[Diy_efi] Hesitation, backfiring, jumpy blues :-(

Brendan Patten bpatten
Wed Aug 16 23:19:49 UTC 2006

Sounds like the case of a bad opti-spark distributor.  I had a 93 LT1 I
swapped into my truck, then sold to a friend.  Not too much later it
started exact symptoms you are describing.  Sometimes it would hardly
start.  He replace the distruibtor on it and it ran like a charm, at
least for about a year.  Then same thing.  Again, replaced distributor
and it fixed it.

The 93 was a non vented distributor.  Later models have a line that
draws intake air through the distributor and into the intake. Any
moisture build up can cause them to go bad.  Sometimes pulling the cap
and drying it out will help a lot, but not always.

Anyways, good luck, they are expensive, but most likely the cause.

Brendan Patten

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of 93 Formula
Sent: Tuesday, August 15, 2006 7:48 PM
To: fourth-gen at lists.f-body.org
Cc: diy_efi at diy-efi.org
Subject: [Diy_efi] Hesitation, backfiring, jumpy blues :-(

Anyone out there care to offer any other ideas of where to look for my 
problematic car?
Its been years and I haven't been able to drive it.
I have both diacom runs and datamaster runs.
If anyone wants to take a look, let me know and I'd be glad to email
I have run VE-MAster 4 times on datamaster data with not enough change
make it go away yet.
I see some things I don't like in the data but don't what to make of all
Also - could the egr effect anything?  I don't have one hooked up
Should I turn something off or change the on/off values in the ecm?
put this back to stock now)

Here are the symptoms -
1. Doesn't want to keep a "running" idle -aka wants to die when you put
gear or turn on the A/C...

2. When driving it - open or closed loop - from a stop to anywhere in
part throttle range, there is always like a jerk of the car like it
wants to 
die (I thought it was going lean) and then it surges forward

3. the rpm's seem to have the jitters looking at the data, the  LTs seem

wrong - not near 128 usually.

4. the only time it seems to run ok is when I mash it but even then 
something doesnt sound right.
  I also noticed that one LT was stuck at 130 instead of 128 - seemed
if using WOT
I also noticed LT counts hanging around 108-114 range for a 9 second
when I let my foot off the gas after a 10% TPS yikes.

5. popping in the exhaust - especially when letting of the throttle but
at part throttle driving this happens.

6. still starts hard - long crank and then wants to die for the first 10

seconds unless I keep in the gas - reminds me more of my 73 Charger
before I 
upgraded the ignition.

What I've done... (besides aging 30 years in 3)
changed programming like no tomorrow, went back to stock programming and

started over, tried VE master 4 times - Is this something you should
have to 
run a lot before it gets right?
chk'd or changed coil, coil wires, spark plugs - although that was a
year a 
go and they may be "fouled from too rich tests"  Would these really need

changing or would just a good hot romp burn em off? (which I've doe a

1. I've helped the idle problem by adjusting the throttle stop out some
raise the idle speed.
    I tried raising #s in the ecm but it didn't help.

2. usually the only way to keep it moving when it does this is to
the throttle until it finally gets going.

3-4. it does better to touch it at say 20% rather than a 5-10% throttle.
I noticed in the data that the tps changes even when I don't have my
foot on 
the throttle ???

I know there is some exhaust leak in the driverside Collector pipe since
never was a perfect fit
I don't know if that is enough to cause all of these problems though.
I did have problems with it starting and had to replace the battery - 
thought the pcm was dead, but apparently it was just my proms so I went
to my DOS program to make sure and it works but it
I run 30# f*rd injectors in it now and they are programmed according to
formula someone posted here a while back - I think its is like 31.xx as

Jeff  http://FindFastCars.com 93 Formula
Mods: 355 forged for NOS, LT4 HotTop, 58TB, SLP Cnvrtr, 3.73s, 
Mufflex/Spintech 4" exhaust, Hooker LTs, 300+ Ign, Injctrs, MSD Adj Win
Sw & 
3 Ign Ret, K&N CAI, Diacom, CATSTuner...

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