Mep802a starts then shuts off

[kloppk]

Here is the path of the START signal from S1 to the K2 starter relay. There should be about 24 volts all along this path when S1 is in START.

S1-7------TB5-14------K12-8---K12-2-----K16-9---K16-6-------S7-1---S7-2-----TB5-20--------J6-20---P6-20-----K2-X2

 

[Guyfang]

Finally was able to spend some time troubleshooting. Followed the fail to crank all the way to step 11 of testing the reverse battery diode set. It says to test ohms of r10-r13 which should be between 7-7.8 ohms. R10 had 1.4, r11 had 2.4, r12 had 0.8, r13 had 0.8. R14,r15,cr1,cr2 were all correct. Ordered new resistors per troubleshooting and installed. Found after install that they all have the exact same readings. Decided to test the original resistors while not connected to any wires and found 7.5ohms. Any ideas on what could cause this? Where should I go from here? Tracing every wire is the only thing I can think of.

Everyone, makes this mistake at least once. But never again.

 

[rickf]

Checking resistors is a royal pain because you are going to be unsoldering and resoldering whether they are bad or not. At least then you know you don't have a bad solder joint at one of the resistors you took out to test and had to put back because it was good.

 

[Bassfishin114]

Checking resistors is a royal pain because you are going to be unsoldering and resoldering whether they are bad or not. At least then you know you don't have a bad solder joint at one of the resistors you took out to test and had to put back because it was good.

It never me mentioned in the troubleshooting about having to unsolder each one it is a pain. Well they are all good now but that was a wasted effort. Onto the next step.

 

[Bassfishin114]

Here is the path of the START signal from S1 to the K2 starter relay. There should be about 24 volts all along this path when S1 is in START.

S1-7------TB5-14------K12-8---K12-2-----K16-9---K16-6-------S7-1---S7-2-----TB5-20--------J6-20---P6-20-----K2-X2

thank you I will work on following this next weekend

 

[Guyfang]

It never me mentioned in the troubleshooting about having to unsolder each one it is a pain. Well they are all good now but that was a wasted effort. Onto the next step.

No. Not even. Not wasted effort. You learned something very important. Never test components that are integrated in a circuit. ALWAYS, unsolder one side. Then you can measure the component.

 

[Bassfishin114]

Here is the path of the START signal from S1 to the K2 starter relay. There should be about 24 volts all along this path when S1 is in START.

S1-7------TB5-14------K12-8---K12-2-----K16-9---K16-6-------S7-1---S7-2-----TB5-20--------J6-20---P6-20-----K2-X2

I followed the start signal and have signal up to k16-6. I have signal at k16-9 but not going across the relay. Tested the relay per troubleshooting and it tests fine. Ran a jumper across relay and I get crank but no start (progress). I switched multiple relays and still no change. Should I replace the relay holder then start troubleshooting crank no start?

 

[kloppk]

OK, K16 gets closed to enable cranking fron S14. The leftmost item in the row of relays. Be sure you can see a small circuit board inside S14 to be sure someone didn't plug a regular relay in there.
On S14 check for 24 volts DC across it's socket terminals 7 and 8 with S1 in Prime/Run. If you have power there then S14 is likely bad preventing K16 from closing and allowing cranking.

 

[Bassfishin114]

OK, K16 gets closed to enable cranking fron S14. The leftmost item in the row of relays. Be sure you can see a small circuit board inside S14 to be sure someone didn't plug a regular relay in there.
On S14 check for 24 volts DC across it's socket terminals 7 and 8 with S1 in Prime/Run. If you have power there then S14 is likely bad preventing K16 from closing and allowing cranking.

I had an extra relay that looked different with a circuit board in it so it looks like someone did put a regular relay in there. Put the correct one in s14. Measuring from terminal 7 to 8 i have battery voltage, measuring from ground to 7 I have voltage but nothing on 8 with s1 in run/prime. Followed troubleshoot for s14 and it says I should have nearly 0 volts on slot 1 while in run and I have battery voltage. Says to replace relay. They are sure proud of them over $100.

 

[loosegravel]

I had an extra relay that looked different with a circuit board in it so it looks like someone did put a regular relay in there. Put the correct one in s14. Measuring from terminal 7 to 8 i have battery voltage, measuring from ground to 7 I have voltage but nothing on 8 with s1 in run/prime. Followed troubleshoot for s14 and it says I should have nearly 0 volts on slot 1 while in run and I have battery voltage. Says to replace relay. They are sure proud of them over $100.

On the 802A’s and the 803A’s you are correct in your assessment that the left most “relay” isn’t actually a relay at all. I believe that it’s referred to as a “frequency trip switch.” I believe that it’s responsible for tripping faults for low fuel level, low oil pressure, high coolant temperature etc. I’ve picked up a few different units where the frequency trip switch was not in the correct position. The first time it happened, I lit off the machine and the frequency trip switched just smoked itself. I learned the hard way to check that they’re all in the correct position before attempting to start the unit!

 

[kloppk]

S14 the Frequency Trip Switch has nothing to do with faults. It does do two things. Enables and disables the starter to prevent the starter from grinding when the engine is running. S14 also enables and disable the Field Flashing function.

 

[loosegravel]

S14 the Frequency Trip Switch has nothing to do with faults. It does do two things. Enables and disables the starter to prevent the starter from grinding when the engine is running. S14 also enables and disable the Field Flashing function.

Thanks Kurt for that clarification!