nuclearfishin

Attached are two initial runs I did trying to test the durametric. The first is a pull in 2nd gear and the other is a pull in 3rd gear. I couldn't go to redline because of the length of the private road, but was wondering if any of the numbers here send up any red flags? What other numbers should I log to troubleshoot issues relating to car being down on power? Thanks!

ctony66

You may want to get afr,timing and knock on that list. There must be a reason why the boost is low.

Macster

Ignition timing would be of some value, I think, to see if the DME is dialing back timing to possibly counter detonation.

Couple of things jump out at me.

1) Intake air temperature is quite a bit above ambient. What kind of intake system are you using? I dare say it appears to be a hot air intake system...

2) In the first pull I note boost pressure in bars was up to 0.81 bar then drops off a bit as RPMs climb.

This is my experience with my stock 2003 Turbo. With a stock car the DME only dials in enough boost to satisfy the torque demanded by the driver. If the torque demand can be met with less than max. boost then so bet it. One can see just 0.6 bar (instead of the expected 0.7 bar -- a 996 Turbo mind you). However, in other situations the DME can allow higher boost. I've observed 0.8 bar even 0.9 bar -- at higher elevations.

The second pull developed less boost but I expect the engine was hotter during this second pull. I note the intake air temp was even a bit higher this pull than the first pull.

I guess my question is what boost level and boost curve are you expecting to see?

Also, I note your engine is not stock. Even a stock engine requires good plugs, coils, MAF, and even O2 sensors. As an aside just replacing the sensors on my Turbo -- prompted by a persistent O2 sensor error code and at around 132K miles -- resulted in a marked improvement in the engine's feel.

Modified engines are hard on plugs, and sensors and even MAF's, too.

I do not know the history of your car but ensuring the various items I mentioned above are in tip top shape can only help ensure the engine operates at its peak level.

nuclearfishin

Thanks for the info so far guys, I'll try and add the other data points on my next run.

I have stock airbox running with Champion Motorsport intercoolers. Temps were hot and humid yesterday, in the 90's so that might be why the IAT's were higher.


I'm not sure what the absolute boost level should be, I'm running a GIAC tune and was about 1.5 secs quicker earlier in the year. I haven't changed anything but my times are way off so I'm trying to identify what could be causing this. I do notice boost is down considerably, especially during launch (when it should be overboosting in sport mode).

Good points, I've had my plugs and coils changed less than 3000 miles ago. MAF and O2 sensors are still original (car has 39k miles). What should I be looking for in the durametric data to troubleshoot MAF?

CincyScott

John,
Have most of your problems started with the install of the IPD? I have no working knowledge of them, but many have stated they are a boost leak waiting for a place to happen. Maybe reverse that out and try again? (That may be super hard, not sure)

Also, have you tried a true pressure test on the system? I had a smoke test done on my old car, but not until I put a homemade boost tester and ran it to 25 psi did I find the culprit on my 996tt. I think you did from other pics and vids, so just confirming.

nuclearfishin

I don't believe the IPD is the cause (anymore) as it's been on since last year and the car was running great this spring. I just had the car pressure tested to 22 psi in the shop so I should be good there. Seeing the picture in the other thread of the corroded VGT actuator really makes me wonder. I'm going to check that when I get home today. I normally don't drive the car around in the salt but I do take it out regularly in the winter so maybe I do have a corrosion problem. That might also explain why I'm getting low, inconsistent boost and then all of the sudden it comes on full power like the actuator arm just freed itself. I know that might be a pricey fix but I'm almost hoping it is just so I can solve the problem. Maybe that would be a good excuse to upgrade to 65mm turbos!

Macster

It has been a while since I looked at this but IIRC the intake air temp of my 996 Turbo was very close to ambient air temperature, after a bit of engine running to deal with the heat soak the intake experiences from the hot engine. By way of comparison the intake air temp of my Boxster is always at least 12F or more higher than ambient. The Boxster engine air intake on the side of the body gets some of the hot air from the radiator.

The Turbo's engine air intake being on top of the engine compartment where it gets the coolest air is about as cold a cold air intake system as one could hope for.

So to see the intake air temperature quite a bit above the ambient air temperature is a bit of a red flag to me.

If you are noticing boost is down then as others have already suggested a boost leak has to be a prime suspect.

But other things can cause less than normal boost to be produced.

For instance if the DME is pulling timing the engine will not develop its full power and as a result this limits the amount of boost that will produced.

Just an aside: How fresh is the gasoline? Premium gasoline goes stale and stale premium gasoline may not retain its advertised octane rating. This of course can result in detonation and the DME will dial back timing to save the engine.

(As further aside I experienced stale gasoline in a new Infiniti SUV. No misfires and the engine started and appeared to run ok but the engine felt flat, down on power. Oh the premium fuel was over 6 months old. I drove the vehicle enough to run the tank low and filled the tank with premium fuel and the transformation afterwards was remarkable. The engine was no longer flat, feeling down on power, but was a real power house of an engine.)

Another for instance is if the engine's intake system or exhaust system is compromised, this effects air flow into and out of the engine. This can limit the amount of boost generated.

The only time one of my cars had a MAF go bad -- the Boxster -- there was a CEL and some, well, at least one, error code that pointed to the MAF. Unfortunately I can't recall the error code now. But fortunately I had saved the original MAF. I had replaced the original MAF when I thought it was bad -- based on a CEL with error codes that pointed to a fuel mixture problem -- but the problem proved to be a leaking oil tube filler cap. On a hunch, recalling I had saved the old MAF I swapped out the suspected MAF and installed the old but I hoped still good MAF and thankfully the old MAF was just fine and the new MAF (well, "new" but with around 80K miles on it) was bad.

Absent any error codes that points to the MAF I do not know how to trouble shoot a MAF. It is possible erratic short term fuel trims could be MAF related but that is pretty slim to condemn a pretty expensive piece of hardware.

Modified engines are hard on the MAF. The engine is producing more HP. To do this it must consume more air and with more air more fuel. But in the case of the MAF it is the air that is considered here.

More air means the MAF circuitry has to dial up the electricity increase the voltage that is used to heat the hot film and keep it at its required working temperature (IIRC 200F). How much voltage is required to do this is directly related to how much air is flowing into the engine. But this higher voltage level accelerates the MAF's decline.

O2 sensors as they age generally do not react as quickly to the changing amount of oxygen in the exhaust gases. Or their heating circuit just quits.

The Turbo #1 sensors are wide band. Wide band sensors are used to support more precise control over the fueling. Precise fueling of a turbo-charged engine is to state the obvious critical. If the sensors are on the decline -- and they start declining the moment they are put into service -- and have declined enough this can affect the engine's output and boost.

As I think I mentioned in an earlier post after I had the original sensors in my 2003 Turbo replaced at around 132K miles the engine perked up some. I have had the plugs changed in the engines of both of my cars a number of times and all times I have always been disappointed in that neither engine really exhibited any real improvement in performance after a plug change so I was pleasantly surprised to feel the improvement in the Turbo engine after the sensor change.

nuclearfishin

Thanks Macster, I'll check all of these and also add MAF voltage to my list of data to look at during my next durametric log.

nuclearfishin

Just did a more complete 3rd gear pull. I'm not sure what to look for in the AFR, but I will say the boost pressure looks MUCH better. Any help interpreting this log? Thanks!

nuclearfishin

One thing I noticed on the data above is that timing gets pulled heavily in the middle of the run. The correlation between boost and timing is -.95, so is this a normal amount of timing to get pulled under high boost, or do I have something else going on?