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Discussion Starter #1
Hi guys,

I have a noticeable power loss on my V8 that I can not only feel in the seat of my pants, but the track-day telemetry clearly shows the reduction in acceleration.

My boost looks great and intake temperatures look perfect, and I have no codes or CEL. The performance drop feels like a lack of ignition advance and as the RPMs increase the power peeters out (just like you'd get with lack of ignition advance).

In addition, the telemetry I collect from the OBD-II port looks really strange and I have never seen this before. During high-demand periods, the ECU is no longer providing query data and there will be a stretch of 10 seconds at a time (on the front and back straightaway) where the ECU isn't providing any data samples at all. It's as if the ECU is too busy with something to respond to polling requests.

So, is this symptomatic of something the group is familiar with? Do I have a cam sensor flaking out resulting in the ECU doing double-time trying to maintain timing with skipped pulses or whatever and since its flaking out I'm getting crappy ignition timing and lack of advance? Any other ideas?

Knut
 

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Just a wild a-- guess. Bad fuel injectors won't throw a code but can have unpredictible symptoms. The OEM injectors have a definite life, maybe they are bad. Another possibility is a restricted exhaust. That can cause a drop off in power. A plugged cat can do that.
David Teitelbaum
 

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Discussion Starter #3
Thought I'd share and reiterate a couple additional details around my reduced power. The power reduction is noticeable but not a limping around power loss. The car runs beautifully.

There is no CEL and no codes. The onset was sudden and not progressive (one lap was a great lap and the next lap it was sluggish). I have sports cats on the car. All my previous telemetry collection never had any missing OBD-II query samples, but the car now predictably stops responding to OBD-II queries during high-load conditions.

What sensor does the computer in the V8 use to control ignition timing (there must be a crank or cam sensor) and is that sensor at all prone to failure?

Knut
 

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Wingless Wonder
1988 Esprit Turbo
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I know, I know, no CEL...

But it almost sounds as if the ECM has put the car into some type of limp mode.



Have you tried resetting the ECU or disconnecting the battery for 30 minutes?
 

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More then likely the bracket on the throttle pedal that the cable attaches to is bent and you are not getting true full throttle when you put the pedal down to the mat.
Common issue on the V8, the convoluted (in my opinion anyway) throttle linkage puts considerable strain on the connection point @ the pedal bending it over time.
Check this before getting crazy chasing ecu gremlins...
 

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More then likely the bracket on the throttle pedal that the cable attaches to is bent and you are not getting true full throttle when you put the pedal down to the mat.
Common issue on the V8, the convoluted (in my opinion anyway) throttle linkage puts considerable strain on the connection point @ the pedal bending it over time.
Check this before getting crazy chasing ecu gremlins...
Real easy to check the throttle position sensor and see if you can get 100%. Without a code you have to go hunting and you will not always guess correctly. I say start with the simple stuff and then work your way up to the more complicated (expensive) possibilities. I would start with fuel. Check the fuel pressure. A low fuel pressure does not throw a code. Maybe a stuck pressure regulator? Then maybe a bad injector. Maybe a dirty fuel filter.
David Teitelbaum
 

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Discussion Starter #8
Real easy to check the throttle position sensor and see if you can get 100%. Without a code you have to go hunting and you will not always guess correctly. I say start with the simple stuff and then work your way up to the more complicated (expensive) possibilities. I would start with fuel. Check the fuel pressure. A low fuel pressure does not throw a code. Maybe a stuck pressure regulator? Then maybe a bad injector. Maybe a dirty fuel filter.
David Teitelbaum

The throttle position reads 100% and it's not a bracket issue.

Does the knock sensor often fail and if so does it ever fail by becoming too sensitive resulting in the ECU getting a lot of knock signals and having it retard timing? I guess I could simply make a test run with my laptop connected and check the knock counts.
 

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The throttle position reads 100% and it's not a bracket issue.

Does the knock sensor often fail and if so does it ever fail by becoming too sensitive resulting in the ECU getting a lot of knock signals and having it retard timing? I guess I could simply make a test run with my laptop connected and check the knock counts.
There is also a rough road sensor that is supposed to cancel knocks caused by rough roads. But if either one was going off you would see stored codes, if not a lite MIL. Bad fuel could cause the knock sensor to operate but again, you would see codes.
David Teitelbaum
 

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There is a "rough road sensor" that is located at the left rear of the engine compartment bolted to the frame that records vertical movement and will make the ecu disregard knock counts that coincide with these vibrations. It is possible that this has failed.
Would be a good idea to check your fuel pressure @ idle and under load. It is common for the hose line connection in the tank from the main pump to rupture and limit your fuel pressure. This would cause a slight lean condition first which would cause knock/ping and a subsequent pull back on the timing/power loss. There may be no codes generated right away as it takes time for the long term fuel trims to go far enough out.
 

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Discussion Starter #11
Timing advance data from a test run

Hi guys,

I did a little data logging during a couple test pulls and wanted to get some insight from the team. I'll post a graph with some data after I re-take it with fewer channels captured to improve the sampling rate.

All the mundane stuff is fine (throttle position sensor reads 100%, temperatures are good, etc). Also, the mixture is fine and the O2 sensor readings indicate no hint of fuel starvation and at wide open throttle and full boost the O2 sensor is reading a little rich which I'm sure is intentional to protect the engine. The recorded boost is exactly where it should be.

However, the timing advance does indeed look pretty strange. At low load and partial throttle leading up to the pull I have about 28 degrees. When I put the hammer down the advance is retarded and drops back to 16 degrees by the time the RPM's are at 3000 and boost is building. When at 5000 RPM and full boost the timing advance is down to only 9 degrees. After a gear change and hammer down again the advance comes down to 7.5 degrees at 5500 RPM and full boost.

With such retarded timing at high RPMs it's no wonder I have no acceleration at speed.

So now for a couple questions -- what kind of timing advance should I be expecting at reasonable engine RPM's? I'd expect far more than I'm seeing, but I'm not sure what is typical since I don't have a baseline that recorded this on my car.

What are likely culprits for my ECU retarding the timing so badly? The knock sensor seems like a primary input the ECU uses to retard timing, so is it susceptible to failing in a way that makes it falsely trigger?

Knut
 

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Hi guys,

I did a little data logging during a couple test pulls and wanted to get some insight from the team. I'll post a graph with some data after I re-take it with fewer channels captured to improve the sampling rate.

All the mundane stuff is fine (throttle position sensor reads 100%, temperatures are good, etc). Also, the mixture is fine and the O2 sensor readings indicate no hint of fuel starvation and at wide open throttle and full boost the O2 sensor is reading a little rich which I'm sure is intentional to protect the engine. The recorded boost is exactly where it should be.

However, the timing advance does indeed look pretty strange. At low load and partial throttle leading up to the pull I have about 28 degrees. When I put the hammer down the advance is retarded and drops back to 16 degrees by the time the RPM's are at 3000 and boost is building. When at 5000 RPM and full boost the timing advance is down to only 9 degrees. After a gear change and hammer down again the advance comes down to 7.5 degrees at 5500 RPM and full boost.

With such retarded timing at high RPMs it's no wonder I have no acceleration at speed.

So now for a couple questions -- what kind of timing advance should I be expecting at reasonable engine RPM's? I'd expect far more than I'm seeing, but I'm not sure what is typical since I don't have a baseline that recorded this on my car.

What are likely culprits for my ECU retarding the timing so badly? The knock sensor seems like a primary input the ECU uses to retard timing, so is it susceptible to failing in a way that makes it falsely trigger?

Knut
A N/A motor would be pulling 30+ degrees of timing at the higher end of the rpm range, boosted would usually drop one degree per pound of boost (just a rough number) so you should be in the mid twenties under load at those rpms.
Did you record any knock counts during your logging? The knock sensor can be a prime suspect to pulling ignition but intake air temps can be just as important. Do some more data logging focusing on the knock counts and IAT sensors in relation to rpm/boost/ign advance.
 

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Hi guys,

I did a little data logging during a couple test pulls and wanted to get some insight from the team. I'll post a graph with some data after I re-take it with fewer channels captured to improve the sampling rate.

All the mundane stuff is fine (throttle position sensor reads 100%, temperatures are good, etc). Also, the mixture is fine and the O2 sensor readings indicate no hint of fuel starvation and at wide open throttle and full boost the O2 sensor is reading a little rich which I'm sure is intentional to protect the engine. The recorded boost is exactly where it should be.

However, the timing advance does indeed look pretty strange. At low load and partial throttle leading up to the pull I have about 28 degrees. When I put the hammer down the advance is retarded and drops back to 16 degrees by the time the RPM's are at 3000 and boost is building. When at 5000 RPM and full boost the timing advance is down to only 9 degrees. After a gear change and hammer down again the advance comes down to 7.5 degrees at 5500 RPM and full boost.

With such retarded timing at high RPMs it's no wonder I have no acceleration at speed.

So now for a couple questions -- what kind of timing advance should I be expecting at reasonable engine RPM's? I'd expect far more than I'm seeing, but I'm not sure what is typical since I don't have a baseline that recorded this on my car.

What are likely culprits for my ECU retarding the timing so badly? The knock sensor seems like a primary input the ECU uses to retard timing, so is it susceptible to failing in a way that makes it falsely trigger?

Knut
One more note,
The fact that the lambda sensor read on the rich side doesn't really mean much as they are narrow band so rich is just south of stoich (14.7/1) so even know it is "rich" it may not be rich enough to avoid knock under the load/boost conditions.
 

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Hi guys,

I did a little data logging during a couple test pulls and wanted to get some insight from the team. I'll post a graph with some data after I re-take it with fewer channels captured to improve the sampling rate.

All the mundane stuff is fine (throttle position sensor reads 100%, temperatures are good, etc). Also, the mixture is fine and the O2 sensor readings indicate no hint of fuel starvation and at wide open throttle and full boost the O2 sensor is reading a little rich which I'm sure is intentional to protect the engine. The recorded boost is exactly where it should be.

However, the timing advance does indeed look pretty strange. At low load and partial throttle leading up to the pull I have about 28 degrees. When I put the hammer down the advance is retarded and drops back to 16 degrees by the time the RPM's are at 3000 and boost is building. When at 5000 RPM and full boost the timing advance is down to only 9 degrees. After a gear change and hammer down again the advance comes down to 7.5 degrees at 5500 RPM and full boost.

With such retarded timing at high RPMs it's no wonder I have no acceleration at speed.

So now for a couple questions -- what kind of timing advance should I be expecting at reasonable engine RPM's? I'd expect far more than I'm seeing, but I'm not sure what is typical since I don't have a baseline that recorded this on my car.

What are likely culprits for my ECU retarding the timing so badly? The knock sensor seems like a primary input the ECU uses to retard timing, so is it susceptible to failing in a way that makes it falsely trigger?

Knut
Things that affect spark control:
engine speed
engine position
MAP
BARO
throttle position
coolant temp
inlet air temp
knock sensor
wheel speed

It could be you did not have a problem often enough or serious enough yet to store a code and lite the MIL, it may take a few cycles. It could be an intermittent problem from one of the sensors and although they all look like they are working one of them drops out of range and the ECU defaults to a stored value. Another possibility is the ECU is is having internal problems and cannot output an error code for it. The knock sensor can be tested directly by knocking the motor with an bar and watching the output. Same thing with the R/R sensor. Might be time to substitute an known, good ECU. If you can, graph each sensor and look for spikes and drop-outs. If you don't see any it leads back to the ECU.
David Teitelbaum
 

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Discussion Starter #15
A N/A motor would be pulling 30+ degrees of timing at the higher end of the rpm range, boosted would usually drop one degree per pound of boost (just a rough number) so you should be in the mid twenties under load at those rpms.
Did you record any knock counts during your logging? The knock sensor can be a prime suspect to pulling ignition but intake air temps can be just as important. Do some more data logging focusing on the knock counts and IAT sensors in relation to rpm/boost/ign advance.
My intake air temps look great as I'm intercooled and for the test I hadn't sustained sufficient boost to heat things up. Inlet air temps were 40C at the end of the pulls (starting in mid 30's at the beginning).

My logger (Gendan) doesn't seem to support reading the knock counts. Which logger provides best support for the V8 that I might switch to? I suspect false knock triggers and looking at the knock counts would obviousy be a big help in getting a better handle on things.

Knut
 

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Wingless Wonder
1988 Esprit Turbo
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Another W.A.G. from a 4 cyl guy:


Modern computer-controlled engines can be sensitive to a "clean" ground. (In fact, some auxiliary "earthing kits" are sold as performance enhancers.)

Have you verified a low resistance back to battery negative? Did Lotus still use a solitary earth braid from the RH motor mount on the V8s?
 

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Another W.A.G. from a 4 cyl guy:


Modern computer-controlled engines can be sensitive to a "clean" ground. (In fact, some auxiliary "earthing kits" are sold as performance enhancers.)

Have you verified a low resistance back to battery negative? Did Lotus still use a solitary earth braid from the RH motor mount on the V8s?
That's a great thought Atwell; even if Knut's problem is different; low, or unstable power to the ECU certainly could manifest in odd ways. Wonder what the current draw is on the ECU and how is it grounded.
:clap:
 

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That's a great thought Atwell; even if Knut's problem is different; low, or unstable power to the ECU certainly could manifest in odd ways. Wonder what the current draw is on the ECU and how is it grounded.
:clap:
There is a main grounding point at one of the upper bolts on the bell housing for the engine wiring harness. Grounding isn't a big problem on the V-8's unless someone didn't put all of the wires back. The only good data logger I know of that can also do snapshots is a Tech 1. Bad power or grounds would manifest itself in other problems too and would not necessarily be so repeatable. One of the subtle clues here is that everything was running fine and all of a sudden this problem appeared and is very repeatable. Something changed and is of such nature that it can't or won't change back. At least you will know when you fixed it! When you have an intermittent you can't be sure for a while, always wondering if it will come back! Was any service work of any kind done just before the symptoms appeared?
David Teitelbaum
 

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That's a great thought Atwell; even if Knut's problem is different; low, or unstable power to the ECU certainly could manifest in odd ways. Wonder what the current draw is on the ECU and how is it grounded.
:clap:
Actually, the theory is that good, clean ground paths provides stable and accurate readings from the various sensors, to the ECU.

Otherwise, it's GIGO. (Garbage In, Garbage Out) :shrug:
 

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There is a main grounding point at one of the upper bolts on the bell housing for the engine wiring harness. Grounding isn't a big problem on the V-8's unless someone didn't put all of the wires back. The only good data logger I know of that can also do snapshots is a Tech 1. Bad power or grounds would manifest itself in other problems too and would not necessarily be so repeatable. One of the subtle clues here is that everything was running fine and all of a sudden this problem appeared and is very repeatable. Something changed and is of such nature that it can't or won't change back. At least you will know when you fixed it! When you have an intermittent you can't be sure for a while, always wondering if it will come back! Was any service work of any kind done just before the symptoms appeared?
David Teitelbaum
Building on what David just pointed out, this is a hard fail with repeatable results. I have to reiterate the importance of verifying your fuel pressure at idle and under load. Ruptured soft wall fuel line in tank is a very common problem with V8's of this vintage. As I stated before the fact that you see a rich condition on your narrow band lambda doesn't mean you have adequate fuel for the higher boost situation. You stated that your IAT's are good so the next best culprit for pulling timing in the fashion you are seeing is knock (which you can not log with your current scanner). I'd verify your fuel supply before going any further, slight fuel starvation seems to fit your symptoms.
 
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