Final tune, Need help |
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Final tune, Need help |
Morph914 |
Mar 23 2022, 12:34 PM
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#1
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Member Group: Members Posts: 435 Joined: 22-August 16 From: St Augustine, FL Member No.: 20,326 Region Association: South East States |
Ok , so I have the engine running but it needs tuning. A little background, rebuilt stock 2.0 with D Jet, running a 123 dizzy. It fires right up and idles a little rough at first then smooths out. It revs fairly well and sounds good. The problem starts under load, it starts to stutter a bit.
I have not messed with the adjustment screw on the ECU or tried adjusting the throttle position sensor, or been able to check my fuel pressure. I’m hoping to rally any troops in the north Florida area to help me get these final details ironed out. Thanks in advance, John |
rhodyguy |
Apr 28 2022, 11:36 AM
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#2
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Chimp Sanctuary NW. Check it out. Group: Members Posts: 22,092 Joined: 2-March 03 From: Orion's Bell. The BELL! Member No.: 378 Region Association: Galt's Gulch |
I got stuck at the idle speed screw all the way in. Could an issue with the Throtte Body add to the problem?
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JamesM |
Apr 28 2022, 11:50 AM
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#3
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Senior Member Group: Members Posts: 1,915 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
I got stuck at the idle speed screw all the way in. Could an issue with the Throtte Body add to the problem? Anything is possible, but with d-jet a lot of issues share similar symptoms and more commonly people overlook things that you wouldnt immediately expect, like idle speed problems being related to a distributor, timing, fuel or PCV issue rather than an airflow issue. I have a ebay 2.0 TB in my parts stash that it appears someone tried to "fix" an issue by drilling a larger hole through the throttle plate and another one that it appears someone tried to "fix" by plugging the stock hole with a screw. So yeah, people seem to jump to the TB being an issue first but if your TB is unmolested its usually isnt a problem. |
JamesM |
Apr 28 2022, 01:04 PM
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#4
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Senior Member Group: Members Posts: 1,915 Joined: 6-April 06 From: Kearns, UT Member No.: 5,834 Region Association: Intermountain Region |
Here is something else worth pointing out that most dont usually consider, or that flys right over their head...
With a MAP (speed-density) based injection system (which d-jet is) changing your timing is also going to change your fueling under the same operating conditions, so when you are running your part/no load timing (vacuum advance/retard) outside of what was specified by the factory, d-jet is no longer delivering the proper amount of fuel for those operating conditions. Why? Because changing the ignition timing impacts the amount of vacuum that the engine produces and the amount of fuel a speed density based injection system delivers is based primarily on the vacuum it is sensing. Adding advance under part/no load from stock settings is generally going to generate more manifold vacuum. With a simple/analog/linear speed density system like d-jet the MPS sensing more vacuum tells the system to inject LESS fuel and while this can be compensated for when the throttle is in idle position by way of the idle mixture knob, as soon as the TPS comes off idle you are LEAN due to the increased vacuum from the advanced timing. Richer mixture and less advance are both things that will make throttle response feel more sluggish which is why people think they are improving things by jacking the advance BUT advancing timing and leaning fuel mixture (which happens by default when you advance timing with d-jet) are both good at increasing head temps. Meanwhile none of this makes ANY difference at WOT as at WOT there is zero manifold vacuum so you are timing solely off your RPM based advance curve. So your full throttle dyno runs are going to be exactly the same. So while it may feel different there are in reality ZERO POWER GAINS. Do you really think Porsche engineers left anything on the table with what they had to work with? Bottom line, to get the best running d-jet system possible EVERYTHING should be set to factory spec, including the distributor advance curve. Seriously think worn out distributors are responsible for far more injection/drivability issues than people realize. Yes gains can be had on a stock motor with a fully programable injection system, but d-jet isnt fully programmable, its fueling curve is fixed and already optimized for the motor. Taking anything out of spec with d-jet causes cascading issues. |
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