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AFM744 AFM744 is offline
Cynical Misanthrope
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Join Date: Dec 2001
Location: Campbell, CA
Posts: 382
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Acceleration Enrichment Issue : SOLVED (?)

I've posted this twice on RL, so pardon me if you've already seen this.

I bought this '92 C2T w/ 86k and noticed this low-rpm stumble. Initial inspection revealed very loose intake manifold, so I tore out, cleaned up and reinstalled all the intake and fueling from the heads up. I still have a part-throttle acceleration stumble and lethargic throttle response at low rpms. And the wideband confirms, when I crack open the throttle it pegs the O2 at 16 for half a second.
Here's my first post for more info
For perspective, it idles on lambda, steady throttles on lambda, and WOTs at ~12.5 to redline so though I have not checked fuel pressures yet I'm not suspicious of them. I also cleaned, flow-tested and matched the injectors, so I'm satisfied with fuel supply.
I've narrowed down two possible sources;
-The WUR is not getting manifold pressure signal: so last night I ripped out the WUR and rebuilt it, doublechecked the throttlebody tap, and replaced all the vacuum plumbing. Started it up, still stumbles
-OR, the O2 Control Unit is not getting Throttle Switch part-throttle signals. While I had the manifold off last week I cleaned all the contact surfaces on the TPS. This does not confirm that the ECU/O2 Unit are actually receiving these signals though. I'm still favoring this suspicion b/c if I FLOOR it it enrichens fine, it's just the part throttle opening that it starves. The Control Unit is supposed to up the frequency valve whenever the throttle is opened, and again at 7d. The more I prod the accelerator from idle the more it stumbles, unless I floor it.
I don't have the Bentleys yet, so I don't have pin-out on the Controller Unit. How can you test/monitor the frequency valve activity? If anybody can offer TPS troubleshooting advice, or other input I'm all ears!
X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.

Last edited by AFM744; 10-26-2007 at 01:23 PM..
Old 10-25-2007, 11:52 AM
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