[ksgrimsr]

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

 

[ksgrimsr]

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

 

[ksgrimsr]

Oh! does it boost over 5 psi?

I have full boost of around 0.75 bar

 

[ksgrimsr]

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.

 

[ksgrimsr]

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

 

[ksgrimsr]

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

 

[ksgrimsr]

A little snip it from the repair manual about the 918's knock sensor...

EMM.2 - T KNOCK SENSOR
The ignition timing required for optimum performance can lead, under certain operating conditions;’ to
detonation of the fuel mixture in the combustion chamber, causing excessive heat and pressures and a characteristic
‘knocking’ noise. ...

When the knock sensor detects the onset of detonation, the ECM first rapidly retards ignition timing to a
safe level..

Thanks for the helpful snippet. I'm familiar with this section of the manual and it's the primary reason I have been asking so many questions about the knock sensor and its failure modes (whether it fails in a way that makes it trigger all the time) and how to confirm it is indeed triggering by measuring it (my OBD-II reader doesn't cut it).

In the absence of a Tech-1 what are my options for measuring the knock sensor? I have already read the section of the manual mentioning the 2.5V bias and A/C voltage the sensor induces, etc., but it's a little vague about where I might be able to tap into the signal to make a measurement. Is there a convenient harness connector that is accessible that I can gain access to this signal conveniently?

The way I see it there are three options I need to narrow down with some diagnosis:
1) It is indeed knocking (and then I can chase down the reason for the knock of which a few possibilities have been suggested)
2) It is not knocking and the sensor has failed in a way that is resulting in it sending spurious knock signals to the computer (in which case I have a bad sensor to replace)
3) It is not knocking but I have something else rattling around in the engine such as a bad rod bearing that is causing a slap that is triggering the knock sensor (any mechanical ping will trigger the knock sensor and it doesn't have to be induced by detonation).

Before I attempt to fix something, I'm first striving to properly diagnose what is going on so I know what to fix and why. My first angle is to see if I can determine whether the knock sensor is indeed triggering and then proceed to determine why if that's indeed so. So in the absence of a Tech-1, does anyone have info on how I'd go about measuring the knock sensor signal?

Thanks all for your help!

Knut

 

[ksgrimsr]

Got my hands on a Tech-1 with the Lotus V8 module in it (thanks to Guy). I'll do a couple measurements this coming weekend and post what I find.

I have a new knock sensor on its way just in case it is the culprit. My fear is that there is something banging around that is triggering the knock sensor which is a little concerning since worst case it's a rod bearing slapping around. My heat shields are split and rattling but I don't think that has the kind of impact that would trigger the knock sensor.

Knut

 

[ksgrimsr]

Knock sensor access

In the handbook it mentions "... remove or partially remove the intake plenum to provide sufficient access to the sensor..."

So does this imply that sufficient access to the sensor can be achieved by not completely removing the plenum? Can it be released and simply lifted at the front to gain sufficient access?

 

[ksgrimsr]

Tech-1 readings from performance pulls

So I had a chance to plug in the Tech-1 I borrowed with the Esprit V8 module in it (thanks Guy) and take a couple measurements with it on my lap while doing some performance pulls.

Since it only displays 2 lines of live data at a time I first looked at the knock sensor voltage and the KNK IGN Retard value. The knock sensor voltage came up to about two tenths of a volt during the pulls and the KNK IGN Retard value came up to 0.75 degrees, which is nothing.

I next monitored IGN Advance and KNK IGN Retard values and indeed during the pulls the advance drops down (dropped to 7.5 degrees in my pulls which were a little less aggressive) while the knock retard rises to the modest 0.75 value.

I thought maybe the KNK IGN Retard value displayed might have the decimal point in the wrong place, but when I just rev the engine not under load I get 30 degrees of advance with the same 0.75 degree knock retard value so I don't think there is some snafu in interpreting the knock retard value.

So something isn't adding up. The knock retard does not account for the retarded ignition timing I'm getting and at high RPMs having advance in the single digits doesn't seem correct and I get little pull at high RPM as a result.

So what other inputs does the ECU use in determining whether to retard ignition timing other than the standard stuff of throttle position, RPM, MAP, and inlet air temp? Those parameters are typically static tables in the ECU. All these readings look perfectly fine on my OBD scanners.

I thought for sure I was getting timing retard as a result of the ECU picking up noise on the knock sensor, but the latest measurement seems to indicate this is not so. What else causes the ECU to retard timing?

Knut

 

[ksgrimsr]

More data

Below is some more data on the basic logged engine parameters during some test pulls. This chart has a lot of data on it and some of the colors are pretty similar but you should be able to make it out. This data does not include the knock retard or knock sensor voltage that I reported previously since that is only available from the Tech-1 which doesn't really do logging. Also, because I'm collecting too many channels the update rate is pretty slow and as a result you see the same value being repeated a lot and the time resolution is poor. Some of the samples might fall in the shift points and look funny due to the time resolution coarseness.

At about 8 seconds before I start the pull you see the advance is around 30 degrees and then I put the hammer down a little before 10 seconds. At about 12 seconds the boost is 1.75 bar, TPS is at 100%, RPM is 5000 and IAT is 35 C. Everything looks sweet except the timing drops down to about 8.

Inadequate fuel pressure has been mentioned a couple times. If low fuel pressure doesn't result in knock (no knock or knock retard recorded by Tech-1) what input does the ECU use to know the fuel pressure is low in order to know to retard the timing? I have O2 sensor readings as well for the pulls in the chart below (not included on chart since it would clutter it even worse), and O2 sensor readings do not indicate a lean condition (both banks record voltage during wide-open throttle in the 0.85V to 0.9V range which is slightly rich).

Thanks for the help guys.

Knut

 

[ksgrimsr]

I'm not sure what banner you are referring to that's covering up the legend and the chart in the posting looks fine to me, but the image below is just the legend to help clarify. Unfortunately, there are 3 blue colors Excel decided to choose for the chart and I didn't bother changing the colors to better distinguish them, but from context it's easy to see which is which in the chart.

The power reduction happened between laps 2 and 3 of the second session of a track day a while back, so there is not a clear correlation of the loss and something that was serviced on the car.

I'm presuming that the timing values that I'm measuring are quite retarded since I'm not used to such low advance values on other cars and it feels like retarded timing since the pull at higher RPM's is poor, but I have to admit that I don't have a baseline on the 918 engine to compare against to even know whether the timing values are indeed retarded compared with what they should be. Does someone have timing values for their V8 under high-output conditions and can confirm that my values are indeed different than they should be?

Knut

 

[ksgrimsr]

Thanks for chiming in.

Unfortunately the chart I posted has 3 blue lines on it which confuses things a bit. My IAT is the flat blue line that starts out at 35C and slowly rises a couple degrees to a little under 40C in the chart during the pull, so my IAT looks pretty nice and the intercoolers are working well.

So my timing looks reasonable to you? Unfortunately I don't have a baseline to compare against and with poor power at high RPM it felt like retarded timing so it's one of the things I checked (after chekcing boost, etc). Does anyone have a baseline they can post for what is considered normal on a well-running car? What PC based OBD-II reader are you using for your V8 that supports the Lotus specific values?

Thanks for the help.

Knut

 

[ksgrimsr]

Looks like our messages crossed each other.

I have air/water intercoolers on my V8 and although the engine was up to temp I hadn't done a lot of pulls yet when I logged the data in the chart so the coolant for the intercoolers was nice and cool giving me a pretty nice IAT. Even at the track when things are all warmed up and I've been flogging it for 20 minutes the IAT usually holds around 60C. There is a writeup on my intercooler setup back in the archives.

Knut

 

[ksgrimsr]

Here are two PDF's of my stock ECU with intercoolers.

Thanks for some data for calibration. Your charts are a little tough to view as well (though not much worse than mine). In your second chart it seems like it's easiest to see -- to be sure I'm interpreting correctly, at T=2472 you go hammer down (TPS goes to 100 and boost goes to 50) and your advance drops to about 10? Am I reading that right?

Based on your own measurements and looking at mine, is the advance (retard) I'm seeing basically the expected values?

Knut

 

[ksgrimsr]

Like I said previously, your logged timing is as correct as OBD2 scan rate will report. timing can go to 6* with boost and elevated IAT. there is a lot of performance left on the table, which can be captured if you can control IAT, the boost and timing curves.

So in the chart I attached my IAT's are under 40C (under 100F) and they won't get cooler than that without refrigeration. Just to be clear I understand your inputs, the timing advance I'm seeing in the chart is entirely consistent or are you saying it would be consistent for high IAT's (which I do not have)?

Thanks for your help and insights.

Knut

 

[ksgrimsr]

Problem solved

I addressed my performance issue and wanted to share the findings with the group in case someone else encounters similar symptoms.

My symptoms have been that I get really crappy performance at higher RPMs which is the only place our low displacement turbocharged motors actually have any performance to start with. With the way it petered out at higher RPMs it felt like I was getting no timing advance, and you all know that I have been hunting down all the possible ways in which I could be getting timing retard.

Well, I finally had a secondary failure that gave me the clue I needed to home in on the true culprit. I developed a coolant leak that I fixed a couple days ago. The leak was caused by a coolant hose getting compromised due to being heated by a nearby pipe.

The nearby pipe was the plumbing for the air injection pump into the exhaust heads. This pipe should not get hot since it has ambient air flowing into the exhaust manifolds and not flow going the other way. But this pipe was clearly pretty singed and it used to be powdercoated and now it was burned to a dull metal grey, and in the process it compromised a nearby coolant hose.

Aha! There is exhaust gas flowing through this pipe when there shouldn't be any! That can only be caused by a pressure differential between the two exhaust manifolds resulting in gasses flowing through the pipe. So…. I have a plugged up exhaust on one side (or both) restricting exhaust gasses from exiting the manifolds and giving me pressures that causes a flow through the air injection pipe. Eureka!

So I pulled the first catalytic converter off the car and peered inside… And what did I find? Looks perfectly pristine and there is absolutely nothing wrong with it. Sigh…

So I pulled the second catalytic converter off the car and peered inside… And what did I find? Complete crap! The first picture below is the exit side of the catalytic converter and you can see that the honeycomb in not only bulging out the exit, but it is turned sideways. The second picture below is a picture of my borescope looking at the entrance side of the converter and it looks like Armageddon. I think we found my problem!

These cats are the more rugged spiral-wound sports cats and the one that failed lasted a total of one and a half track days, which is why I didn't pursue looking at the cats right away since they are brand new and they are of the ruggedized variety. I still have my factory cats and they are in fine shape and I'll be putting those on whenever I have to go through DEQ, but I'll be running hollowed cats at the track from here on and simply do some swapping around as needed. I'm not sure I'll have better success with any other cats so I might just be destined to do some swapping.

And what about my ECU readings dropping out while I was data logging? My plugs were not looking great and at high pressures and poor breathing of the engine the electrical noise generated by the spark was so bad that it was interfering with the bluetooth communication between the OBD-II dongle and my data acquisition receiver. Let the engine breathe better and put fresh plugs in and I'm getting nice clean readings again.

Knut

 

[ksgrimsr]

The catalytic converter material in the spiral wound sports cat does indeed seem quite durable and it was a real pain to extract it from within the cat. It is not at all brittle and cannot be broken up.

The material is like tiny corrugated steel that is wound up in a spool (hence spiral wound) creating a disc, and there are two of these disc spiral spools in the cats that I bought. Each spool has a spike driven through it to keep it from un-spooling (you can see the holes in some of the un-spooled ribbon in the picture) and give it some integrity and each spool is captured in the corresponding bulge in the catalytic converter housing in the picture.

My failure seemed to be that the spools were not captured well in the housing so they shifted/rotated/smashed, etc.

Regarding the post-cat O2 sensor that Dave mentioned, the O2 readings were perfectly fine since whatever little gas did indeed pass through the wrecked catalyst was getting catalytic reaction resulting in the O2 readings being reduced and delayed on the exit side of the cat just as it's supposed to be. The sensor didn't distinguish that the volume of flow is inconsequential, only that the oxygen content of the exit side gasses were as expected.

Knut

 

[ksgrimsr]

Have been enjoying some great track time with my car this summer with the hollow cats. With a simple spacer on the rear O2 sensors I don't even get a CEL indication and the ECU is perfectly happy.

With the hollow cats I do get the added benefit of keeping some of my fellow drivers on the track from riding my tail with the flames coming out the exhaust when shifting at red-line at max boost, but that's all fun.

Had another exhaust failure at the track a couple days ago. What can possibly fail when running hollow cats???

Well, I had my exhaust shear off at the junction to my hollow cat and I have signs of cracking at the muffler. Not a good idea to keep running that way and I immediately eased off and limped home with the change in engine tone. Burping fireballs into the engine compartment from the exhaust break is a great way to test the effectiveness of your fire suit.

There does not appear to be any compliance in the exhaust system despite the length of the system and the resulting lever arm it creates. I'll be welding in a few flex couplings to provide some forgiveness to vibration and flexing, and I'll post a couple pics when I have the mods done.

With the original exhaust, I don't see how it would possibly ever actually endure unless the car was used exclusively for Sunday cruising. What's the point if you don't actually get to exercise it properly??!!

Knut