skyhigh4by

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82 truck with 87 motor, holley 670, .426/.450 113' cam, long tubes, heated o2, EGR disabled, painless harness, walbro gsl393 fuel pump, tune by tbichips.


I bought the motor second hand and swapped it in to my truck so I was kinda going into it blind to begin with. It has new CTS, map vacuum moved to front of TB, new o2, new 180 t-stat.

first the idle was high so I physically adjusted it down as much as I could but it was still about 900-1000rpm it would idle fine when warming up but once its warm it hunts from about 400-1000rpms. Its like a light switch once it gets to a certain temp it starts hunting.

I tried the procedure( jumping ALDL, let iac seat then unplug and start) to set base idle. With iac seated truck wouldn't even start without setting screw to open butterflies a bit. got idle to where it was happy (750-800rpm) but once it was warm it was hunting again (all with iac unplugged) once it go it to this point with it running but hunting I checked voltage on fps and it was 1.08v at idle. with adjustment screw backed all the way out the lowest reading I can get on tps is .87v the readings go up to about 4.5 nice and smooth. Haven't been able to find any vacuum leaks and TB base gaskets are new. iac seems to make quite a bit of noise with the ALDL jumpers in (grinding/buzzing)

Im sure Im leaving some things out but Im just a bit flustered and don't really know where to go from here. I just don't want it to almost die every time Im sitting at a stop light hahah

PS injectors dont leak and are spraying a nice cone/ fuel pressure is around 15psi

Thanks Ryan

RS-Chevy-SS

Are you checking the FP cold or when the surge is occurring? Check TB gasket as well, they sometimes get sucked out of place.

Ronny

iTrader: (1)

Have you considered increasing fuel pressure to see if it helps? Are you in closed loop at idle? If so what is the BLM read?

skyhigh4by

iTrader: (1)

Pretty sure TB gaskets are alright, they're new and i put a thin coat of silicone on them but I suppose I could pull it apart again. Im gonna search hard for vacuum leaks again today. I had fuel pressure gauge on it for quite a while it seems to be around 12ish cold and rises to about 15 once its warm.

I don't have a scan tool so I don't really know and unfortunately have no idea what BLM is. I feel like its not surging at all until its warm enough that it goes in to closed loop though. It gets to a certain temp then the idle drops down to where it should be when warm and begins hunting.

I haven't touched FPR. I know holley is adjustable but this one still has the brass plug intact. Also I had the TB off and everything about it and inside the intake looked spotless. Very minimal carbon build up anywhere.

skyhigh4by

iTrader: (1)

UPDATE:

this morning took it to local auto parts store to get carb cleaner to search for vacuum leaks again. drove normal on the way there but on the way back the idle wouldn't go below 1500rpm. got it home shut it off for a couple mins then fired it back up. idle stay way high. backed throttle stop screw all the way out and got idle down to about 800rpm. used a whole can of carb clean and couldn't find any vacuum leaks anywhere.

when you give the throttle a quick stab to about 1500rpm now it hangs for about 5 seconds then comes back down. no more surge

tps is at .92v at idle. now I'm gonna try to elongate holes in tps the get it down in the .5v area and see what happens.

Also it does seem to have a very slight intermittent miss and its running a bit rich(enough to pop code45) but no hesitation and seems to be lots of power

Im kinda lost and confused

Ronny

iTrader: (1)

I thought the Holley TBI system was to run at like 23lbs FP? Unlike GM at 12-13....

Another reason for a surge at idle is when the pulse width cannot get low enough(too much fuel or injector) and it goes from synch mode to asynch then back to synch in a rhythm....

skyhigh4by

iTrader: (1)

I spoke with a holley tech and he said it's supposed to run 11-12psi. I have read that the holley unit can be turned up to around 23psi but mine is at factory setting right now. Holley tech also told me that my pump may be pushing right through the regulator but then I read lots of info that said it wouldn't. By my testing the fuel pressure is a little higher than holley says it should be but no indications that it's pushing right through regulator and flooding out. Fuel spray seems pretty good. No drips either.

I was trying to set base idle again with iac seated and discovered that the surge seems to only be happening when the iac is unplugged. Also engine won't start with iac seated unless I adjust throttle stop open a bit. But once I set the idle then plug iac back in then I have to back idle screw out again because it's way to high once iac opens up. I'm still confused why TPS voltage is so high at idle though....

I disconnect battery to reset ECM each time I disconnect/connect a sensor.

Ronny

iTrader: (1)

I am not sure if this will help but if you were to leave the IAC connected yet plug the IAC air inlet you can possible rule out the IAC is the culprit. I used a foam ear plug. I did that years back when my IAC failed in a open position. I needed to open the butterflies a tad to get a warm idle. I have a manual trans so I could handle the cold engine initial startup. If idle is stable it must be the IAC or wiring to it.

skyhigh4by

iTrader: (1)

I put in a new IAC and so far it seems like that may have fixed it...

Seems to be running a little smoother and was able to set base idle. after i hooked it all back up the idle was still in the 700rpm range and very very slight surge.

still hangs for a few seconds when you stab the throttle though and it only does it when the IAC is connected and TPS voltage is .8-.9v range at idle...

Ronny

iTrader: (1)

That hang may be able to be tuned out. There is a filter that allows quicker movement/decay of its position reducing hang.

skyhigh4by

iTrader: (1)

Thanks. Im speaking with Tuned Performance to try to work on the tuning end of it.