y5e06

Hi all,

I recently did some work on my '4 Z camaro after it sat for a while. However, now it has a problem where it runs real poorly. There is a significant hesitation or miss below 3K rpms. If I down shift and run up the RPMs it actually runs smother and pulls fairly well.

My initial thoughts were that it was an emissions issue of some type, as I only *seemed* to notice it when it was hot. However, it takes me a while to get out of my neighborhood or onto the highway and its already warm by then. too much traffic around to trounce on the throttle all the time.

Here is a list of things I've replaced, obviously some of these are totally unrelated but I already have the list... note, the ones that say 'used '95 firebird' are ones I've swapped off my '95 'bird race car that ran fine to test the camaro parts.

Item source
oil pump- new Melling
timing set- new
O2 sensors- new AC Delco
opti- new GM
wires- new taylor
plugs- new NGK
valve springs- new LT4
intake gaskets- new felpro
water pump- new GM
hoses- new Goodyear
maf- used '95 firebird
IAT- used '95 firebird
intake bellows- used '95 firebird
map- used '95 firebird
egr solenoid- used & new, originial was bad
egr- cleaned
tps- used '95 firebird
PS Pump- new remain
PS hose- new
throttle body- used '95 firebird
iac- used '95 firebird
TB gasket- new felpro
plugged aux vacuum next to fp port at manifold
pvc port on TB plugged
fuel evap port on tb plugged
fp pressure idle- 39psi, 45psi unplugged
unplugged MAF- no change

edit:
fuel filter - new
ICM & coil unit - used '95 firebird


I recently cleaned the EGR valve as the most recent change. It was pretty carbon'ed up. but now I think it actually runs a tad worse. I've even disconnected the vacuum at teh egr and noticed no change. Idle even seems to have degraded, was fine before.

last time i checked my Freescan data, the O2's were cycling fine between .1-.9V,approximately. I didn't notice anything else w/ the software. however, i can't drive around and check teh data as my laptop battery won't charge.... so its garage monitoring only.

The drivability really feels like an old caprice I had where the opti was bad. misses and hesistates at low rpm. That was cured with new wires & opti. this one already has new wires and AC Delco opti. I could check the wires for the 3rd time, I'd even consider swapping out the new opti if they werent $500. Basically at my wits end.

.... at least the AC still works.

any solid ideas or insight (other than "I heard this could cause something similar, try it")

4K+Converter

A couple things just to check.

1) I'd yank all your spark plugs and check how much resistance each has with an ohmmeter. Sometimes they're bad right out of the box and will show significantly higher resistance than the others.

2) I didn't see anything about the coil or coil wire on your list. After doing heads and cam on my old LT1 car, it had a bad miss over 5K. Sometimes wires get old and brittle from heating up and cooling down inside their protective sheath and break up, especially after moving them around. I replaced mine and it improved and was only missing over 6K then. I figured out my Autozone coil wasn't up to the job of life over 6K, so I swapped in a MSD coil and it revved freely to 6.6K.

Edit 3) Fuel filter is another thing I'd replace just for grins. Cheap, and it can cause all sorts of problems when its clogged.

y5e06

oh yeah, sorry. those items you mentioned were swapped too.
fuel filter - new
ICM & coil (whole unit)- swapped from '95 firebird & spacers for heat added.

I plan on checking the plugs & swapping the wires this weekend. ordered a set of MSD streetfire (?) since its such a pain and no sense in swapping in the used wires I have when the MSDs are an affordable price.

tricked94camaro

iTrader: (1)

make sure you didnt crack the insulators on your plugs. have have bad experiences with NGK's and will never use them again

y5e06

I placed the wires with MSD's, just in case since I was there and it is a major pain. also pulled the plugs and inspected them. they all looked ok, including the porceline. maybe a tad on the lean side. rechecked the gaps. tightened up a few loose exhaust manifold bolts. put it all back together. swapped my original Camaro parts back on instead of the '95 firebird parts.

also, last time I cleaned the EGR pretty good. then when I drove it after that it actually felt worse. I pulled over, pulled the vacuum line off the EGR Valve and it seemed better. Based on the operating conditions where the poor running occured, I sure felt like an emissions related issue.
OK when cold, bad when hot, oK at WOT, and EGR behavior very suspicions.
since the EGR got WORSE after cleaning, I went ahead and got another from Autozone and swapped it on.

..... car felt great yesteday for a 10mile test drive! however, this morning on teh way to work I felt a couple instances of hesitation. so I'm still holding my breath. Its gotta be some quirky issue with the emissions.

Even though I function checked the EGR system thorougly and both seemed OK, both solenoid (replaced) and valve, it looks like it may be that system. If I continue to have minor problems I'm going to go ahead and make my own block off plates, delete the EGR, buy tuner CATS and tune it out of the engine.
the old valve really did seem to function OK. pulled open with ~5lbs vacuum, held the vacuum, and closed when vacuum released. even tried blowing through the valve and seemed to seal. checked the gasket etc too.
goes to show, even if it looks like a cat, smells like a cat, acts like a cat, but claims to be a dog, it is probably a cat.

side note:
at autozone had two EGRs listed
- federal emissions with auto trans
- cali emissions with auto trans
nothing available for manual trans. there was an entry for it but it was unavailable. I thought this was odd.
I knew my car came from cali and it is a T56. I went ahead and bough the federal auto trans version. I double checked gmpartsdirect.com and the auto & manual trans '94 were the same part number. No distinction or selection for california. so I went with the most common engine option, federal emissions automatic trans.
not sure what the differences would be except slightly different diaphram spring rates.

brucer

how bout knock sensor?

y5e06

doesn't look like it is knock sensor.
scan data shows zero change in knock counts and knock retard during a period where I experienced poor running while logging.

Here are a number of plots of data I captured. Red are points I highlighted as during the period where I observed the hesitation and sluggish response. this was about 45 up to 55mph in 5th gear. you can see the falling RPM and turn-on of TPS volts where I shifted from neutral & coasting to 5th & 'lugging' the engine as it runs from 1500 up to 2K rpm at just under 1/2 throttle.

TPS volts seem appropriate for the throttle inputs I was giving it.
O2 left and O2 right ranges were very similar, about what I would think are correct. .2-.9V
BLM Cell, you can see it locates in cell 14 during this run which is about right for rpm & MAP inputs.
BLM Left - I note it seems tuned to 131. from my reading, 160 is max. BLM Right was the same. so, OK given integrator oscillating appropriately or a tad too lean?
Integrator - I do not know. oscillating between 124 up to 136, depending on run time.
Pulse Width - do not know.
IAC - suprised it opens all the way up. however since I swapped Throttle Bodies I assume it is normal.
MAP - up to .95ish during part throttle. seems OK

Thoughts?
Is the BLM performance normal? IAC too?

y5e06

one more, spark timing. I find it interesting that it falls off to below 25deg adv and as low as 14deg adv. I suppose this is normal for <2K rpm and on partially on the throttle? when thinking back through my old carb'ed SBC days w/ vacuum advance it seems like it might be OK

y5e06

swapped fuel rail setup. no change.
injectors, fails, & FP regulator.

basically out of ideas & patience.

logged the drive home yesterday, about 16 mile trip.

noted that the most part, the BLMs were swinging well below 128. Indication of car running too rich all the time? haven't filled up yet, but the fuel guage seems to be dropping faster than expected....
L&R BLM are the same. Integrator (short term trim) oscillates around 128.