Vacuum leak detector...works well - The 1947 - Present Chevrolet & GMC Truck Message Board Network

weq92f · Today, 01:52 PM

.

So, been chasing a cold start idle and overall idle quality problem for a while now. I tried replacing and calibrating the IAC valve, adding a 1" spacer, mucking with physical blade adjustments and software parameter adjustment (AFR, idle target) to no avail.

Continuing this effort, I employed a pressurized smoke machine to look for vacuum leaks and disassembled my throttle body for inspection and cleaning. The cleaning didn't seem to do anything that I could make out as the unit is not too crusty but went through the steps anyway.

With the smoke tool, I found massive leaks on both sides at the rear of the mounting flange. Also noted smoke seeping from the very front of the flange. After some research, determined that my intake...Edelbrock 2161, is known to leak when using a square bore carb (my tbi is square bore). Edelbrock came out with a carb adapter plate (20 bucks) that makes this go away. I picked up the plate, installed it and now have no leaks.

The first cold start after this was 50% less bad and subsequent warm starts also seemed to be better. Overall idle quality is much improved. My suspicion is that with the vacuum leaks, the system was dumping more fuel and learned to continue doing so (fuel maps were richened up driving with the leaks). Now that the leaks are gone, I'm running rich. This should self adjust going forward and so I expect things to continue to improve.

Need to complete about 4 more cold starts and do some stop and go driving with more warm starts in order for it to adjust.

-Kevin

weq92f · Today, 01:56 PM

.

The throttle body. The thing has all this incorporated:

TPS
ECT
IAT
MAP
IAC
Fuel Pressure sensor
ECU

Fuel rail
4 80lb injectors

-Kevin

**Accelo** · Today, 01:56 PM

Good find. Back to basics before anything else.

weq92f · Today, 02:48 PM

.

Today's cold start didn't go perfect but it is a major improvement. Time and more learning will tell though...

https://youtu.be/z6jH39CdAfA?si=nV4qFVyoZa0NX5N_

-Kevin

54blackhornet · Today, 03:15 PM

And I thought a DualJet was difficult to tune ?

Today, 01:52 PM	#1
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 3,136	Vacuum leak detector...works well . So, been chasing a cold start idle and overall idle quality problem for a while now. I tried replacing and calibrating the IAC valve, adding a 1" spacer, mucking with physical blade adjustments and software parameter adjustment (AFR, idle target) to no avail. Continuing this effort, I employed a pressurized smoke machine to look for vacuum leaks and disassembled my throttle body for inspection and cleaning. The cleaning didn't seem to do anything that I could make out as the unit is not too crusty but went through the steps anyway. With the smoke tool, I found massive leaks on both sides at the rear of the mounting flange. Also noted smoke seeping from the very front of the flange. After some research, determined that my intake...Edelbrock 2161, is known to leak when using a square bore carb (my tbi is square bore). Edelbrock came out with a carb adapter plate (20 bucks) that makes this go away. I picked up the plate, installed it and now have no leaks. The first cold start after this was 50% less bad and subsequent warm starts also seemed to be better. Overall idle quality is much improved. My suspicion is that with the vacuum leaks, the system was dumping more fuel and learned to continue doing so (fuel maps were richened up driving with the leaks). Now that the leaks are gone, I'm running rich. This should self adjust going forward and so I expect things to continue to improve. Need to complete about 4 more cold starts and do some stop and go driving with more warm starts in order for it to adjust. -Kevin Attached Images __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

Today, 01:56 PM	#2
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 3,136	Re: Vacuum leak detector...works well . The throttle body. The thing has all this incorporated: TPS ECT IAT MAP IAC Fuel Pressure sensor ECU Fuel rail 4 80lb injectors -Kevin Attached Images __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

Today, 01:56 PM	#3
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,271	Re: Vacuum leak detector...works well Good find. Back to basics before anything else.

Today, 02:48 PM	#4
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 3,136	Re: Vacuum leak detector...works well . Today's cold start didn't go perfect but it is a major improvement. Time and more learning will tell though... https://youtu.be/z6jH39CdAfA?si=nV4qFVyoZa0NX5N_ -Kevin __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

Today, 03:15 PM	#5
54blackhornet Registered User Join Date: Jul 2008 Location: Eastern Oregon Posts: 2,367	Re: Vacuum leak detector...works well And I thought a DualJet was difficult to tune ? __________________ 71 C-20 07 Magnum RT AWD



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