'95 Chevy 350 TBI rebuild woes

You need top recalibrate your ECM to run the bigger motor. It'll run like shit till you get a custom PROM burned.

Doc

.

yep.....yer correct.....it could be a number or things.

but..................

me, i wood ........

start with the fact that you didn't say one werd about the computer.......

or....... the service eng light.

00 L O

MarshMonster ~:~ =3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D '95 Chevy 350 TBI rebuild woes Group: alt.autos.4x4.chevy-trucks Date: Fri, Jul 9, 2004, 6:53pm (CDT-2) From: snipped-for-privacy@yahoo.com (odelrio)

I had to walk away because sometimes it's better to walk than to use a hammer. So first, the history. '95 Chevy Suburban with a 350 (5.7L) TBI seized when the oil cooler lines separated from the radiator and my wife didn't notice the gauges. So no problem, I needed a stronger motor anyway. I'd been eyeing this

383 kit from Powerhouse for my '69 camaro so why not put this torque monster to work in the 'burb... 4 weeks and several hours later, 383 is installed with an Edelbrock Performer manifold, cam, and TES headers to boot. Heads and TBI remained stock. So she's running... albeit a little rough. It sounded like it was missing and the new headers confirmed that cyl 8 was colder than the rest (no discoloring). Sure enough, spark plug was wet with anti-freeze. I didn't use RTV around the water jackets. Damn, my bad. =A0=A0New gaskets, gaskacynch, and black RTV and the leaks are gone. But she's still running rough. Checked #8 again and this time it's hot like the others. It could still be missing but I don't know. Maybe it's the cam, but I wouldn't expect that from the Edelbrock Performer. So rather than chase my tail, I checked timing. Timing is right at 0 degrees with the timing wire disconnected (bypass mode). With it connected, it's beyond the timing marks BTDC. I assume that's normal. =A0=A0What's interesting is that when I give it full throttle, timing drops below 0, maybe 2-4 degrees ATDC, it pops and then jumps back to high BTDC and revs nicely. Normal? Another data point is when I took it for a test drive. At half throttle it knocks pretty good. Hmmm, never did THAT before... ;-) And last, WOT, similar to that while playing with the timing, pop, accelerate, hesitate, pop, accelerate, hesitate, pop... Definitely never did THAT before. :-D So I'm thinking: o Maybe it's missing, it could be the plug wires (the plugs are new). o Knock sensor? o Perhaps timing needs to be remapped for the 383? o Too lean, bigger injectors? Not enough fuel pressure? In reading about the knock sensor it says not to use silicone sealers as it may isolate the sensor from the block. Well I used RTV on that bad boy because I didn't want it to leak. Interestingly enough, the Chilton manual says in order to remove, just unscrew it. So I thought maybe it doesn't hold anti-freeze and I used RTV for nothing. Went to remove it, anti-freeze everywhere. Plugged it back up and walked away...

I know there are possibly multiple things wrong here but I'm not really sure where to start. Ideas?

Thanks, Omar

Doc is on the money with recalibrating fuel/spark curves. Here is the problem......the 383 or most other SBC's need 32 degrees total advance @3500 rpm. The motor is popping because the plug is firing

2 degrees ATDC, the intake valve is already opening and drawing air/fuel into the chamber when the plug fires. POP and a flame out the intake sounds about right. 10 degrees BTDC will work at idle, but as the RPM's increase more advance is needed to compensate for piston speed and flame propagation. Everything is screwy with the TBI............ the MAP sensor is getting low vacuum with the cam so it thinks the engine is under a load and sends a inversely proportional signal to the ECU which in turn retards the timing and tries vainly to richen the fuel mixture............But wait there is more, the knock sensor is a very sensitive listening device and it's hearing all this racket going on with the popping and banging so it sends a high reference signwave to the ECU also telling it that massive amounts of preignition are taking place and we need to retard the timing even further to combat this problem. You would not to be in this ECU's shoes right now cause it's got more than it can deal with. sounds like a real challenge, wish i was there.....really

He can do that with either an OTC Genesis:

With the GM reprogramming module, or a Tech 2. The 95 has an E-PROM.

The parameters that need to be recalibrated will show on a scan immediately.

Just my devalued $0.02

Refinish King

PS He might have to go up about 3 Lbs. per hour on the injectors also, to compensate for the extra displacement.

Thanks guys. So what's the best way to do this? A quick search of OTC Genesys shows the GM Reprogrammer and Tech 2 to run at or above $1,000. Can this be done via component description to some place like Turbo City or do I need to take this in to a local Tuner? (Any you guys in sunny San Diego??? ;-) )

And last, how much should I expect to pay for this? A quick search here shows custom proms to be ~$350. Don't know what a Tuner would charge...

Thanks, Omar

I'd call jegs or summit racing

or and see if they have the ability to do it for you. If they can't, they'll sure as hell know who can. You should expect to pay between $150 and $350 for the ROM.

They'll need to know displacement (bore and stroke), compression ratio, cam specs (lift, duration i/e + lobe seperation), valve specs (size of combustion chamber, i/e valve size) and also what kind of exhaust you're running.

Doc

Doc

A new day, a new attitude...

In troubleshooting the potential miss, I started unplugging wires to see if the condition got worse or stayed the same. Interesting results, #2 has no effect. #3 got *better* (or rather smoother). All others were perceptibly worse (barely). A quick look at the firing order for a SBC, 1-8-4-3-6-5-7-2, and these two are opposed and exactly 360 degrees from each other. Hmmm...

I check the plug at #2, looked fine. Checked for spark, looked fine. Replaced the wire with a known good one, no difference. Checked compression, 190 lbs, again, looks good. WTF? I plan to check the intake valve, maybe it's not openning?

-Omar

PS Oh yes, and Mad Dog, I'd like to see any engine run if the intake starts openning at 2 degrees during the power stroke... It would have to be 360 degrees out of phase... Sorry, couldn't resist. ;-)

The 'puter you say? She still be a virgin 350 style. Didn't mess with it. And the check engine light is off though I know it works as it was on initially when I forgot to connect the vacuum line to the EGR valve.

-Omar

Odelrio stated: < What's interesting is that when I give it full throttle, timing drops below 0, maybe 2-4 degrees ATDC, it pops and then jumps back to high BTDC and revs nicely. Normal?>

Mad Dog stated:

Odelrio replied with:

Where did i say the intake valve is opening 2 degrees ATDC

PS Maybe you should read your own post and read my replies more carefully...sorry, could'nt resist ;-(

Mad Dog,

Didn't mean to offend. Too many beers on my part, I'm sure.

The way I understand a 4 cycle motor is Intake -> Compression -> Power

-> Exhaust and 180 degress separate each stroke. I believe TDC and spark timing is between Compression and Power. I apologize if my understanding is all screwed up. Probably why my motor's not working... :-D

-Omar

Have you given any thought to:

The distributor pick up coil?

Especially with the variable timing on acceleration.

Just a thought. Especially if it's an HEI type 3 distributor.

Refinish King

but..................

me, i wood start with the fact that you didn't say one werd about the computer,or the service eng light.

00 L O MarshMonster ~:~ ======== ======== snipped-for-privacy@yahoo.com (odelrio)

The 'puter you say?

She still be a virgin 350 style. Didn't mess with it.

And the check engine light is off though I know it works as it was on initially when I forgot to connect the vacuum line to the EGR valve.

-Omar ========== ==========

What "I" said wuz..... you didn't even mention it.

It's yer truck...do whut you want.

I stand by my original reply.

MarshMonster ~thinks yer a troll~ =============== ===============

Success! While removing all the *@#$%! plumbing in the way of the RH valve cover (and cursing GM for it), I finally got to the PCV hose (or boot) which attaches to the throttle body. The bottom side was cracked. Hmmm, says I. A possible vacuum leak??? Since I had already drained the coolant and removed the heater hose and the AC unit, I figured I'd re-adjust the valves anyways just in case. Two hours later and a new hose, she's purring nicely. No more miss, pinging or popping!

What a relief, I was going to go after the cam next!

Thanks for everyone's help!

-Omar

Thanks, I'll do that. I expected more power out of this 383. Now that it's running smooth, it feels very similar to what we had before with the 350. In addition to the longer stroke, I added the Edelbrock Performer manifold, cam and TES headers. This was supposed to give me primarily more torque but I would have thought noticeable HP too.

-Omar

It will kick some massive ass with the new PROM; right now the computer thinks you have a 350 and is delivering fuel and spark as such.

Doc

Yep, and it doesn't know about any cam that you may have there yet! 383 small blocks run very strong.

Brian