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That test looks a lot like the test on my '95, but I suspected a damaged injector wire on that (since cylinder 1 had blue painter's tape on it, and underneath was an exposed wire that had corroded). I haven't fixed that yet and re-run the test, but if it looks the same and your problem is a bad intake manifold gasket, welp, guess I'm doing an intake manifold gasket too...
Similar looking test huh? Thats interesting. Maybe we're on to a common problem. One thing I'd like to note is I not only performed this test at idle like the instructions say, I also performed the test at higher rpm like 1000 and 1500. I discovered that the percentage difference between the weakest and strongest cylinders was narrower at higher rpm's. That made me think vacuum leak since vacuum leaks usually are more pronounced at idle, and my BLM's are closer bank to bank at higher rpm's.
In addition to the possibility I messed up the intake gasket (which I plan to do over for good measure either way), I also thought maybe a problem with the PCV system or the throttle body or both.
I had pulled the intake to clean the sludge from the lifter valley. When I had it off I also removed the baffle from the underside of the intake to clean it all out. This baffle acts as a channel so the PCV supply air is pulled through vent holes in the front part of the baffle (see pic below). I thought maybe I somehow did not get things cleaned up enough and maybe that baffle is leaking around the mounting surfaces causing lean conditions towards the front of the engine. Also, on the passenger side valve cover is the tube where the PCV system pulls metered air in through the throttle body fitting. At this hose, when I pull it off of the valve cover I dont feel any air moving through it. So where then, is the air that the PCV is pulling being replaced from? Weird to me. I can can blow through the the hose into the valve cover and into the TB and there's no restrictions. I'm gonna plug the PCV system off entirely, clear the PCM, strart up and relearn to see if the condition changes.
On the throttle body idea; The shaft that the blades are attached has some play in it. I'm not sure how much play is tolerable if any, but its a tad loose. Its little looser than the one on the vette. Camaro has 126k, Vette 60K. Maybe its leaking through the throttle body shaft and that's messing things up. l think most of the stress on the TB shaft is on the drivers side where the cable is hooked up, so maybe that could explain the weak cylinders closer to the front, and more prevalent on the drivers side.
Note: your 95 baffle may be different from the 94. I know the exposed pcv line routing is different between 94 and 95.
Similar looking test huh? Thats interesting. Maybe we're on to a common problem. One thing I'd like to note is I not only performed this test at idle like the instructions say, I also performed the test at higher rpm like 1000 and 1500. I discovered that the percentage difference between the weakest and strongest cylinders was narrower at higher rpm's. That made me think vacuum leak since vacuum leaks usually are more pronounced at idle, and my BLM's are closer bank to bank at higher rpm's.
This is because you poisoned the test results. Those instructions are not for show; the test is only designed to be done at idle, and can only provide useful data at hot idle. It actually has a lockout to prevent you from starting the test at a TPS value over 0%. Clearly you bypassed this.
Last edited by Nomake Wan; Jun 3, 2021 at 08:51 AM.
[QUOTE=Nomake Wan;1603541510 Clearly you bypassed this.[/QUOTE]
It was easy to do. Just set the idle higher in the control panel, don't close the control panel but minimize it which keeps your instruction active, then go do the test. Maybe my data is skewed buy I can say this, it evaluates in the same manner. Matter a fact, as it cuts the cylinders one be one, you can hear the difference much more at the higher rpm setting. But I wont argue whether I got good info or not out of doing this. I saw the instructions to do the test at idle. But, is it possible that the purpose of doing the test at idle is to be picky about reporting efficiency differences because the program recognizes deficiencies at a more minute level at lower rpm's? If so then the test still works at higher rpm's, it only can't recognize smaller differences as well as compared to lower rpm's.
On the throttle body idea, I got lucky a while back and got a Holley aftermarket TB at the junkyard for a steal compared to what it costs new. It's in great shape and I just checked the throttle shaft play and it is dead zero, no up and down slack. I just wanted to compare that one to the stock one which is sloppy. I'm not crazy about putting this Holley TB on the car to do diagnostic because I know the larger bores will change other things and then I might be really chasing my tail. I wonder if theres a way to fix the loose throttle shaft. Maybe a bushing kit?
Maybe my data is skewed buy I can say this, it evaluates in the same manner. Matter a fact, as it cuts the cylinders one be one, you can hear the difference much more at the higher rpm setting. But I wont argue whether I got good info or not out of doing this. I saw the instructions to do the test at idle. But, is it possible that the purpose of doing the test at idle is to be picky about reporting efficiency differences because the program recognizes deficiencies at a more minute level at lower rpm's? If so then the test still works at higher rpm's, it only can't recognize smaller differences as well as compared to lower rpm's.
The programming of the test itself wasn't designed to handle the difference in cylinder efficiency at higher RPMs. It's only 'calibrated' for the idle characteristics of the LTx. That's why I mentioned it's 'poisoning' the results to do it at higher RPMs. So yes, you won't actually get useful data out of the program itself. Nothing stopping you from using the Controls section to mess with the injectors one by one and do a test with a vacuum gauge yourself though.
About 130k on my 95, I have no reason to believe either has ever been off. The throttle blade shaft is quite snug.
When you checked the TB shaft for play, did you first move it up off of the throttle stop screw? Mine seems tight when its resting against the screw. But it moves up and down when you take the tension off the throttle stop.
I would be very reluctant to use anything with (real) Copper near or on aluminum. I realize that Copper gasket makers have been around for ever it is really designed for use on ferrous metals in the older days. Be sure whatever you are using is designed for use with Aluminum heads or Block.
A (Champion Brand) graphite based anti-seize is used on my spark plugs. Since my C4 came with aluminum heads whenever you put Steel spark plugs in it is very important to use anti-seize. The Steel against the Aluminum will make the removal more difficult that it has to be. Aluminum heads and Steel Spark Plugs is a recipe for trouble. Galling occurs between these two metals and they become virtually impossible to remove without taking the threads out with it. "Galling" is what occurs and I found a explanation on Wikipedia. Galling is a form of wear caused by adhesion between sliding surfaces. ... For example, aluminum is a metal that will gall very easily, whereas annealed (softened) steel is slightly more resistant to galling. Steel that is fully hardened is very resistant to galling.
The rest of the engine gets the standard thick graphite anti-seize on every steel bolt going into aluminum
Many years ago I saw a neighbor paint a Brand New Sears 12' Aluminum boat with "Bottom Paint" that had Copper in it. Copper is added to Marine "Bottom Paint" to help keep the barnacles and growth to a minimum as it is toxic to them.
Literally, the next morning you could push your fingers through the painted areas. Copper on Aluminum is a BIG no-no in the Marine world.
Thank you Both John Dirks Jr and Nomake Wan for theknowledge you have shared here on this post! I am still in the dark ages with my Snap On MT2500 but plan on making the change to using a software like you suggest. After following this post I now am more confident I will be getting the best software. EEHack and a cable will soon be in my bag of tricks! Thanks again for the education and suggestions. Do I do anything pother than order a OBD 1 cable and Download EEHACK?
One question, on the Videos showing the data while the car is idling and at 1000 rpm both show the same Knock Count of 4578 and that does not change while the engine is running?
The Oxygen sensors in the your Corvette John look to me like they are staying on the high side in the averaging. O2's were designed for a 24 month useful life starting from the minute it is installed. Heated O2's are now able to last twice as long as the unheated type the early C4's used. I would seriously look at them as when a O2 starts to fail the signal strength weakens or narrows, instead of going from .9 to .1 they start going between (for example) .3 to .7 and this has an effect on your Engine by slower data coming to it that is no longer as accurate as it needs to be. The oxygen sensor will frequently fail on the rich side to prevent damage to your engine. For the price they are the best way to get better economy and performance. I was taught to replace them as a pair if you need two for your Corvette. I like just having a single O2 but have debated upgrading the O2 to a Heated Style which allows the engine to go into Closed Loop faster. Believe it or not some old non-heated O2's will actually switch back to open loop as they cool down when sitting still, this is why the heated ones is superior.
Do I do anything pother than order a OBD 1 cable and Download EEHACK?
That depends on what your objective is. If you only need datalogging and diagnostics, then yes. If you intend to make adjustments to the tune (or 'calibration' to use GM's term), you will also want Flashhack, TunerPro, and the 94-95 Corvette XDF for TunerPro. Note also that these only apply to the 1994-1995 Corvette and no other C4 Corvette. That includes EEHack (which is named after $EE, the mask used for the PCM on the 94-95 Corvette).
Originally Posted by ctmccloskey
One question, on the Videos showing the data while the car is idling and at 1000 rpm both show the same Knock Count of 4578 and that does not change while the engine is running?
The knock count is an internal counter in the PCM. Any time you start one of our cars, it increments just from the action of the starter. It's unavoidable (unless you completely remove the knock sensors). Raw knock count is not a good measure of knock in a vacuum; it must be correlated with other data to become useful, such as actual knock retard commanded.
Originally Posted by ctmccloskey
The Oxygen sensors in the your Corvette John look to me like they are staying on the high side in the averaging. O2's were designed for a 24 month useful life starting from the minute it is installed. Heated O2's are now able to last twice as long as the unheated type the early C4's used. I would seriously look at them as when a O2 starts to fail the signal strength weakens or narrows, instead of going from .9 to .1 they start going between (for example) .3 to .7 and this has an effect on your Engine by slower data coming to it that is no longer as accurate as it needs to be. The oxygen sensor will frequently fail on the rich side to prevent damage to your engine. For the price they are the best way to get better economy and performance. I was taught to replace them as a pair if you need two for your Corvette. I like just having a single O2 but have debated upgrading the O2 to a Heated Style which allows the engine to go into Closed Loop faster. Believe it or not some old non-heated O2's will actually switch back to open loop as they cool down when sitting still, this is why the heated ones is superior.
To be perfectly clear to the OP...
1. Your Corvette has 3 O2 sensors, all three are the more advanced heated type.
2. You only need to replace the "front" two. The third behind the catalytic converter was experimental, and has no bearing on the operation of your vehicle.
3. It's usually possible to tell when the sensors are starting to go out because they won't fail simultaneously. One or the other will start reading wonky values, which will show up in EEHack datalogs.
4. If you've never replaced them and do not know the history of the car, they are cheap insurance to replace anyway.
5. When replacing the sensors, note that the connectors have a plastic clip that fits into a metal bracket on the car. It is critical to clip them in. This prevents the wiring harness from contacting the hot exhaust or engine and melting through, which is a serious concern.
Hope that helps.
Last edited by Nomake Wan; Jun 3, 2021 at 02:42 PM.
The 94 Camaro z28 engine that is the subject I started this thread over only had two o2 sensors. One on each side of the y-pipe upstream of the cat. None behind the cat.
If anyone watching this thread cares to know, this is the cable I got and it's working well. I use this with EEHack, Flashhack and TunerProRT which are all free programs although there is option to donate to the software writer. These programs are good for 94 and 95 LT1 engines and PCM systems only in Corvette , Camaro, Firebird, Caddy Fleetwood, Chevy Caprice and Buick Roadmaster.
I stand corrected as Nomake Wan says below. Sorry for the confusion.
If anyone watching this thread cares to know, this is the cable I got and it's working well. I use this with EEHack, Flashhack and TunerProRT which are all free programs although there is option to donate to the software writer. These programs are good for 94 and 95 LT1 engines and PCM systems only in Corvette, Camaro, Firebird, Caddy Fleetwood, Chevy Caprice and Buick Roadmaster.
CAUTION TO CORVETTE OWNERS: This cable WILL NOT WORK for the 1994-1995 Corvette. The Corvette had already moved to the 16-pin ALDL connector in 1994, whereas the F-Body (Camaro) had not.
CAUTION TO CORVETTE OWNERS: This cable WILL NOT WORK for the 1994-1995 Corvette. The Corvette had already moved to the 16-pin ALDL connector in 1994, whereas the F-Body (Camaro) had not.
I just measured the aftermarket Holley TB I previously nabbed from the junkyard. It’s actually a 52mm, kind of Holleys version of replacement part for the stock 48mm. It might be worth a try installing it to fix my loose throttle shaft condition and see if it corrects the bank 1 lean condition. I paid $25 for it and they list new for $459. It’s in great condition with zero play in the throttle shaft.
Im also going to correct the injector flow rate in the tune since it had been set by the tuner a tad high. So obviously that contributes to the overall lean condition. However it does not explain being more lean on bank one. Maybe the loose throttle shaft does since the leak would be on the bank 1 side of things.
My current tune is set with the injector flow rate at 25.37 (that’s what the tuner did)
My replacement injectors are rated by the supplier at 24lbs at 43psi.
My idle fuel pressure is 39 psi. So, as per calculation, to get my fuel trims centered I need to reduce the flow rate in the tune to 22.86. I’ll try this and see how the data stream changes. I know it won’t fix the difference between banks but it should move both sides closer to center and maybe give me a better idea of what is happening.
I think I got it dialed in. I closed the throttle blades to just above full closed, slotted the TPS and set voltage at .65. I adjusted the injector flow rate in the bin a few times until I found that dead on 24lbs (23.98) gets me on center in the trim range.
I know I can data log with EEHack but I wanted to make this also viewable to persons who may not have the program. So I screenshot the data to a YouTube video. I set the trim to percentage view also. Idle was set at 800 during this sample and I opened the the throttle a few times as well.
Here’s the link. Anyone see anything too out of line here? Remember it’s just a no load run. The car as a whole is not drivable at the moment.
Looks really good at a glance, congrats on doing your own tuning! You can actually tune the fuel tables a little more once you get it drivable using a tool by the same author, Trimalyzer. So if the tables are off in a particular BLM cell while driving, that can be corrected. Then again it's also something that should be corrected by a mail-in tuner, since they should be asking you to drive around and datalog and provide them with the log so they can do the adjustment......but if your tuner is a one-and-done sort of thing, well, no worries.
The problem with a youtube video of the main screen is there's a ton more information that you can't see. I understand wanting more people to be able to look at it, but the people who are going to be able to help you either already have EEHack or are familiar with using CSV datalogs to analyze data. Fortunately, EEHack provides both options. I personally prefer EEHack's proprietary log since I can pop it into my laptop and look at it as if it were my own car. But if you want to share a version of the log that'll be viewable and analyzable by anyone too, no problem! Click the 'Main' tab in EEhack, then click the "Export CSV" button on the right side. This will export a CSV file that can be analyzed by anyone, not just by people who use EEHack. Additionally, Trimalyzer uses CSVs, so if you decide to start trying your hand at tuning fuel, you'll need that anyway!
Thanks for the data logging tips. I’m sure I’ll be recording and sharing them in the future.
I’ve have the front clip off the car which has made working on it much easier. I now feel good enough about running condition of the engine to put the front clip back on and begin working on the permanent fuel delivery system.
I also need to teach myself how to solder wiring properly. The harness is basically a rats nest now. Once the clip is on, I can decide the home for the components, mount them, trim down the wiring and solder up.
On the desired idle setting it’s currently at 550. I’d like to have it at 750. Where in TunerPro can I make that change? I haven’t seen it yet.
I forgot to do another cylinder strength test after the last adjustments but l will do it and post back.
I’m not sure but I think maybe the throttle blade adjustment was a big help. Before, when the engine was running really rough I had opened the throttle blades with the stop screw to try and increase idle which was a mistake. That basically causes a vacuum leak since IAC is controls idle speed anyway. So I closed them back up as far as I could without risk of binding the blades against the throttle bores. In effect, completely closed and handing all idle air supplies to come through the IAC. On second thought maybe I’m wrong about the open throttle blades causing a vacuum leak. After all, a true vacuum leak would be un-metered air bypassing the MAF.
I may still have a small vacuum leak at the throttle blade shaft and l still plan to redo the intake gasket. I have genuine GM intake gasket on the way and complete TB gasket set too. That 52mm Holley TB I have is sweet, but I may not need it after all.
