engine surges with 4 way flashers

[Mike Farquharson]

Hi when I put the 4 way flashers on at idle it is ok but  while under throttle  engine surges, any ides ? 

[Rikadoo]

How many rpm surge we talkin? 25, 100, 500? Does it do the same as lets say turning on the headlights? Or dash ac?

[Mike Farquharson]

the surge is about 500 rpm only does it with the flashers , ac does not affect it or the lights 

[Benjamin]

I love this kind of question!  Is your 8.3 a 12 valve with an inline bosch pump? or the 24 valve ISC with the CAPS pump?  Is the engine actually speeding up and slowing down with the flashers, or is it just the tachometer?

[Mike Farquharson]

8.3 12 valve inline pump and motor does go up and down ,     Thanks Mike

[Benjamin]

You got to be kidding me! I'm shocked the engine could actually rev and slow down that fast. The only thing on that engine that could possibly do this is the shut off solenoid, the cruise control, the alternator, or the transmission.  If there's no transmission codes, and the battery voltage is not also dancing along with the flashers, then I'm thinking cruise or shut off solenoid.  The cruise can be disabled by removing the wire, or shutting off the vacuum pump, to see if the surge goes away.  The shut off solenoid can be removed, and then pull up on the arm by hand to shut off the engine after testing. 

The only other thing I can think of are if you have any gas pedal linkage that's not mechanical, or if there is any cold start aid mounted on your intake manifold, like an ether start or flame start.  Those are all wacky land guess, but that's a wacky land problem.  Can't wait to hear what you find. 

[Rikadoo]

Well perhaps a 💩ground might, i find sooooo many bizar issues connected to a “poor ground” but i will say being a technition for the years i have been working on things is “ there finding new ways to fail”

[Bill R]

11 hours ago, Mike Farquharson said:

the surge is about 500 rpm only does it with the flashers , ac does not affect it or the lights 

Are you saying this happens while in D or N?  If in D, does the RPM surge happen while remaining in the same gear and the coach accelerates?  Or is the surge RPM a result of the transmission down shifting?  If it downshifts, does the coach then accelerate?

Edited June 24 by Bill R

[Ivan K]

I'd check around the throttle pedal wiring connector or if it has a grounding wire to same bar as the flasher that could have some issues. I would imagine the throttle wires go directly to ECM but maybe some sort of isolation damage. Since the idle is stable, it would be interesting if you had a way to see Throttle Position reading or at least engine power percentage.

[Benjamin]

12 valve 8.3 with an inline mechanical injection pump (I hope it's a cummins!), it won't have an ECM, external shut off solenoid only, any electronic or air throttle would be external just like a the vacuum cruise control this should have.

[Mike Farquharson]

have only tried the flashers in neutral will put it in drive and try it , Thanks Mike

[Benjamin]

While you're at it.  Leave it in neutral with the flashers on and engine revving, and take a look at the injection pump "throttle" shaft and shut off shaft to see if they are moving with the revving.

I'm assuming the engine is surging in time with the flashers, but you didn't say that.  What is the timing of the engine surges?

[klcdenver]

Since you have a smart wheel and that is how you can adjust the idle, maybe it is getting an erroneous signal thru it. Try canceling on the smart wheel and run the idle up and down using the buttons on the smart wheel. Just a wild guess.