Throttle Response Problems

[Walter Petermann]

ABTSZ wrote:
> 
> Hi all,
> 
> I acquired a fuel-injection sytem from an '88 Chevy Berreta 2.8 V6 (730 MAP
> based system), and I put it on my Jag 4.2 straight six, using a manifold and
> throttlebody from a later fuel injected Jag.  The injectors are 24# Ford SVO
> (the original jag injectors were 20# low impedence, and not large enough for
> my modified engine.)
> I eliminated everything from the harness except the MAP, TPS, water temp, air
> temp, knock sensor, and DIS.  I have the P\N wire grounded.
> The car runs pretty well, EXCEPT for the throttle response.  The throttle
> response is so bad, that from a stop, the car will stall when I step on the
> gas unless I press the gas pedal as softly and slowly as I possibly can.  Even
> then the car stumbles rather severely before taking off.  The throttle
> response is pretty poor, even at speeds up to about 60 MPH.   The car
> accelerates smoothly once it gets going.  Idle is pretty good, too.  WOT is a
> little rich, but thats not too bad, actually!
> I have checked out the TPS, since I would imagine this is where the problem
> would originate, but everything seems to be OK.  I get no error codes, and I
> have the TPS set to about .65 volts at idle (the manual states .45 to .85 V at
> closed throttle) and it goes up to about 4.5v at full throttle.  I have tried
> adjusting TPS in different positions, all the way up to 1.1V at idle, with the
> best results at higher voltages, but still unacceptable throttle response.
> The only thing I can think of is that the Jag throttle plate is SO MUCH larger
> than the Chevy (about 65mm vs. @ 45mm? (I didn't measure, but its a BIG
> difference.))  I think this might result in a much larger amount of air
> rushing in at small throttle openings.  But then the engine is much larger,
> also.  So ratios might be the same, and that is what counts.
> Has anybody else had similar problems?  Does anybody have any ideas as to what
> could be causing this or any suggestions or work arounds?
> ANY suggestions would be welcome. This seems to be the only (however severe)
> problem with this system so far.  I have excellent idle, acceleration, milage,
> etc.  But the throttle response problem makes the car almost un-drivable in
> traffic (and maybe even a little dangerous!)
> 
> TIA,
> Adam
> 
> PS I even checked the Harness for continuity, and there are no problems there.

To test yout throttle pot you might try taking it off the
throttle body and operating it manually with the car at
idle. If you don't get any change in rpm while turning it by
hand...

If it does turn out that it's working, you might try to move
the map sensor vacuum hose closer to the throttle plate, if
that's possible.

 Walter