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Ls1 Backfire & Limp Mode At Wot Above 5k Rpm

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Tuned for 100 octane and your running 91 or 92? Do you know compression ratio?

You could be getting detonation and the knock sensors or pulling out timing. I assume the knock sensors are connected. High RPM and low cly air mass will most likely have the most timing advance.

No sure on MEFI, but on the factory computer you can set sensors to not report errors.

Can you talk to the previous owner or turnkey?

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Tuned for 100 octane and your running 91 or 92? Do you know compression ratio?

You could be getting detonation and the knock sensors or pulling out timing. I assume the knock sensors are connected. High RPM and low cly air mass will most likely have the most timing advance.

No sure on MEFI, but on the factory computer you can set sensors to not report errors.

Can you talk to the previous owner or turnkey?

Yes it is MEFI, I dont know who the previous owner was. the guys bought it from took it in on trade and really didnt know what they had.

when I clicked on octane on my scanpro program is said 99.6 so Im almost positive it must be tuned for 100 octane which i just found out last night.

and yes i think it is 91 i am running. (premium from the gas station) the car was an 06 or 07 and i have not talked to turn key just because it was so old and the people with similar issues were told it was a voltage drop. I made that change and nothing helped.

Im really hoping the octane is the problem and I didnt cause any damage to the engine. the compression on the cylinders was between 160 psi and 180psi.

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I still think it has to do with voltage drop, check and clean the grounds on the wire harness to the block, also check the condition of the wire from the alternator to the starter. I have also heard of alternators doing this under load at high speed. On the fuel filter make sure its not a paper filter in front of the fuel pump starving it for fuel. I'm not a tuner but when mine was tuned they have timing values set, I don't think it has any thing to do with octane other then what the tuner sets for timing. If it does have a knock sensor its pulling timing if it needs but I cant see it going into limp mode for that.

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First off...I'd give CBM a call direct. IF they can't help you, no one can.

For your crank sensor, I think you got either a bad one, or one for the different size reluctor.

Have you checked the connections for all of your sensors, to make sure they are tight and no corrosion? Since it runs until you stab the throttle, it seems that most everything is good.

Like almost everyone has said, you HAVE TO KEEP THE CORRECT VOLTAGE TO COMPUTER or your woes begin to start, in fact there is a thread here (and CBM talked about this) where if the voltage is too low, bad things happen to mechanical parts)

I'd say your timing is off, either because it's off, or it is sensitive to the fuel.

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I agree about calling CBM on this one. They know MEFI. I don't think it could be pulling out enough timing, but if the knock sensors go off that much, it may go into limp.

I agree on checking ground though. Seen ground/voltage do crazy things. Keep them clean. I run multiple grounds including a large ground strap to the motor.

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Tuned for 100 octane and your running 91 or 92? Do you know compression ratio?

You could be getting detonation and the knock sensors or pulling out timing. I assume the knock sensors are connected. High RPM and low cly air mass will most likely have the most timing advance.

No sure on MEFI, but on the factory computer you can set sensors to not report errors.

Can you talk to the previous owner or turnkey?

Yes it is MEFI, I dont know who the previous owner was. the guys bought it from took it in on trade and really didnt know what they had.

when I clicked on octane on my scanpro program is said 99.6 so Im almost positive it must be tuned for 100 octane which i just found out last night.

and yes i think it is 91 i am running. (premium from the gas station) the car was an 06 or 07 and i have not talked to turn key just because it was so old and the people with similar issues were told it was a voltage drop. I made that change and nothing helped.

So you put a relay in and confirmed voltage?

Im really hoping the octane is the problem and I didnt cause any damage to the engine. the compression on the cylinders was between 160 psi and 180psi.

highly doubtful its the octane of fuel that your running, unless you bought some shitty no name station, then its probably 87 octane

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You guys on this site are awesome and I cannot tell you how much I appreciate the help.

Fuel pressure - seems good - runs at 58PSI even under a load.

alternator - with all lights and fans on is putting out 14.16 volts at the battery

TPS - .75 volts at closed throttle 4.75 volts at 96% open throttle

fuel - now has 100 octane - still having issue

coolant sensor voltage is 2.49 volts

MAP sensor voltage 4.49

found a loose ground last night and tightened it (back of the head). I don't know how the hell it came loose, and I don't think it was loose before I pulled the motor and did the clutch, and the car had the same problem before that. regardless I will test to see if that ground was the issue tonight. if its not I will chase all of the wires to make sure they all are not damaged and properly connected

I still need to do a couple of other things you have all recommended. I need to pull crank sensor and check the reluctor wheel.

Calling CBM direct is a great option that I did not know I had before this thread. Its amazing that the company will walk you through helping with diagnosis when it is not their motor and you are not a previous customer. Most companies tell you to bring the car in to look at it and what to start the billing process.

This has become a challenge for me at this point and once my mind is stuck on something it drives me nuts until it's resolved. I drove the heck out of the car all season and I just shifted early not utilizing all of the power and it never bothered me too much. Now that I am focused on fixing it the damn thing is driving me bat sh** crazy.

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Tuned for 100 octane and your running 91 or 92? Do you know compression ratio?

You could be getting detonation and the knock sensors or pulling out timing. I assume the knock sensors are connected. High RPM and low cly air mass will most likely have the most timing advance.

No sure on MEFI, but on the factory computer you can set sensors to not report errors.

Can you talk to the previous owner or turnkey?

Yes it is MEFI, I dont know who the previous owner was. the guys bought it from took it in on trade and really didnt know what they had.

when I clicked on octane on my scanpro program is said 99.6 so Im almost positive it must be tuned for 100 octane which i just found out last night.

and yes i think it is 91 i am running. (premium from the gas station) the car was an 06 or 07 and i have not talked to turn key just because it was so old and the people with similar issues were told it was a voltage drop. I made that change and nothing helped.

So you put a relay in and confirmed voltage?

Im really hoping the octane is the problem and I didnt cause any damage to the engine. the compression on the cylinders was between 160 psi and 180psi.

highly doubtful its the octane of fuel that your running, unless you bought some shitty no name station, then its probably 87 octane

How do I check the voltage out of the wire at WOT? I checked it when the car is running and sitting their. also the laptop is saying that the ecu is never going under 11.5 volts when driving it. Once the issue happens (backfire, flame out of exhaust and limp mode) the computer just goes crazy like all of the sensors shut off as if the ecu doesn't know what to do for a second.

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I still think it has to do with voltage drop, check and clean the grounds on the wire harness to the block, also check the condition of the wire from the alternator to the starter. I have also heard of alternators doing this under load at high speed. On the fuel filter make sure its not a paper filter in front of the fuel pump starving it for fuel. I'm not a tuner but when mine was tuned they have timing values set, I don't think it has any thing to do with octane other then what the tuner sets for timing. If it does have a knock sensor its pulling timing if it needs but I cant see it going into limp mode for that.

x2 ^^^^^^^^^^^^^^

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One other thing you can test is to see if you have the same voltage with everything turned on, all lights, radio(s). If it drops it is more than likely dropping at WOT. Look at wiring, ground connections, connectors for corrosion.

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:ty::sdance::thanks::dancer::rock:

OK I know this might be a little overboard with the emojis, (had to delete a bunch to get message to come across) but I'm almost 100% positive that the problem is resolved. I took the car out last night after tightening the ground on the back of the head and I ran the sh** out of if and tried to make the problem occur. Wouldn't happen!

My theory...... You guys know your business. I guarantee it was a voltage drop that was originally causing the problem. Running a direct wire with a relay solved problem one.

Then My stupid A$$ put a new clutch in in mid season. Somehow I forgot to tighten the ground and just my luck this would cause the EXACT same problem leaving me to think that putting the relay in didn't solve the problem. whats the chances of that happening?

I hate to be too confident and jinx myself before I take it out for a solid weekend, but from past experience everything I did to it last night would have made the problem happen and it didn't. You all on here are some great people and I cannot thank you enough for the help.

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Congrats! It always feels good to get the problem solved.

Thanks for letting us know the end result.

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Nice work John, can wait to go break some chit tomorrow see you in the AM, you where fast with it running funky so it will be interesting tomorrow,

Markha we will send you pics due to you not coming out with us LOL

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I'm not sure if you figured out the gas thing but "tuned" at 99.6 octane could very well be E85 and that's a lot different than 100 octane race. You can probably tell if it is by the injector duty cycle and fuel trim chart if it's e85 or not. (Just a guess on my part)

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This is a good start for a weekend. Keep the revs up.

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Congrats on fixing the problem.

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Well,

Saturday we did an early morning run to Dumont. There were some sick cars that met us out there. My car ran on point the whole first run... At the end of the second run it started acting up again. I went from an extreme high thinking my problem was behind me to a pretty bad let down. Every time I got up high in the RPM again it would cut out. I brought it home and started cleaning and chasing grounds. I re-grounded damn near everything, and the grounds didn't change a thing. I replaced the relay just because I had an extra, AND I ran another dedicated line from the battery to the main constant hot wire on the ecu(the orange wire in spot 1). I took the car back out and BAM. running perfect again. Even if the problem happens again I am pretty confident I can figure it out. It is just like all of you guys have been saying. It has to be a voltage drop. I am pretty confident the problem is fixed but I'm not counting any farm animals yet. here are a few pics of the cars sitting in camp!

post-94813-1461292881_thumb.jpg

post-94813-1461292891_thumb.jpg

post-94813-1461292904_thumb.jpg

post-94813-1461292915_thumb.jpg

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Big J, you have to post of the ground you sent me in the text, I think it will help out for the future,

Had a great time, one of the best day trips I have had

Rick10

Jetjock

Sandroosten

J Alper

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I had a problem recently with my fuse holder causing the car to cut out under load. Check to make sure the fuses are all in there tight and there isn't any corrosion.

It was the ign fuse in the mefi harness.

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I had a problem recently with my fuse holder causing the car to cut out under load. Check to make sure the fuses are all in there tight and there isn't any corrosion.

It was the ign fuse in the mefi harness.

I think John has it figured out now, dedicated power to the relay, sand down the paint on the ground wire and a new non china relay,

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