Shoptalkforums.com

Hi all,
Iam back with more trouble, seems like this engine is going from badluck to badluck...

After changing the alternator and installing a new set of plugs because some did not fire a nice spark, i took the bus out for a quick ride.
Fuel up with super and took the highway, ran fine, took a small road to get to a campground (about 70 miles away from home and in another province) it started fumbling like it had no power when there was a load.

Stop in a parking, stop the engine, did a visual check, started the engine and it seemed ok, so i drove on to a narrow bridge where it died going a slight hill (worse place ever to be stuck....)

Someone pulled us to the campground and the next morning i checked the valves and plugs, it all seemed ok but it would not start (crank but nothing happens).

Got back home with the tow truck and now iam a poor fellow...


What i tested so far:
Checked the fuel pump , detach the out hose and had the fuel pump running in a glass container, plenty of pressure and the gas is nice.

Check the signal in tunerstudio and the cranktrigger is doing its job and i see the idle go up when cranking.

Checked one of the sparkplug and it does fire up nicely


So it has fuel and fire and the megasquirt seems to have the info it need but nothing happens at all when cranking.

My next test is to try after of the fuel regulator to see if the pressure and flow is ok. I will try that but after i dont know what to check.

Any taughts?

1971 bus
2276 engine
With a german fuel and wasted spark kit from the dubshop

Thanks everyone for your help.

Fuel tank vent system?

Fuel pump getting hot and delivering low/no pressure/flow?

Did you log anything during this drive, such as what was happening around the time of low power, and shutdown?

crank it for a while and try starting, then take the plugs out and see if they're wet?

Have to start with the basics, compression, fuel and spark.
Its easy to forget that its rarely the ecu, but either a basic mechanical issue or perhaps a bad sensor.

Now that you have it home, tho, you can use the ecu for diagnostics, make sure the cranking signal is good, tell the coil to fire 1000 times in test mode, test the injectors same way (pull the injector fuse) etc, see that the CHT or MAT sensor isn't reporting its -40 degrees... MAP sensor is reading as it should... Reload the tune to force a comparison or even reload the firmware if it looks like an electrical gremlin got it. (TS allows you to load any tune for comparison)

One time in a remote area on a cross country trip. I stopped for fuel as the next town was a long way off, was running on two or three by the time I got a few miles down the highway. Old, bad fuel glazed the plugs with varnish.
Had to (eventually) burn that fuel off via driving through it, refill the tank, and change the plugs several times, basically lost a day just keeping it running and recovering from that.

I was fortunate enough to have a small travel tool set and a couple sets of spare plugs to allow me to get through the issue.
It was over the christmas holidays, on the weekend and basically nothing was open, in the middle of nowhere, Utah in any case, >100 miles to the next town that might have an auto parts store for more new plugs and some drygas.

It took 3 days, 1000 miles and several tanks of fuel, many bottles of fuel system cleaner, as well as 4 sets of plugs before it was completely right again.

Good day,

About a month ago I was driving normally, then it died and didn't want to start. At the spot I checked everything I could with no luck and even called my wife to pick me up.

She brought me my DVM and everything great. When I was relaxed I look back at the ECU and saw the plug diagonal. I knew that was the issue even thou TS was connected to MS. I never screw those it bolts in on either side. I pushed it in and the car started and I was on my way.

It's always the simple thing that messes up a day.

Hope you find your issue pronto.

I would make a point to secure those connectors, DB connector pins/sockets are only rated for a few dozen cycles, and vibration would take them out pretty quick. Not doing so will lead to eventual flaky connections. Their use in an automotive environment is already arguably a bad idea, although few have had issues with them.

It's arguably OK to just use them as push ons in a non-moving non-vibrating installation like on your desk, but in a car its like teasing a bear.

MS1 or MS2 ? Do you have VREF. Does the FP prime and turn off? Do you have a stim?

What plugs do you have ? Through a "Fresh engine build" and tuning I have 3 sets of plugs to cycle through.
Base set : NGK BR7HS 1/2" reach. They fowled constantly while getting the tune better. No start condition when needing replacement.(frequent replacement). Swap the plugs out , Lights right up. I use baking soda blast to clean the fowled plug.

Blown fuses come from over current: a short ( I =E/R ) 12v/.5 ohm = 24 amps .5 ohm is a short

Be sure to check +12v and Injector and return for low resistance. That is 5 wires 1 + 12v and 4 returns depending on wiring style.
Mark

So i did a few more test and tried running the injectors in test mode but it did not work.
I looked at the relay box, injectors wires all tightly connected, checked the fuse and both were burnt...

I checked the wires (shielded) from the box to the injectors and did not see a trace of damaged to the shield or the wires. Replaced the fuses and still did not work. I look at the relay board more closely and found a path that seem burned or damaged but it goes from S4 to the main connector and S4 is a coil connection.

Now i dont get it... Is the relay board toast? Why would the coil work and not the injectors?




Thanks again everyone for your input!

Louis123,

My relay board didn't burn the traces but I wired the trace of the coil output from under the board to avoid any issues with the traces.