk.  The motor can be ruined by forcing it to open while stuck.  Non-Renix models refer to this as an IAC.  Chysler parts refer to it as idle air bypass.