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

Lee M. Lemoine llemoine
Wed Aug 16 06:26:44 UTC 2006

    It sounds like you've been down a long and windy road, and i'm half
awake and will comment more but the first things that come to mind are of
the EGR sort -- have you got the hole in the intake plenum blocked off?  On
my '93 Z24 i had to disable EGR out in the middle of nowhere, i simply took
the EGR valve off, RTV'd a quarter over the hole, and bolted it on finger
tight + 1/8 turn.   the whole intake plenum holds pressure (i pressure test
my turbo's intake setup from the plenum back through the intercooler,
straight into the turbo inlet!) so i know that that fix was air-tight.
   That'd be a pretty big vaccum leak and would cause your vaccum levels to
read funky, therefore causing you to have to tune the car a lot to make
things run "normal".    My other notataion was in the fluctuating TPS
value.  with the car 'idling' it should be steady, if its not check the
bolts holding the TPS, and check the wiring to make sure hte pins aren't
corroded.   If its still moving, try adjusting the TPS a little by loosening
the screws and 'wiggling' the sensor, and retightening -- sometimes it'll
get stuck at a value that keeps switching between percentages, and may dump
some extra fuel in as part of the throttle pump -- causing your lumpy idle.

I'd also suspect the popping to be caused by that too -- extra fuel burning
off in the exhaust and i'm sure thats driving your fuel trims up the wall
too.   Make sure the wirings good, and if it is, replace the TPS would be my
first thought -- i went nuts with mine programming the haltech on the
convertible -- best $23 i ever spent.

Good luck, and if i read this again when i'm awake, i'll give ya some more
to go on!
-- Lee

On 8/15/06, 93 Formula <red93formula at hotmail.com> wrote:
> 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 them.
> I have run VE-MAster 4 times on datamaster data with not enough change to
> make it go away yet.
> I see some things I don't like in the data but don't what to make of all
> of
> it.
> Also - could the egr effect anything?  I don't have one hooked up anymore.
> Should I turn something off or change the on/off values in the ecm? (I've
> 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 in
> gear or turn on the A/C...
> 2. When driving it - open or closed loop - from a stop to anywhere in the
> 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
> weird
> if using WOT
> I also noticed LT counts hanging around 108-114 range for a 9 second
> period
> 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
> even
> 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 few
> times)
> 1. I've helped the idle problem by adjusting the throttle stop out some to
> 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 feather
> 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
> it
> 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
> back
> 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
> the
> formula someone posted here a while back - I think its is like 31.xx as
> the
> constant.
> 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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Lee M. Lemoine
KB1NQI  - Amateur Radio
'06 Subaru Legacy GT Limited - 250/250 AWD 5EAT
'93 Chevy Cavalier Z24 Convertible - 300/330 FWD 5MT (Mclaren Turbo!)

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