Big problems with new motor
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Joined: May 2001
Posts: 2,481
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From: Bloomingdale, IL , United States
Car: 1997 Z28
Engine: LS1
Transmission: T56
Axle/Gears: 3.42
Big problems with new motor
Hey guys, i need to vent a little and ask for a little advice.
Had 355 built by a local guy. The heads got a bowl job, headers, comp cam.
Well it is all back together, but i have a slew of issues i cant not figure out.
#1. I have crazy surge at idle, to the point where it dies in gear. I tried resetting my min air, but it made no difference. I suspected my iac, the iac counts are around 70. I have checked and double check for vacuum leaks, to no avail. Should i just try replacing my iac valve?( i did clean it)
#2. I can not for the life of me figure out why my oil presse gauge will not work. It worked with the 305, but will not work with the 355. I took it out and found oil in the plug area, so i replaced it with a delco unit, for whatever reason i have a third wire hanging of my sending unit plug(painless harness) could that need a ground or something? I have tried to get an answer from painless with no luck.
#3. It lacks power big time, i know it is need of a tune, we are currently taking baby steps in that direction. But when looking for my vacuum leak, i unplugged an injector to see if it made the idle worse, but everything seemed to remain the same. I would assume that uplugging an injector with the car running would get me some bad mis? Am i wrong there?
#4. This is the best one yet. I seem to be getting blue smoke on startup(heads were totally re-done) Is there any way to visually tell with the valve cover off what could be wrong, i assume it is a valve seal issue, which is strange, the motor has 100 miles on it since the rebuild.
I am getting fed up and need some help, thanks,.
Had 355 built by a local guy. The heads got a bowl job, headers, comp cam.
Well it is all back together, but i have a slew of issues i cant not figure out.
#1. I have crazy surge at idle, to the point where it dies in gear. I tried resetting my min air, but it made no difference. I suspected my iac, the iac counts are around 70. I have checked and double check for vacuum leaks, to no avail. Should i just try replacing my iac valve?( i did clean it)
#2. I can not for the life of me figure out why my oil presse gauge will not work. It worked with the 305, but will not work with the 355. I took it out and found oil in the plug area, so i replaced it with a delco unit, for whatever reason i have a third wire hanging of my sending unit plug(painless harness) could that need a ground or something? I have tried to get an answer from painless with no luck.
#3. It lacks power big time, i know it is need of a tune, we are currently taking baby steps in that direction. But when looking for my vacuum leak, i unplugged an injector to see if it made the idle worse, but everything seemed to remain the same. I would assume that uplugging an injector with the car running would get me some bad mis? Am i wrong there?
#4. This is the best one yet. I seem to be getting blue smoke on startup(heads were totally re-done) Is there any way to visually tell with the valve cover off what could be wrong, i assume it is a valve seal issue, which is strange, the motor has 100 miles on it since the rebuild.
I am getting fed up and need some help, thanks,.
Joined: Mar 2000
Posts: 1,692
Likes: 1
From: Corona
Car: 92 Form, 91 Z28, 89 GTA, 86 Z28
Engine: BP383 vortech, BP383, 5.7 TPI, LG4
Transmission: 4L60e, 700R4, 700R4..
Axle/Gears: 3.27, 2.73
A few questions:
Is the EST Bypass wire connected? It'll be the brown wire with the black stripe that you're supposed to disconnect to check timing. That can really keep the power down if you forget to reconnect it after setting the timing.
How big of a cam did you put in it?
Did you change injectors and burn a chip to run the 355 (basically MANDATORY for a speed density TPI)? If you're trying to run it with the stock chip, well, I'd start there. If it's on the stock computer, I'm surprised it's even running. The speed density computers (90-92 TPI) use the VE (@ MAP & RPM), and Cylinder size and Injector size to calculate the airflow into the engine, and then give what it thinks is the right amount of fuel. It has no direct measurement, other than it will try to achieve real 14.7 A/F when in closed loop by reading the O2 sensor and adding or subtracting fuel. This has a limit though, and can't "tune itself".
Do you have a way to scan the computer (not really for codes, (but start there), but to see what it says it thinks it's doing)? I have to recommend getting into PROM burning (which also involves some scanning software). You can pull the trouble codes without a scanner, your post count seems high, so I'll assume you know how.
A few comments:
The IAC is probably fine in your case. It's the computer that's controlling it, and it seems like it's moving. A bad IAC will move very little or not at all. A way to diagnose if it's probably working in your case would be to disconnect it and see if the surging changes. My guess is that the surging will change (any change, whether it surges more or less). That's not a full diagnosis of the IAC, but a quick reality check.
A V8 will idle surprisingly well on 5, 6, or 7 cylinders, especially on a new engine that has an unknown idle quality (cam), or when it's already showing other big problems. A better way to perform the cylinder drop test is to disconnect the IAC, rev the engine to about 1500 RPM manually, and then pull injector clips or plug wires. It should be easier to tell the difference there. If a cylinder doesn't drop with just the injector clip pulled, do the plug wire to diagnose if it could be a leaky injector.
I don't have anything on the oil pressure sending unit and blue smoke other than my best wishes. Hope it's just wiring, and unseated rings.
Is the EST Bypass wire connected? It'll be the brown wire with the black stripe that you're supposed to disconnect to check timing. That can really keep the power down if you forget to reconnect it after setting the timing.
How big of a cam did you put in it?
Did you change injectors and burn a chip to run the 355 (basically MANDATORY for a speed density TPI)? If you're trying to run it with the stock chip, well, I'd start there. If it's on the stock computer, I'm surprised it's even running. The speed density computers (90-92 TPI) use the VE (@ MAP & RPM), and Cylinder size and Injector size to calculate the airflow into the engine, and then give what it thinks is the right amount of fuel. It has no direct measurement, other than it will try to achieve real 14.7 A/F when in closed loop by reading the O2 sensor and adding or subtracting fuel. This has a limit though, and can't "tune itself".
Do you have a way to scan the computer (not really for codes, (but start there), but to see what it says it thinks it's doing)? I have to recommend getting into PROM burning (which also involves some scanning software). You can pull the trouble codes without a scanner, your post count seems high, so I'll assume you know how.
A few comments:
The IAC is probably fine in your case. It's the computer that's controlling it, and it seems like it's moving. A bad IAC will move very little or not at all. A way to diagnose if it's probably working in your case would be to disconnect it and see if the surging changes. My guess is that the surging will change (any change, whether it surges more or less). That's not a full diagnosis of the IAC, but a quick reality check.
A V8 will idle surprisingly well on 5, 6, or 7 cylinders, especially on a new engine that has an unknown idle quality (cam), or when it's already showing other big problems. A better way to perform the cylinder drop test is to disconnect the IAC, rev the engine to about 1500 RPM manually, and then pull injector clips or plug wires. It should be easier to tell the difference there. If a cylinder doesn't drop with just the injector clip pulled, do the plug wire to diagnose if it could be a leaky injector.
I don't have anything on the oil pressure sending unit and blue smoke other than my best wishes. Hope it's just wiring, and unseated rings.
Member
Joined: Dec 2000
Posts: 476
Likes: 0
From: sacramento,ca. usa
Car: 89 iroc,2012 eco 150,roadglide
Engine: zz4
Transmission: t56
the blue smoke on start up tells me a bad valve stem seal/bushing possibly.
computer will compensate for fuel change in disconnecting an injector.
computer regulates idle quality. have a new chip?
what are your tune specs?
base timing@6 deg. btdc.
iac counts at 70 sound o.k.
base idle @ 770 rpm w/iac disc.
tps @ .55
spark gap @45
fuel pressure at rail/idle 35-40 lbs.
computer will compensate for fuel change in disconnecting an injector.
computer regulates idle quality. have a new chip?
what are your tune specs?
base timing@6 deg. btdc.
iac counts at 70 sound o.k.
base idle @ 770 rpm w/iac disc.
tps @ .55
spark gap @45
fuel pressure at rail/idle 35-40 lbs.
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