Help - Engine redlining without throttle input

lucmor444 · Postby **lucmor444** » Thu Sep 22, 2022 7:30 pm

Today my NA8 suddenly revved out to redline with any throttle input and will not reduce revs. Shut it down and start it up again and the problem remains.

Throttle cable etc all working fine.

Tomorrow I'll check all vacuum hoses but on quick visual inspection nothing broken, loose etc.

I'm on Jenvey ITBs with a Megasquirt (Alex Barton has advised it would not be a problem with the ECU).

As I start to tackle this problem is there any other things I should be looking at?

StanTheMan · Postby **StanTheMan** » Thu Sep 22, 2022 7:33 pm

who is Alex Barton? and which ECU are you talking about.

with ITB's you don't have a idle valve . right?

lucmor444 · Postby **lucmor444** » Thu Sep 22, 2022 7:44 pm

Alex Barton AKA 'Bartmanftw'

Running a Megasquirt and I don't have an idle valve.

StanTheMan · Postby **StanTheMan** » Thu Sep 22, 2022 7:48 pm

which mega squirt?

lucmor444 · Postby **lucmor444** » Thu Sep 22, 2022 7:49 pm

Sorry - Megaquirt2

StanTheMan · Postby **StanTheMan** » Thu Sep 22, 2022 8:02 pm

iM unable to be of help. sorry
when this has happened to me it was about the Idle valve , connection to it and setting of it. on an MS2

What Bart probably means is that the MS2 is working ok but something has happened to make the ECU rev the ƒü¢k out of it.

lucmor444 · Postby **lucmor444** » Thu Sep 22, 2022 8:07 pm

Thanks for the effort anyway StantheMan.

greenMachine · Postby **greenMachine** » Thu Sep 22, 2022 10:50 pm

If the throttle plates are closed, how on earth can it run to the redline? Where is the air getting to the inlet valve?

:mrgreen:

lucmor444 · Postby **lucmor444** » Thu Sep 22, 2022 11:49 pm

I don't know the answer to that Greenmachine. Diagnosing engine problems is not my forte:(

greenMachine · Postby **greenMachine** » Fri Sep 23, 2022 12:07 am

Is there a disconnect somehow between the pully on the throttle cable and the throttle shaft, so that the throttle plates can move independent of the throttle cable? Loose pulley? Broken shaft? That is, the pully may be in the closed position, but are the throttle plates closed also? See if they move (rotate) without moving the cable pully.

To rev to the limiter it needs fuel and air, and if the throttle is closed (apparently) it has to be getting it from somewhere...

What were you doing when this first happened, any chance that might have upset something?

Very strange, but I'll bet there is a simple answer, even if it is not simply found ...

:mrgreen:

93_Clubman · Postby **93_Clubman** » Fri Sep 23, 2022 12:45 pm

lucmor444 wrote:Throttle cable etc all working fine.

My thoughts are similar to GM - appreciate you say the throttle cable appears to be working correctly, but were the throttle plates actually closed when it redlined? Have you or anyone else recently done any work on the vehicle? Is there some sort of cold start arrangement with the Jenvey ITBs & MS2? As GM says to redline it needs fuel & air, so it's getting it from somewhere.

bruce · Postby **bruce** » Fri Sep 23, 2022 2:10 pm

You'd think it would be something obvious like a disconnected hose, etc.
Are u sure the cable is connected and the actual throttle is stuck open (which it must)?

lucmor444 · Postby **lucmor444** » Fri Sep 23, 2022 6:35 pm

Thx for the further inputs.

The throttle cable is definitely all OK and correctly operates at least the one throttle plate inspected (albeit I'll be checking all 4 throttle bodies on the weekend and check what happens when the engine is 'running').

Also tomorrow I'll check the vacuum hose running to the MS2.

No new work has been undertaken on the car. The only concern I have was during lockdown the car sat with a tank near empty.

I'll update if I make any progress.

StanTheMan · Postby **StanTheMan** » Fri Sep 23, 2022 6:47 pm

tank near empty ? nahhh it would;d starve of fuel of anything if there werre any deposits in there

seems you have plenty of flow . LOL

rascal · Postby **rascal** » Fri Sep 23, 2022 8:08 pm

lucmor444 wrote:Thx for the further inputs.

The throttle cable is definitely all OK and correctly operates at least the one throttle plate inspected (albeit I'll be checking all 4 throttle bodies on the weekend and check what happens when the engine is 'running').

I’d hazard that either the linkage has come loose for the other throttles, and the one you checked is the only one working, with the others are fully open, or you have a pretty sizable vacuum leak somewhere. Something like the manifold has come loose from the head or something silly like that. Normally a vacuum hose leak just gives a highish idle, not redline material…