lightswitch triggers fuelpump/ecm

[Houseofperformance]

well, after years of ignorance i finaly got my sy up and running (or at least idling for now) on code 59, but now have an electrical gremlin wich i might get rid off easily with the help of people who actually know the wiring of these trucks..

when i turn the ignition on i get 2 sec fuelpump as planed - but when i turn on my lights (with ignition already on), i get them again, when i switch to highbeam too, when i hit the breaks and also when i use the turn signal...

i´m suspicious this is related to me performing the "4 hexbolt steering column tear down" last week to get rid of my steeringwheel wobble - but beside the horn wire i didn´t touch anything electrical in there - could i have disconnected/broken something down there triggering this behavior?

or is it more likley i fedup when wiring in the alky/wideband/code 59stuff, wich all work flawless and show no signs of my lacking talent concerning electrical connections

one last question: wich pin on the ecm is the switched 12v? so i can at least backtrack the problem when there is nothing obvious.

it would be great if somebody could give me a hint where to start searching - thanks

 

[Davemc1963]

Re: lightswitch triggers fuelpump/ecm

Sounds as though you have a ground problem somewhere.

Writing this from work atm, so it will be a bit brief. But as I recall, there is a ground behind the Dash panel, one at rear of drivers side cylinder head, one by thermostat housing, and one on the firewall. Then check the small ground wire from the battery to chassis. You can always run a temporary ground using a suitable wire with small crocodile clips on each end between suspect ground points. As long as the contact is good, it sometimes help locate them.

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

thanks - i checked, cleaned and tightend them already, nothing suspicious there.

but i´ll check again - maybe i just missed to hook up a ground, due to all the new stuff wired into the truck - but on the other hand - everything works as suposed to....

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

all grounds good and everything is grounded as it should be....

but still every single light relais activation triggers the fuel pump to prime for 2 sec as if the ecm would see switched 12+ for the first time...only when ignition already on, not when off.
could there be something wrong with the ignition switch or its wiring - i´m lost.

can the voltage drop in the system when a light relais ist activated make the ecm think it has lost its switched 12+?

 

[0966Sy]

Somebody install an aftermarket alarm and use the fuel pump wire for 12v ign? I'd start by looking at the wiring for the fuel pump and relay

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

thanks for the reply - no aftermarket alarm - fuelpumpwiring should be stock, fp test wire on firewall works too...

i suspect something wrong with the wire providing switched 12v to the ecm, but i don´t know wich pin it´s on to backtrack it.

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

thanks davep - i´ll check the wires tomorrow and report back...

completly rewired the battery (its under the bed) today, just to be save and rule it out - didn´t help my problem....

things i have installed before the problem ocured where the wideband, the alcycontrol system and the wiring of the wideband for code 59....

 

[sly dvl]

Re: lightswitch triggers fuelpump/ecm

I would think that if there was a poor B+ connection (that pulled the voltage down momentarily when the lights were turned on) there's no way you'd ever get the thing started, since the voltage would drop even more with a cranking engine. Sounds to me like something has shorted to power, somewhere within the lighting circuit.

Maybe start by unplugging the Alky and the WBO2 to see if they are somehow feeding back into the ECM, although I can't figure how either of those would ever be connected to a lighting circuit.

What happens if it's idling and you turn the lights on? Any glitch or hiccup in the idle?

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

ok - i checked the 2 red feedwires at the alternator - they have batt voltage and fuseble links are ok

i checked the load at ecm fuse 1 - no signifcant voltage drop when lights are on at the fuse - no sign. voltage drop at the pin a6 neither.

i installed extra ground straps - frame to coresup., core to intake, core to fender.

i´m running solid mounts, have the strap between head and firewall, headlight grounds are on the fenders on both sides....

only strange thing i found is a green wire exiting the drivers side headlight loom.....not hooked up - any clue where it belongs (i have abs, ac an cc removed)

when the car is running the problem isn´t noticeble - no hickup or anything.

 

[bezerk]

Re: lightswitch triggers fuelpump/ecm

I believe that green wire is for an extra horn?

 

[sly dvl]

Re: lightswitch triggers fuelpump/ecm

Wouldn't that "something" always be on if "shorted to power"? Particularly if it were a "light" in the "lighting circuit"?
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I would tend to agree, Dave. But, since we're dealing with semi-comductors within the ECM, perhaps the ECM isn't capable of feeding the lighting circuit, but the lighting circuit is certainly capable of feeding the ECM.

I know it's a really big stretch, but other than a short I can't see any connection between a lighting circuit and a fuel pump prime circuit. Unless (now that I think about it) the Fuel pump relay (control side) was finding a ground through the lighting circuit, and when the lights come on the relay is being back-fed? Meh, probably not...

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

thanks bezerk - might it even be the standard horn, since mine was never functional?

sly dvl - i pulled the alky fuse and unhooked the aem wb - no change

i start to feel the urge to ignore the fp/lightswitch problem, since it doesn´t seem to affect anything when the truck is running....but on the other hand i want to get things right before i actually start tuning.

i pretty much ruled out a groundproblem by now.....checked the switched 12v feed to ecm.....i have no clue what else could send a timed signal to the fp...

 

[sly dvl]

Re: lightswitch triggers fuelpump/ecm

Just curious, if you "tap' your brake lights with the Ign on, does the fuel pump run for a full 2 second prime, or just as long as the brake lights are tapped?

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

sly - wouldn´t the pump stay on full time if the relais would be triggerd directl? i definetly have a timed signal to the fp relais - fp stays on for 2 sec and goes out till i touch the lightswitch, hit the brake, turn signal.....again.

 

[sly dvl]

Re: lightswitch triggers fuelpump/ecm

You're right, if the lighting were feeding the relay directly it should be on all the time. That's why I asked about tapping the brake lights.

Alright, this changes my thinking slightly. Since the ECM is looking for a pulse from the distributor to run the fuel pump, it would appear that something in the lighting circuit is triggering the ECM into thinking that the engine is cranking (just for a split second) and the ECM responds by energizing the F/P relay. 1.75 seconds later the ECM doesn't see that phantom trigger anymore and it shuts off the relay, until the next event. If you repeatedly tap the brake lights, or left the turn signal on, does the F/P continue to run, and run, and run?

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

if i step on the brake fp goes on one time, no matter how long i stay on the brakes...if i hit it again - let off, and get on the brake fp is triggered again

different with turn signal, since it gets triggerd repeatetly...it runs till its shutoff time falls between 2 signals - then it stops and goes on with the next signal again...

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

sly, do you know at wich pin the pulse signal of the distr. enters the ecm?

since the switched 12 v to ecm seems to be alright, and the grounds too, the distr. pulse signal is something to focus on

 

[sly dvl]

Re: lightswitch triggers fuelpump/ecm

The only place the turn signal wires, the headlight & high beam wires, and the brake light circuits all come together is within the steering column. Having said that, I can't think of any ECM wiriing in the column except the Ign switch, and it's already on in order for all this to take place, so I'm really at a loss as to where the mystery lies exactly.

My suspicion is that when the lighting circuit is energized it's inducing a small amount of voltage into an adjacent wire leading into the ECM as a trigger signal. But I can't see for the life of me where these wires would even get close to one another.

Unless... do you happen to have an aftermarket tach mounted somewhere on the dash or column and the wires are running parallel to lighting wires in the column?

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

no tach - and nothing altered within the column wiring - BUT, i had the column teared down to tighten the 4 hex bolts....had to pull a bit on the cables to get them past the spline....maybe something disconnected?

will definetly check for the distr. pulse signal tomorrow....would a code 43 fit in this picture?

 

[Houseofperformance]

Re: lightswitch triggers fuelpump/ecm

thanks a lot for the help, if you have any othe ideas just let me know - will be hunting gremlins tomorrow again;-)