M1088A1 Starting Issue

[BeetTrucker]

Hey guys, my m1088a1 will fire right up first start of the day but after it gets ran hard, cooled down and then shut down, if you try starting it right away it will not have anything at the start button. All dash lights will be on properly but there is nothing at all at the start button. Then, after it sits for an hour or so its fires right up as if nothing ever happened. Any thoughts on what could be causing this issue? Thanks!

 

[Suprman]

Maybe the starter going bad

 

[BeetTrucker]

Have a new starter ready to be thrown in, just odd that it will fire perfect first start of the day or when cooled down but not at all when the truck is warmed up.

 

[GeneralDisorder]

Sounds like a heat related electrical connection issue. How many grounds and starter connections have you cleaned? Have done a voltage drop test at the starter and aux solenoid while holding the start button? Any clicks from starter, aux solenoid, or PDP panel when you press the button?

 

[Ronmar]

No clicks at all with a button press? What relays are powered when you turn on the ignition?

What year is this truck?

 

[BeetTrucker]

Sounds like a heat related electrical connection issue. How many grounds and starter connections have you cleaned? Have done a voltage drop test at the starter and aux solenoid while holding the start button? Any clicks from starter, aux solenoid, or PDP panel when you press the button?

I put a new starter in, cleaned all wires and same thing. Have not done voltage drop as I haven’t had a second hand. When I flip the start switch to on I hear the clicks coming from the wheel well/solenoid/starter area but not from PDP panel. When I push the start button there are no clicks from anywhere.

 

[BeetTrucker]

No clicks at all with a button press? What relays are powered when you turn on the ignition?

What year is this truck?

I replaced the starter and cleaner wire ends with no luck. No clicks when push start button. LD2, LD3 and LD17 are lit up when switch is on start position.

 

[Ronmar]

Hmmm
well the no clicking is a significant clue. If it were a starter issue you should still get the aux start relay down on the drivers frame rail clicking when the button is pushed...

The LD's that are missing are the more significant clue. LD26/K26 neutral start and LD11/K11 alt excite must light/relays energize to enable the power to the start button. LD/k26 receives its power from the trans control unit. if your trans display is lighting up something is preventing it from giving a neutral start signal to energize k26. Are there any stored transmission codes?

Press up and down arrows together to enter diag mode and use the mode key to step thru memory location D1-D5, noting the 2 sets of numbers that flash for each D location IE: D1 25 35. it will repeat this sequence until you press mode to step to the next location or press the up/dn arrows again to exit diag mode...

 

[BeetTrucker]

Hmmm
well the no clicking is a significant clue. If it were a starter issue you should still get the aux start relay down on the drivers frame rail clicking when the button is pushed...

The LD's that are missing are the more significant clue. LD26/K26 neutral start and LD11/K11 alt excite must light/relays energize to enable the power to the start button. LD/k26 receives its power from the trans control unit. if your trans display is lighting up something is preventing it from giving a neutral start signal to energize k26. Are there any stored transmission codes?

Press up and down arrows together to enter diag mode and use the mode key to step thru memory location D1-D5, noting the 2 sets of numbers that flash for each D location IE: D1 25 35. it will repeat this sequence until you press mode to step to the next location or press the up/dn arrows again to exit diag mode...

Forgot to add, 2001 truck. As I said originally, if it sits it will fire right up, it is currently doing that. I can get it to start after it sits for a couple of minutes. I’ve now noticed that the alt/excite (k11) light is not lit up when it won’t start and it when it does light up, it will start. On my other 1088a1, k11 will light up with start switch but not k26 and it starts just fine. No codes were listed when going through diag mode.

 

[Ronmar]

K11 does double duty. when energized it provides power from CB77 to the start button. When it de-energizes it provides that same power to the alternator to energize it after start. K26 provides the power to K11s coil and the oil idiot light ckt provides the k11 path to ground. So as soon as you start and have 15 PSI of oil, K11 looses its ground and de-energizes which disables the starter and brings the alt online.

In order for k11 to energize k26 MUST provide its power. Perhaps LD26 is not working and k26 is actually energizing. With your hand on relay k26, you should be able to feel it click when the ignition sw is turned on. K26 provides power for k11 and that same voltage signal also goes to the ECU for neutral start input(probably wont allow the engine to fire if cranked without that neutral input from k26).

Do you get an oil pressure idiot light on the display panel at the same time k11 energizes when you turn on the ign? you should, as it is that same 15PSI switch circuit that allows k11 to energize...

 

[BeetTrucker]

K11 does double duty. when energized it provides power from CB77 to the start button. When it de-energizes it provides that same power to the alternator to energize it after start. K26 provides the power to K11s coil and the oil idiot light ckt provides the k11 path to ground. So as soon as you start and have 15 PSI of oil, K11 looses its ground and de-energizes which disables the starter and brings the alt online.

In order for k11 to energize k26 MUST provide its power. Perhaps LD26 is not working and k26 is actually energizing. With your hand on relay k26, you should be able to feel it click when the ignition sw is turned on. K26 provides power for k11 and that same voltage signal also goes to the ECU for neutral start input(probably wont allow the engine to fire if cranked without that neutral input from k26).

Do you get an oil pressure idiot light on the display panel at the same time k11 energizes when you turn on the ign? you should, as it is that same 15PSI switch circuit that allows k11 to energize...

It is intermittent, sometimes k26 will light up and sometimes it won’t same with k11. I just started it and K26 stayed on for close to a minute and k11 shut off quickly after start. When k11 and k26 aren’t turning on at key switch then the “engine oil pressure” light isn’t on which is a good indicator for me to know if it will or won’t start.

 

[Ronmar]

K26 should stay on till you shift out of neutral the transmission neutral signal controls its power and its ground is fixed.

K11 cannot come on unless K26 is on as k26 provides the power to k11...

K11 also cannot come on unless you have an oil pressure idiot light as the oil sw on the engine provides the ground for both the idiot light and K11 to energize.

So, no idiot light, no crank/start. idiot light and k11 should both de-energize shortly after start/15PSI oil.

This issue could be as simple as a bad oil pressure sw...

If k26 is indeed randomly coming and going while the trans still says N, could be a bad relay, bad wiring to the trans controller, failing trans controller or bad ground...

the grounds on these trucks are horrible, have you overhauled the ground strap connections? Power panel to cab, cab to passenger frame(behind grill) alt to frame, starter motor to frame...

 

[BeetTrucker]

K26 should stay on till you shift out of neutral the transmission neutral signal controls its power and its ground is fixed.

K11 cannot come on unless K26 is on as k26 provides the power to k11...

K11 also cannot come on unless you have an oil pressure idiot light as the oil sw on the engine provides the ground for both the idiot light and K11 to energize.

So, no idiot light, no crank/start. idiot light and k11 should both de-energize shortly after start/15PSI oil.

This issue could be as simple as a bad oil pressure sw...

If k26 is indeed randomly coming and going while the trans still says N, could be a bad relay, bad wiring to the trans controller, failing trans controller or bad ground...

the grounds on these trucks are horrible, have you overhauled the ground strap connections? Power panel to cab, cab to passenger frame(behind grill) alt to frame, starter motor to frame...

I have not cleaned up any of the grounds besides the one side of the strap connected to the starter. I will try cleaning the ends up on the grounds and seeing if that helps. But like said earlier, it seems like the longer it runs (hotter it gets) the longer it takes to get started. For example, I’ve started it and let it run for a minute or so and shut it off and it will take a minute or two to light up and start again. If it is ran for hours it has taken an hour to get started again.

 

[GeneralDisorder]

I would spend a week and clean every electrical connection and all the grounds. There's probably 100 of them that should be inspected and addressed. Not just from age - the manufacturer didn't really clean the paint well on many of them. I've seen a 2v drop between the cab and the frame on a 2 year old A1P2 armored cab truck built by Oshkosh in 2021. Especially the frame to engine grounds - both on the starter side and the ground strap to the alternator. The one's near the batteries, and ESPECIALLY the cab grounds - the one from the frame below the passenger cab pivot to the inside of the radiator tunnel and the one to the passenger grab handle under the PDP.

 

[Ronmar]

Well like I said above, what turns on or doesn't turn on with the ign on, when it wont start should point you right toward the issue...

oil idiot light: yes or no

k26: yes or no

k11: yes or no

 

[BeetTrucker]

Cleaned a few grounds but not all and have not resolved starting issue yet, but I can still go and I’m running it currently. New problem arose where CB67 and CB78 are now tripping and I’m losing my trailer brake lights and my cab running lights. I have headlights and all my interior lights still. What’s happening is K28 will click about once a second for about 20 seconds and then it will quit and trip both CB67 and CB78. Any ideas on this?

 

[Ronmar]

Relays clicking usually means current flow/voltage fluctuating issues. CB67 feeds all over the place via TB1. a prime place to look for marker issues however is where the wires pass into the doors to drive the door marker lights. common place to chafe and short to the chassis when the plastic wire protectors get damaged/removed...

 

[GeneralDisorder]

Did you inspect the main cab ground behind the grill yet?

There's really no point in troubleshooting weird behavior till you clean and inspect every connection. Then if you still have problems start doing voltage drop tests. These trucks were built with REALLY SHITTY ground and power connection implementations. When I worked for a manufacturer that did industrial wiring we had a wiring handbook with guidelines and requirements. IDK what the hell S&S, BAE, and Oshkosh are thinking with these trucks but their wiring practices are a joke.

And Ron's suggestion of the door markers is a good one. They deleted those on the A1R+ trucks. Too many problems. They deleted the door marker and the front cab marker and put a single 45 degree angled marker on the corner of the bumper. Less problems with wiring that doesn't have to route through a hinge point.

 

[BeetTrucker]

The lighting issue was a pinched wire on the cord going back to the trailer. Still dealing with this no k11 light/no oil pressure dummy light/no start Issue. Thinking about replacing the oil pressure sensor to see if that will fix my problem. Wondering which one is it in these pictures. The picture my hand is in seems like it’s the only one that the sensor Cat gave me will work for. The threads are smaller than the holes in the other two pictures.

 

[MatthewWBailey]

The lighting issue was a pinched wire on the cord going back to the trailer. Still dealing with this no k11 light/no oil pressure dummy light/no start Issue. Thinking about replacing the oil pressure sensor to see if that will fix my problem. Wondering which one is it in these pictures. The picture my hand is in seems like it’s the only one that the sensor Cat gave me will work for. The threads are smaller than the holes in the other two pictures.
View attachment 933988View attachment 933989View attachment 933990

That one you are pointing to is the atmospheric pressure sensor. The oil psi sender & switch are below the intake/Aih heater directly behind the PS pump.