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Stutter at part throttle... Posted by Justin VanAbrahams [Email]  (#32) [Profile/Gallery]
(more from Justin VanAbrahams) on Mon, 8 Oct 2007 15:44:43
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i'm sure some of you have seen previous postings on my POS '92 900Tc. This thing is killing me - nothing I do makes it run right, and I'm pretty much at the point where it's 100% or parts...
Brief history: Bought the car in June of 2006 with a dead transmission - never drove it.
Upgrades: The head is a rebuilt (and fully tested) 2.1l head, 24# FoMoCo injectors, 3.0bar FPR, NGK BCP6ES plugs, Magencor wires, Bosch "Red" coil, K&N replacement insert, Magaflow 2.5" cat and 2.5" resonator (no muffler), custom upgraded APC (resistors, etc.)
Maintenance: Everything replaceable on the engine has been done - bushings, grommets, seals, vacuum hose. Distributor cap, rotor, fuel filter are all new. Fuel pump is new.
Other things I've tried: Good used FPR (pulled from my 5-door), Autolite platinum plugs, three AMMs, two AICs, another set of stock injectors, two distributors, and two ignition control units. I replaced all the plumbing from the turbo to the throttlebody, including the intercooler. I've replaced the wastegate actuator. The FI ECU was originally a -581 (IIRC) and is now a -948 (IIRC - the last generation 2.4 ECU)
Settings: TPS is adjusted, timing has been everywhere from 14 degrees to 18 degrees. Plugs were at .032, now they're at .028. Base boost has been everywhere from 4psi to 7psi.
Symptoms: Idles great, revs great. Put it in gear, pull away slowly, and as you get out of engine vacuum and through about 3psi, the car will as often as not stutter and lose power until you get more boost or more revs. If you are super-light on the throttle and never hit 0psi, you'd never know anything was wrong. If you floor the car there is a barely perceptible loss of power at 0-3psi, but that moment passes very quickly, and the car is at 15psi and flying.
It feels like a serious miss, or some sort of major vacuum leak. I installed a calibrated boost gauge, and you can see the loss of power, but then boost comes up and everything is fine. I installed a VDO voltmeter - alternator is charging at a very healthy 13.8v at all times. Mileage is good, tailpipe smells good, there is never a CEL.
The thing that is frustrating is that nothing I have done makes the problem go away or even affects it. It's intermittent, but always comes back. The only upside is that in dealing with the issue I've put a lot of upgrades on the car and now it's freaking fast... :)
I'm going to try installing an A:F meter and see if the O2 sensor picks anything up during these surges. Does anybody else have any thoughts? I've never had a car give me so much trouble...
posted by 207.15.18...
, Mon, 8 Oct 2007 15:44:43 <-- Viewing This Message, Wed, 10 Oct 2007 14:50:08, Mon, 8 Oct 2007 16:55:54, Mon, 8 Oct 2007 18:16:58, Mon, 8 Oct 2007 18:32:31, Tue, 9 Oct 2007 10:10:57
, Tue, 9 Oct 2007 15:28:37
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