TheSamba.com :: View topic - Fuel injection troubleshooting: Not sure where to go from here

Fri Mar 24, 2017 2:47 pm

I've gotten into this on other threads, here it is in a nutshell: Recently acquired 78 bus has never tried to start, except once when cold start valve was connected and I propped open the AFM. Then, it started and ran a few seconds at high RPM.

I changed out all the under car fuel lines and most of the engine compartment ones. After reading about engine fires being caused by the cold start, and mine seeming a bit loose, I removed the "T" sending fuel to it and unplugged it. Really want to know the engine is running on the injectors and not the cold start.

I checked all terminals on the double relay after straightening out some flakey wiring and have power at all terminals when it should be there. Fuel pump runs when key turned to start and when AFM vane opened. Tested and got strong spark from distributor. Compression sounds even between cylinders when cranked. Have voltage at FI connectors when key on and checked between terminal and ground- but not between two terminals when cranked (I'm using a 6-12v LED test light - there is enough voltage to light it, correct?) So it looks like I'm not getting pulses from ECU. I removed the plug and checked every terminal for either voltage or ground as described on a chart elsewhere in the forum. All tested out as they should. Opened the ECU cast to take a look, all looks as it should, nothing burnt.

Tested white wire from distributor to ECU, points to coil and ground wires on terminal under air plenum- all good. Engine still does not even try to fire. Not really sure how to proceed from here.

Fri Mar 24, 2017 3:17 pm

Pull the plugs and see how wet they are and do compression test.

Check to make sure all the injectors are firing-- real fuel- not just a click

Fri Mar 24, 2017 3:41 pm

Get a multi meter and test out the ecu plugs as per the fi troubleshooting manual.
How long has the engine been sitting, and are the injectors squirting gas or are they varnished shut?

Fri Mar 24, 2017 4:21 pm

If it will fire using the cold start injector, check for fuel pressure. 30 psi or so, then use a noid light to check for injector pulse. if you have fuel pressure and a pulse, it has to be the injectors. If the bus has sit for a while, the pintles in the injectors could be frozen.

These noids are available online, this one from Summit Racing for 5 bucks.

Fri Mar 24, 2017 5:15 pm

IT'S ALIVE!!! Turns out not to be a FI problem after all- I simply had the polarity reversed on the fuel pump. Corrected that, checked the fuel pressure and it pegged the tester (said over 100 lbs psi, this pump is supposed to be only capable of 72, maybe the tester is inaccurate?)

Plugged the fuel line back in and it cranked up in seconds, idled almost too slow and responds to the accelerator fine. Sounds like it is missing but that's OK, I can deal with that no problem Thanks to everyone who took the time to help me troubleshoot. Now on to the brakes!

Fri Mar 24, 2017 5:41 pm

mainstreetprod wrote: checked the fuel pressure and it pegged the tester (said over 100 lbs psi, this pump is supposed to be only capable of 72, maybe the tester is inaccurate?)
I sure hope so, L-jet runs 25-30 PSI, maybe 40 max. :shock:
Is that a Bosch pump?

Congratulations on getting it going, now do the safety stuff before planning any drives :wink:

Fri Mar 24, 2017 6:26 pm

busdaddy wrote: mainstreetprod wrote: checked the fuel pressure and it pegged the tester (said over 100 lbs psi, this pump is supposed to be only capable of 72, maybe the tester is inaccurate?)
I sure hope so, L-jet runs 25-30 PSI, maybe 40 max. :shock:
Is that a Bosch pump?

Can't tell for sure, someone has wrapped tape all over it, but looks identical to Bosch pumps of the era with the crimped end. However, instead of threaded terminals, they are male spade connectors, one normal size and one oversize. I guessed on the polarity and got it wrong.

Congratulations on getting it going, now do the safety stuff before planning any drives :wink:

Thanks! What safety stuff do you recommend other than fuel lines?

Fri Mar 24, 2017 6:53 pm

mainstreetprod wrote: Thanks! What safety stuff do you recommend other than fuel lines?
Well... from the umm... "creativity" we saw in your engine compartment I wouldn't trust any other system on that bus. I'd strip all 4 axles down to the backing plates or spindles and clean/measure/reuse or rebuild as needed, replacing all 4 rubber flex hoses would be a good idea as well. It doesn't matter how good it goes, if it can't stop it ain't worth a shit.
I'd also inspect the steering and tires closely.

And if they pulled that many hacks in the engine compartment I'll bet there's something special hiding up under the dash too, electrical fires and meltdowns really ruin your day.

Fri Mar 24, 2017 7:04 pm

busdaddy wrote: mainstreetprod wrote: Thanks! What safety stuff do you recommend other than fuel lines?
Well... from the umm... "creativity" we saw in your engine compartment I wouldn't trust any other system on that bus. I'd strip all 4 axles down to the backing plates or spindles and clean/measure/reuse or rebuild as needed, replacing all 4 rubber flex hoses would be a good idea as well. It doesn't matter how good it goes, if it can't stop it ain't worth a shit.
I'd also inspect the steering and tires closely.

No choice on the tires- they are easily the worst looking tires I've ever seen that still are holding air- cracking to pieces. So old they have no DOT designation to tell me the age (but probably somewhere in the 90's). Looks like the bus has been off the road for 20 or more years. The spare is bias ply and even older (but the rubber looks OK on it).

And if they pulled that many hacks in the engine compartment I'll bet there's something special hiding up under the dash too, electrical fires and meltdowns really ruin your day.

Under the dash looks OK other than the steering column ignition being replaced by a generic dash switch. All fuses in place and intact. I'll be going over the whole thing to be sure.

I'm really amazed this thing runs as good as it does, with all vacuum components disconnected except the advance.

Fri Mar 24, 2017 10:18 pm

mainstreetprod wrote:
I'm really amazed this thing runs as good as it does, with all vacuum components disconnected except the advance.[/b]

Your engine is running like ass. Reconnect all that stuff, It's there for a reason.

Sat Mar 25, 2017 6:43 am

FI needs no vacuum leaks for the mixture to be right. You said you replaced most of the fuel lines, you want to complete that task.
Flush the old brake fluid, inspect the pads and shoes, replace the soft lines, and make sure the parking brake functions.
Check the tires...are they rated for bus use? It's like driving on mush otherwise.
Grease front end, check steering components for wear, torn boots, CV boots too.

Mon Apr 17, 2017 1:24 pm

Okay, you say you reversed polarity on fuel pump .Was it pumping fuel with the terminals crossed ? reason I ask is I'm having a " No start " condition related to fuel .My early F.I. bus has gobs of new parts , is getting spark , fires when fed intraveniously . I had it running but idling poorly , then replaced afm meter with " NEW " hard to find not rebuilt unit .It is pumping fuel when the contacts on the double relay are manually connected { cover removed } or when afm flap moved . I believe I may ave a bad double relay or resistor pack , or perhaps totaly clogged injectors ? I tried to observe cold start and see if it delivered fuel , but it didnt . As I said fuel is pumping thru my lines , but not thru injectors , I had this thing running fairly strong ...Anyone care to help
p.s. someone said there were two folks that clean /repair injectors tat come highly recommended ,anyone know their names , and also Colin ,if you read this wats your western itinerary look like for some Elk steaks in Wyoming and a Mountain Bus rescue. SUMB...

Tue Apr 18, 2017 2:38 pm

VeeDubb steppin wrote: Okay, you say you reversed polarity on fuel pump .Was it pumping fuel with the terminals crossed ?

No, terminals being crossed was trying to pump backward (DC motor).

reason I ask is I'm having a " No start " condition related to fuel .My early F.I. bus has gobs of new parts , is getting spark , fires when fed intraveniously . I had it running but idling poorly , then replaced afm meter with " NEW " hard to find not rebuilt unit .It is pumping fuel when the contacts on the double relay are manually connected { cover removed } or when afm flap moved . I believe I may ave a bad double relay or resistor pack , or perhaps totaly clogged injectors ? I tried to observe cold start and see if it delivered fuel , but it didnt . As I said fuel is pumping thru my lines , but not thru injectors , I had this thing running fairly strong ...Anyone care to help
p.s. someone said there were two folks that clean /repair injectors tat come highly recommended ,anyone know their names , and also Colin ,if you read this wats your western itinerary look like for some Elk steaks in Wyoming and a Mountain Bus rescue. SUMB...

Remember that all 4 injectors are unlikely to fail at once. Something as simple as losing the ground to your ECU at that little 3 way grounding tab under the air plenum can stop the injectors cold (or ECU failure, much less likely).Also, make SURE the ECM plug is on good. Even if no injectors are injecting, your bus should still start and run a few seconds when the cold start feeds it fuel.

I believe if you move the AFM and get fuel you have a working double relay.

Tue Apr 18, 2017 2:48 pm

It's worth your time too, from the ECU plug all the way to the double relay to not only remove and clean all the connections to assure no corrosion has gotten between them, but also look into each plug to make sure none of the wires have slipped back into the plug and aren't making contact when the plug is attached. Especially all the wires on the left connection at the double relay

Tue Apr 18, 2017 6:00 pm

I've been wondering what your spark plugs look like. They should tell you if it's isolated to a cylinder or two or none... Years ago I had an issue where if wasn't running quite right. Plugs 1, 3 and 4 were normal, 2 was black. Turned out my FI connector was so buggered up it wasn't firing. $12 injector connector later was running great. Maybe not your end all fix but worth checking.

I'm also wondering if you've plugged in the rest of the FI components? I'm surprised the bus even starts with so many missing parts.

Good luck!

Tue Apr 18, 2017 8:49 pm

Thanxz to everyone for taking time to respond , This Bus has a complete brand new " Kyles " awesome engine harness , new fuel pump , cleaned tank ,new filter and lines .No fuel was coming thru cold start , I know the cold start can go into a non work mode , under certain circumstances . Im betting on a ground gremlin or /wire connector ,or bad 2xrelay. This bus arrived as a basket case , I got her running , and have proceeded to clean ,retrofit , and fall in love with the Lil Fraulien , My Bavarian Bombshell...miss Lily Von Schtuup...

Tue Apr 18, 2017 9:04 pm

VeeDubb steppin wrote: Thanxz to everyone for taking time to respond , This Bus has a complete brand new " Kyles " awesome engine harness , new fuel pump , cleaned tank ,new filter and lines .No fuel was coming thru cold start , I know the cold start can go into a non work mode , under certain circumstances . Im betting on a ground gremlin or /wire connector ,or bad 2xrelay. This bus arrived as a basket case , I got her running , and have proceeded to clean ,retrofit , and fall in love with the Lil Fraulien , My Bavarian Bombshell...miss Lily Von Schtuup...

Remember that the CSV only runs when starting the bus. Unplug the connector to the CSV and check that you're getting ~12V while you turn the key to start it. If not, check the connection to the TTS under the plenum, check the grounds on top of the engine block, check connections on left side of the double relay, give double relay a few taps with a rubber mallet.

Tue Apr 18, 2017 9:32 pm

_________________
I need to hook a remote start switch , I have not been able to check voltage while cranking . I have juice at te resistor pack , at injector terminals when ignition is on . .I have juice at 88y, 88z,88a,88b,86c as well. It fires rite up with a shot of fuel in the cold start port hole . If the termo time were bad will that absolutely keep it from firing cold , or just make it difficult ? I tried 3 spare 2x relays , none ever verified as working however !

Tue Apr 18, 2017 10:12 pm

If the CSV isn't properly connected to the TTS it won't be grounded. You need to verify power at 86a/86 on the left side of the double relay while cranking. That circuit is powered via the starter terminal 50 while cranking. Should be a red and white striped wire.

Tue Apr 18, 2017 11:07 pm

Roger that ! I need eiter 1.] a warm body to engage starter , or 2.] a remote starter hooked up . Right now I have neither .This Bus is right there, wanting to start , but there may be an Ah HA ! moment in my future ...hopefully . I'm going to go back and triple check my connections etc , while I wait for a 2xrelay .