LT1 breaking up at high RPMs - advice needed
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Teching In
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LT1 breaking up at high RPMs - advice needed I posted this as a reply to another thread, so my apologies for the double post:
My buddy has Firebird former V6 car that we put a '97 LT1 into. The motor starts breaking up at around 5500 rpm... kinda like it has hit a rev limiter. Sometimes it will power through, sometimes it won't. The revs drop so I don't think it is the trans slipping.
The motor has 34K on it, and we put a new optispark and MSD wires on it when we put it in. The heads were never off, but everything else was apart and it looked good. It has broke up at high RPMs since day one. Here are the new parts since:
Plugs
Coil
Wiring Harness
MAF
Injectors
Fuel Pump
Valve lash adjustment
Still does it. Could it be a bad Opti from GM? Would the MSD cap and rotor help? We are lost and my buddy is getting sick of throwing money at the car.
Mods are:
LT Headers
LT4 Hot cam
1.6 RRs
exhaust
cold air intake
Ed Wright tune
We have since taken it to Speed Inc for some dyno time and a better tune but it was breaking up so bad Jim couldn't get a good baseline pass.
Please help, we are at wit's end.
-Aaron
My buddy has Firebird former V6 car that we put a '97 LT1 into. The motor starts breaking up at around 5500 rpm... kinda like it has hit a rev limiter. Sometimes it will power through, sometimes it won't. The revs drop so I don't think it is the trans slipping.
The motor has 34K on it, and we put a new optispark and MSD wires on it when we put it in. The heads were never off, but everything else was apart and it looked good. It has broke up at high RPMs since day one. Here are the new parts since:
Plugs
Coil
Wiring Harness
MAF
Injectors
Fuel Pump
Valve lash adjustment
Still does it. Could it be a bad Opti from GM? Would the MSD cap and rotor help? We are lost and my buddy is getting sick of throwing money at the car.
Mods are:
LT Headers
LT4 Hot cam
1.6 RRs
exhaust
cold air intake
Ed Wright tune
We have since taken it to Speed Inc for some dyno time and a better tune but it was breaking up so bad Jim couldn't get a good baseline pass.
Please help, we are at wit's end.
-Aaron
Same problem here except I have a Delteq distributorless ignition. I thought it was supposed to eliminate the opti problems! I have three theories so far. My advance above 5000 is too high. I have a friend who is a gearhead from way back. He said I should be seeing about 38 advance that high up, not 44 or so like I have. I need to test that. My optical is bad. However, I have conflicting advice. Some say if it free revs past 5000 the optical is fine and is not load dependent. Some say it can cause a bad signal if it isn't perfect. It's the Delteq coils. Perhaps they're bad but I'm inclined to think that isn't it. And of course some say plugs and wires but I figured it would break up all the time if those two were the case. I'm in the same boat.
Staging Lane
Joined: Jul 2004
Posts: 52
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What did you guys gap the plugs to?
What fuel pumps are you using?
Are the fuel lines (feed and return) the same size in a V6 car as an LT1 car? If not you might be having flow problems.
Have you replaced, cleaned or rebuilt all the injectors? What about the fuel rail?
How are the O2 sensors?
Have you modifed the MAF? De-Screened or ported?
Could it be valve float? Just throwing out questions.
I wouldn't say that free-revving indicates there are no problems with the ignition as a weak spark may not show up until a load is put on the engine.
ZcarGuy
What fuel pumps are you using?
Are the fuel lines (feed and return) the same size in a V6 car as an LT1 car? If not you might be having flow problems.
Have you replaced, cleaned or rebuilt all the injectors? What about the fuel rail?
How are the O2 sensors?
Have you modifed the MAF? De-Screened or ported?
Could it be valve float? Just throwing out questions.
I wouldn't say that free-revving indicates there are no problems with the ignition as a weak spark may not show up until a load is put on the engine.
ZcarGuy
Perhaps by answering these questions, Not a 350 can potentially diagnose his problem. My plugs are gapped at .035" so I shouldn't be blowing the spark out. Fuel pump is a 255 lph so no problem there. My fuel lines are stock LT1 but flow plenty. Not sure on the V6 cars line size? Injector pulsewidths are not too high at all indicating they have plenty of duty cycle left. I don't have a fuel problem. My O2's are reading mid 800's to low 900 mVs but I'm in open loop anyway. MAF is stock for a reason. Valve float: no. Crane dual springs good for .700" lift. One thing I was talking with my dad about was my shift light. I have it wired up into the new Delteq. Under load, the shift light won't
illuminate at the correct RPM. It does come on immediately after the RPM it seems and then blinks intermittently for a couple hundred RPM. That means there's an erratic ignition signal. If my ignition was good, then I would have a true signal. If plugs and wires were bad or timing was too fast, I believe that I should still get a true signal to the shift light.
illuminate at the correct RPM. It does come on immediately after the RPM it seems and then blinks intermittently for a couple hundred RPM. That means there's an erratic ignition signal. If my ignition was good, then I would have a true signal. If plugs and wires were bad or timing was too fast, I believe that I should still get a true signal to the shift light.
Originally Posted by zcarguy
What did you guys gap the plugs to?
What fuel pumps are you using?
Are the fuel lines (feed and return) the same size in a V6 car as an LT1 car? If not you might be having flow problems.
Have you replaced, cleaned or rebuilt all the injectors? What about the fuel rail?
How are the O2 sensors?
Have you modifed the MAF? De-Screened or ported?
Could it be valve float? Just throwing out questions.
I wouldn't say that free-revving indicates there are no problems with the ignition as a weak spark may not show up until a load is put on the engine.
ZcarGuy
What fuel pumps are you using?
Are the fuel lines (feed and return) the same size in a V6 car as an LT1 car? If not you might be having flow problems.
Have you replaced, cleaned or rebuilt all the injectors? What about the fuel rail?
How are the O2 sensors?
Have you modifed the MAF? De-Screened or ported?
Could it be valve float? Just throwing out questions.
I wouldn't say that free-revving indicates there are no problems with the ignition as a weak spark may not show up until a load is put on the engine.
ZcarGuy
Staging Lane
Joined: Jul 2004
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Originally Posted by dhdenney
Perhaps by answering these questions, Not a 350 can potentially diagnose his problem. My plugs are gapped at .035" so I shouldn't be blowing the spark out. Fuel pump is a 255 lph so no problem there. My fuel lines are stock LT1 but flow plenty. Not sure on the V6 cars line size? Injector pulsewidths are not too high at all indicating they have plenty of duty cycle left. I don't have a fuel problem. My O2's are reading mid 800's to low 900 mVs but I'm in open loop anyway. MAF is stock for a reason. Valve float: no. Crane dual springs good for .700" lift. One thing I was talking with my dad about was my shift light. I have it wired up into the new Delteq. Under load, the shift light won't
illuminate at the correct RPM. It does come on immediately after the RPM it seems and then blinks intermittently for a couple hundred RPM. That means there's an erratic ignition signal. If my ignition was good, then I would have a true signal. If plugs and wires were bad or timing was too fast, I believe that I should still get a true signal to the shift light.
illuminate at the correct RPM. It does come on immediately after the RPM it seems and then blinks intermittently for a couple hundred RPM. That means there's an erratic ignition signal. If my ignition was good, then I would have a true signal. If plugs and wires were bad or timing was too fast, I believe that I should still get a true signal to the shift light.
If it uses the tach signal from the PCM and it's acting that way I'd say the Delteq is screwing something up or the PCM ignition routines have a problem. My guess is it'll trace back to either the optical section or the Delteq controller. Do you have an oscilliscope you can use to watch the wave form coming from the optical section? This would at least allow you to eliminate that if it's not the problem.
ZcarGuy
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Thread Starter
Teching In
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Thanks guys,
Here are the answers to your questions:
-Fuel pump is a 255 lph
-Injectors are used 30#, not cleaned, but the problem existed with the original 24# injectors
-I am using the springs from the LT4 hotcam kit though Dal and it didn't look like valve float on the dyno. We also went through the valves to make sure they were adjusted correctly.
-Optispark is reman from Dal
-Fuel Rail is stock
-MAF is stock
-Lines are from the V6, but I believe they are the same size as the V8 lines.
-Plugs are gapped at .035
-O2's are new but I don't have any scantool readings off them. The O2 readings from the dyno runs are in the 13.5 range at high rpm. A bit lean, but not enough to cause the miss feel.
-Aaron
Here are the answers to your questions:
-Fuel pump is a 255 lph
-Injectors are used 30#, not cleaned, but the problem existed with the original 24# injectors
-I am using the springs from the LT4 hotcam kit though Dal and it didn't look like valve float on the dyno. We also went through the valves to make sure they were adjusted correctly.
-Optispark is reman from Dal
-Fuel Rail is stock
-MAF is stock
-Lines are from the V6, but I believe they are the same size as the V8 lines.
-Plugs are gapped at .035
-O2's are new but I don't have any scantool readings off them. The O2 readings from the dyno runs are in the 13.5 range at high rpm. A bit lean, but not enough to cause the miss feel.
-Aaron
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Verdad Gallardo The light is wired into the Delteq. I talked to Pete at Delteq on the phone today. He said it sounds like it's receiving a poor low voltage signal which is exactly what I thought. So I need a new GM opti. Not a 350: we have almost identical setups as far as fuel and ignition goes. Pete seems to think that my optical is bad mainly because it's a reman. He said the remans just don't generate a true signal sometimes. Shane at Thunder Racing said the same thing so I'm banking on this being the problem. Costly yes, but I'm more worried about the labor 
TECH Enthusiast
Joined: May 2004
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From: St. Peters, MO
Eh, opti is not too bad. I got mine from Jason Cromer for like 235 shipped or something like that, and I performed the swap in like 4 hrs total in my garage. 4hrs wasn't too terrible I didn't think. Hopefully that is it though!
Thread Starter
Teching In
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Originally Posted by dhdenney
The light is wired into the Delteq. I talked to Pete at Delteq on the phone today. He said it sounds like it's receiving a poor low voltage signal which is exactly what I thought. So I need a new GM opti. Not a 350: we have almost identical setups as far as fuel and ignition goes. Pete seems to think that my optical is bad mainly because it's a reman. He said the remans just don't generate a true signal sometimes. Shane at Thunder Racing said the same thing so I'm banking on this being the problem. Costly yes, but I'm more worried about the labor
-Aaron
Staging Lane
Joined: Jul 2004
Posts: 52
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Originally Posted by Not a 350
Thanks dhdenney. Do you think the MSD cap and rotor will fix it, or should I get an entirely new opti?
-Aaron
-Aaron
http://www.dynotech-eng.com/dynaspark.htm
I don't have one of these or a delteq setup but I've heard good things about them, I've also heard good things about delteq as well, depends on who you talk to.
ZcarGuy
Yeah the cap and rotor is the high voltage side and the optical is the low voltage side so you wouldn't gain anything. Besides, I don't even think the MSD cap and rotor has hit the market yet. So I'm gonna get a new opti from GM and perhaps that will fix the problem. The Delteq will be a bad **** once I get a good signal from the optical.
Jordan57: I have the GenI so it's gonna cost me $340! The swap isn't bad no, but I've had that water pump off about 3 times in the last year and it's pissing me off!
Jordan57: I have the GenI so it's gonna cost me $340! The swap isn't bad no, but I've had that water pump off about 3 times in the last year and it's pissing me off!
TECH Enthusiast
Joined: May 2004
Posts: 549
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From: St. Peters, MO
Is there any way to swap to a vented? Whats involved with that? A dowel pin, timing chain cover clearancing? It almost seems worth it for that 100 or so bucks...idk though. Yeah if I had my waterpump off 3 times that would **** me the hell off...oh yeah I have and it does, but I kinda get excited to tear it down each time...its fun for me :-).
Originally Posted by Not a 350
I posted this as a reply to another thread, so my apologies for the double post:
My buddy has Firebird former V6 car that we put a '97 LT1 into. The motor starts breaking up at around 5500 rpm... kinda like it has hit a rev limiter. Sometimes it will power through, sometimes it won't. The revs drop so I don't think it is the trans slipping.
The motor has 34K on it, and we put a new optispark and MSD wires on it when we put it in. The heads were never off, but everything else was apart and it looked good. It has broke up at high RPMs since day one. Here are the new parts since:
Plugs
Coil
Wiring Harness
MAF
Injectors
Fuel Pump
Valve lash adjustment
Still does it. Could it be a bad Opti from GM? Would the MSD cap and rotor help? We are lost and my buddy is getting sick of throwing money at the car.
Mods are:
LT Headers
LT4 Hot cam
1.6 RRs
exhaust
cold air intake
Ed Wright tune
We have since taken it to Speed Inc for some dyno time and a better tune but it was breaking up so bad Jim couldn't get a good baseline pass.
Please help, we are at wit's end.
-Aaron
My buddy has Firebird former V6 car that we put a '97 LT1 into. The motor starts breaking up at around 5500 rpm... kinda like it has hit a rev limiter. Sometimes it will power through, sometimes it won't. The revs drop so I don't think it is the trans slipping.
The motor has 34K on it, and we put a new optispark and MSD wires on it when we put it in. The heads were never off, but everything else was apart and it looked good. It has broke up at high RPMs since day one. Here are the new parts since:
Plugs
Coil
Wiring Harness
MAF
Injectors
Fuel Pump
Valve lash adjustment
Still does it. Could it be a bad Opti from GM? Would the MSD cap and rotor help? We are lost and my buddy is getting sick of throwing money at the car.
Mods are:
LT Headers
LT4 Hot cam
1.6 RRs
exhaust
cold air intake
Ed Wright tune
We have since taken it to Speed Inc for some dyno time and a better tune but it was breaking up so bad Jim couldn't get a good baseline pass.
Please help, we are at wit's end.
-Aaron
Good luck, Ed
Originally Posted by dhdenney
Same problem here except I have a Delteq distributorless ignition. I thought it was supposed to eliminate the opti problems! I have three theories so far. My advance above 5000 is too high. I have a friend who is a gearhead from way back. He said I should be seeing about 38 advance that high up, not 44 or so like I have. I need to test that. My optical is bad. However, I have conflicting advice. Some say if it free revs past 5000 the optical is fine and is not load dependent. Some say it can cause a bad signal if it isn't perfect. It's the Delteq coils. Perhaps they're bad but I'm inclined to think that isn't it. And of course some say plugs and wires but I figured it would break up all the time if those two were the case. I'm in the same boat.
Good luck, Ed
Originally Posted by Ed Wright
If you are sitting still & reving it to 2800 or so, you will probably see 44 degrees. Also cruising down the street, light load. Not the same part of the spark map it uses for WOT. Sounds like your gearhead buddy doesn't understand how the PCM works. Ask him what kind of timing you would see on an older car under light loads with a vacuum advance connected. Same deal. That'll probably turn a light on for him.
Good luck, Ed
Good luck, Ed
Originally Posted by dhdenney
Yeah, he'll admit he doesn't understand fuel injection computers. I'll admit I don't understand them either, haha. I've just started to learn all this stuff and I logged some more data. My spark seems to be just fine. WOT sees only about 36-38 degrees. Can you buy the short harness from a dealer? How long are the wires? I might try that too. Just loathe splicing it.
Ed
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Teching In
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Ed,
I totally forgot to list that. Speed Inc suggested the short wire and let me borrow their spare. I am assuming theirs was a good one, but the car also broke up when we took it for a spin. I think they said it is about $75 from the dealer.
If I posted Dyno graphs, would it give you a better look?
Thank you,
-Aaron
I totally forgot to list that. Speed Inc suggested the short wire and let me borrow their spare. I am assuming theirs was a good one, but the car also broke up when we took it for a spin. I think they said it is about $75 from the dealer.
If I posted Dyno graphs, would it give you a better look?
Thank you,
-Aaron
Thread Starter
Teching In
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Also,
After looking at the dyno graphs, the problem is not fuel related. There were no lean spikes and A/F was steady at 13.0 at high RPM.
So that rules out injectors, fuel lines, pump, etc. It HAS to be spark.
when I pull the optispark I will take it apart and check the internals for loose parts, but I won't have the car a apsrt for a few weeks and am trying to look at it from all angles until then.
-Aaron
After looking at the dyno graphs, the problem is not fuel related. There were no lean spikes and A/F was steady at 13.0 at high RPM.
So that rules out injectors, fuel lines, pump, etc. It HAS to be spark.
when I pull the optispark I will take it apart and check the internals for loose parts, but I won't have the car a apsrt for a few weeks and am trying to look at it from all angles until then.
-Aaron