[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Low RPM roughness



> I recently completed a Jeep conversion, placing an 89 4.3 TBI & 700R4 into
a
> Jeep Cherokee.  I used a Howell Harness, a '7747 ECM, and stock 4.3 EPROM
> image (AKDX2088).  This engine was completely rebuilt, bored .030 over,
and
> I installed an Edlebrock Performer manifold, Edlebrock Performer CAM

(fairly mild roller cam, but definitely not stock),

Then the vac signal is different.  The ecm doesn't know other then what's
told, and how to respond.  Now that you've made the changes at the input
side of things, the outputs probably need tweaked.
  At the FTP is tuning.doc, and hunt around programming 101, and then check
back.
To get it reallly right now will take some research and learning on your
part
Bruce

>Edlebrock Roller timing chain,
> and roller rockers.  O2 is mounted on the Y-Pipe, just below the drivers
> side manifold collector (stock location on an S10 I believe...), and stock
> S10 manifolds were used.  Exhaust is 2.5 inch all the way back, with a
> high-flow cat and a FlowMaster muffler.
>
> After about 800 miles, the engine runs fairly good, but still has a few
> problems.  It idles very smooth, but does tend to hunt about 100 RPM when
it
> is warmed up to 195F.  It also runs very rough just off idle- anywhere
> between 750RPM and 1800RPM it just can't seem to keep from stumbling all
> over the place.  ECM never sets a code, and I have been having trouble
> getting stable ALDL data when the motor is running.  Timing is set to 6
> degrees BTC with the ECM control disconnected.  The ECM goes into
> Closed-Loop after 1-2 minutes after a cold start.
>
> Any idea what to look for when hunting this problem down?  Fuel Pressure
is
> dead nuts at 13PSI after I switched my fuel return line to a 3/8ths line.
I
> don't detect any vacuum leaks, but I wonder what the stock vacuum reading
> should be on this engine?  Again, it idles great aside from a minimal
hunt,
> but immediately off idle is where it starts to get unhappy.
>
> Also, this combo gets terrible mileage right now- I didn't expect good
> mileage, but I am running 14.5MPG right now, no matter how I drive it.  I
> have 4.55 gears, with 32 inch tires, with a corrected speedo gear- this
> 'appears' as something like a 4.11 ratio.
>
> I don't have the Edlebrock chip yet for this manifold/cam combo- so maybe
> that's the problem, but I would not expect to see it have problems at
these
> low RPM's.
>
> Any techies have a suggestion?
>
> --------------------------------------------------------------------------
--
> To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
> in the body of a message (not the subject) to majordomo@lists.diy-efi.org
>

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo@lists.diy-efi.org