Troubleshooting a running issue, TBI system.

American Delco GM ECUs and PCMs, ALDL, OBD 1.5.
ashhhhh
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Re: Troubleshooting a running issue, TBI system.

Post by ashhhhh »

Not on this unit, extending the IAC is the process used to set the minimum air - http://www.gmtuners.com/tech/TPS_IAC.htm
That link says 650 rpm so I figure 600 is pretty damn close.

If extending it stalled the vehicle then how would you set the minimum air.
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Re: Troubleshooting a running issue, TBI system.

Post by pman92 »

Everything you have done sounds good, but it still sounds like a leak of some sort.

Has it always done this? Or is this a new problem that has suddenly happened or slowly got worse?

Does it do it hot or cold or both?

I would be eliminating all possible vacuum leaks (do it again to double check).. Block the booster connection. Block PCV hose. If there's any vacuum hoses used for anything else block them. Keep only the MAP sensor hose.
See if that changes anything. I know you've done all this already but be 100% sure. If it ends up being a vac leak we can suggest things all day long but will never get anywhere.

When you free rev it while watching IAC count, when it initially drops to 1400rpm what are the IAC steps? Do you then see them come down as idle drops to where it should?

You mentioned it has EGR. Can you blank that off to make sure it's not leaking?
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ashhhhh
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Re: Troubleshooting a running issue, TBI system.

Post by ashhhhh »

Yeah its always done it. It was unregistered when I bought it so I didnt drive it prior to starting resto work. (which was body and suspension, not engine)
It does it hot or cold but its particularly slow to drop the revs off when cold. (when coming to a stop for example)

No worries, ill start plugging.
Ive got a spare evap canister with valve too, so ill try with that.

Off work crook at the moment so ill give an update on the weekend.
Ive attached a couple of charts which show idle and driving stats. Can add additional graph items if you want to see anything in particular.
Attachments
Cool driving.PNG
Cool idle rev behaviour..PNG
ashhhhh
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Re: Troubleshooting a running issue, TBI system.

Post by ashhhhh »

Theres a couple of vids too which show what I mean.
You can see in the "idle rev" one that the hang point actually increases if I stab the throttle before it drops right back.
The driving one is really slow speed obviously, but you can see what it does.
https://1drv.ms/f/s!AodQnnnWCBvbvGJFrM81DDSzOTRP
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Re: Troubleshooting a running issue, TBI system.

Post by antus »

I havnt looked at the vid but the graphs look ok. Which point in the graphs do you think looks wrong? Everywhere rpm is holding looks like the car is moving so its probably not triggering idle mode till under 5kph. I noticed similar on mine so i upped the idle kph to 20kph so it triggered when i hit the clutch rolling to a stop and i wanted the rpm to drop.
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ashhhhh
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Re: Troubleshooting a running issue, TBI system.

Post by ashhhhh »

No the charts look OK to me too but I know little about what it SHOULD look like.
Thats right, its holding revs when moving which makes it a total pain to drive, im waiting like 2+ seconds for it to be at the correct range for a smooth shift.

Yeah the video of the "driveway drive" is not great, its far worse one the road. Ill get the camera mounted and get a better example.
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