Can a 40-100 O2 reading cause an 80 hp loss?
10-04-2011, 02:41 PM
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Can a 40-100 O2 reading cause an 80 hp loss? In short, I shipped my car to a sponsor. The car made 427/415. with a 223/230 cam and 243's and LT's at 26*. When i got the car back though it only makes 350 rwhp. the air/fuel goes up to 15:1 The tuner says that he sees that there is a problem in bank one. usually it's a 40 mv difference. I have changed spark plugs, coils, wires and o2 sensors on that side and the problem remains. I checked the grounds too.He says that's why the car is lean and loosing 80 hp. My old cam had two really bad spots and the lifters weren't changed because the shop said they used a boroscope. I was thinking the old lifters have now ground into the cam. The problem is, I don't hear anything bad even with valve covers off. The car has no codes. The timing is set to 21 now but the tuner said it didn't make a difference. I don't want to pull a good motor with no smoke or problems if I don't have to. Just wondering what your thoughts are.
Could it be the cam?
the 26 to 21*?
What gives?
Lastly I can literally feel the car in third when it looses power as if I hit a limiter around 5000 rpm. but limiter is 6800.
Could it be the cam?
the 26 to 21*?
What gives?
Lastly I can literally feel the car in third when it looses power as if I hit a limiter around 5000 rpm. but limiter is 6800.
10-04-2011, 03:35 PM
#2
Wow. A sponsor here handed you back a car in that shape? Lifters should have been replaced.
When you say it feels like it hits a rev limiter at 5 grand, does it break up? Or does it just nose over and loose power?
I would start by checking your fuel pressure, then check to make sure you're running on all 8 cylinders. There's several ways to do this. Best way is with a temp gun, check the header temps.
What diagnostic tools and equipment do you have to work with?
When you say it feels like it hits a rev limiter at 5 grand, does it break up? Or does it just nose over and loose power?
I would start by checking your fuel pressure, then check to make sure you're running on all 8 cylinders. There's several ways to do this. Best way is with a temp gun, check the header temps.
What diagnostic tools and equipment do you have to work with?
10-04-2011, 04:52 PM
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Wow. A sponsor here handed you back a car in that shape? Lifters should have been replaced.
When you say it feels like it hits a rev limiter at 5 grand, does it break up? Or does it just nose over and loose power?
I would start by checking your fuel pressure, then check to make sure you're running on all 8 cylinders. There's several ways to do this. Best way is with a temp gun, check the header temps.
What diagnostic tools and equipment do you have to work with?
When you say it feels like it hits a rev limiter at 5 grand, does it break up? Or does it just nose over and loose power?
I would start by checking your fuel pressure, then check to make sure you're running on all 8 cylinders. There's several ways to do this. Best way is with a temp gun, check the header temps.
What diagnostic tools and equipment do you have to work with?
10-06-2011, 09:14 AM
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If you are running 15 to 1 a/f ratio that is way lean. Lean is hot and very bad. You should be running in the 13 to 1. LS engine make best power at 28 deg timing. If you fix the timing and air/fuel you will make alot more power.
10-06-2011, 01:33 PM
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As a sanity-check-rule-of-thumb-only, at WOT your front NBO2 sensors should be reading close to or above 900mV...
if they read less, then something is wrong, either:
- the NBO2 sensors are bad (which has no relevance to the topic),
- the AFR is way too lean;
[ of course, always check the AFR with a wideband ]
The AFR being lean and the spark timing being too low may possibly account for losing 80 HP...
question: was spark timing set low because engine was knocking (probably due to lean AFR)...?
if they read less, then something is wrong, either:
- the NBO2 sensors are bad (which has no relevance to the topic),
- the AFR is way too lean;
[ of course, always check the AFR with a wideband ]
The AFR being lean and the spark timing being too low may possibly account for losing 80 HP...
question: was spark timing set low because engine was knocking (probably due to lean AFR)...?
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10-06-2011, 08:32 PM
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Results driver side front to back:
250/247/268/220
Passenger side front to back:
200/248/277/253
Now I'm really confused, I just assumed that the old bad lifters had eaten into the new cam and caused a change in the profile. Even with a stethescope, I cant hear bad lifters though. Also my tuner said the problem is with bank one so I've changed, plugs, wires and coil packs all on bank one(driver side, I assume).
However, the coldest cylinder is on the passenger side.
At WOT, my reading are bank one 924, bank 2 959 on street 985, 1016 on a dyno pull. I think a spark plug wire may have been unplugged on that run though. I'm not sure. Car made 350 and went way lean on a dynojet. However the dyno sheet that the sponsor gave me had it making 424/414 on a mustang dyno.
As for timing, the cam is a 223/230. They said it made 427/404 at 26* but when I asked to pull timing for nitrous, It made 424/415 so that's where they left it and shipped the car back.
250/247/268/220
Passenger side front to back:
200/248/277/253
Now I'm really confused, I just assumed that the old bad lifters had eaten into the new cam and caused a change in the profile. Even with a stethescope, I cant hear bad lifters though. Also my tuner said the problem is with bank one so I've changed, plugs, wires and coil packs all on bank one(driver side, I assume).
However, the coldest cylinder is on the passenger side.
At WOT, my reading are bank one 924, bank 2 959 on street 985, 1016 on a dyno pull. I think a spark plug wire may have been unplugged on that run though. I'm not sure. Car made 350 and went way lean on a dynojet. However the dyno sheet that the sponsor gave me had it making 424/414 on a mustang dyno.
As for timing, the cam is a 223/230. They said it made 427/404 at 26* but when I asked to pull timing for nitrous, It made 424/415 so that's where they left it and shipped the car back.
10-06-2011, 08:40 PM
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[QUOTE=edcmat-l1;15468266]Wow. A sponsor here handed you back a car in that shape? Lifters should have been replaced.
When you say it feels like it hits a rev limiter at 5 grand, does it break up? Or does it just nose over and loose power?
I would start by checking your fuel pressure, then check to make sure you're running on all 8 cylinders. There's several ways to do this. Best way is with a temp gun, check the header temps.
What diagnostic tools and equipment do you have to work with?[/QUOTE/]
Also, it seems as if the car hits a plateau, and stops pulling early somtimes.then sometimes it pauses and picks up.
When you say it feels like it hits a rev limiter at 5 grand, does it break up? Or does it just nose over and loose power?
I would start by checking your fuel pressure, then check to make sure you're running on all 8 cylinders. There's several ways to do this. Best way is with a temp gun, check the header temps.
What diagnostic tools and equipment do you have to work with?[/QUOTE/]
Also, it seems as if the car hits a plateau, and stops pulling early somtimes.then sometimes it pauses and picks up.
10-07-2011, 01:58 PM
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10-09-2011, 08:46 AM
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check out this file. At 5900 in 3rd gear, there is actually a 300mV difference. This is the power loss I feel when driving, then the car starts to pick back up. It seems as if the lobes of the cams were eaten then the loss would be there all the time. Please guys if there is anything that comes to mind let me know. The coldest cylinder is actually on Bank 2 which accourding to the o2 readings is the good side of the motor.
Could a ground affect one side of the motor?
Does it appear to be a tuning problem?
I don't know the next steps to take.
Could a ground affect one side of the motor?
Does it appear to be a tuning problem?
I don't know the next steps to take.
10-09-2011, 10:56 AM
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I think it's a mechanical problem. If the original cam had flat spots (intake or exhaust lobe?) the lifters should have been changed as well or at the very least pulled and inspected before the new cam was installed. Based on the temp gun readings, I would pull the cam and lifters for inspection or further inspect the valve train for those two cylinders. Do you have pics of the old cam?
10-09-2011, 10:31 PM
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Pics of the cam enclosed. Blue marks show the two beat up lobes. Just not sure which cylinder they coincide with.
