What do the spark plugs look like? Any signs of the cylinder with the misfire burning oil? Any that look significantly different than the others? Blocked off the brake booster hose yet?
What do the spark plugs look like? Any signs of the cylinder with the misfire burning oil? Any that look significantly different than the others? Blocked off the brake booster hose yet?
I don't think it's a tune problem at all. In fact, it's smart to start off with the factory tune like I provided you. Who knows what clownery went on with the modified tune. The number of hacked tunes from "professionals" is something I wouldn't have expected until I learned a bit about this stuff.
I never heard that. Either way, I need to use the stock tune, because if I need to make any changes down the road, I'll need an unlocked ECM.Originally Posted by SiriusC1024
Sorry I have not got back on this. On the test it is performed with the engine not running. With these fuel injectors they were SOOOO prone to failure it is ALWAYS one of my first tests. Let me get the actual procedure out of SI or ProDemand. Give me a minute.
All the spark plugs look good and similar. The misfire plug looks normal. It's not oily, saturated, or black. I plugged the brake booster port on the plenum, but it didn't change anything. I reinstalled the brake booster hose, fired it up, then removed it, while it was running, and it made a loud suction noise and shut off. Once I reinstalled it, it fired back up, so it seems to be working (unsure question mark).
Thanks bud. I checked HPT though, and it doesn't have an injector balance test option. I don't have another scanner either.
I went ahead and emailed the tuner who wrote my ECM to see if he'll give me a way to access the tune. If he doesn't, I'm going to start from scratch, with Sirius's repo tune, take whatever information you pros are willing to offer, and take my time watching videos on how to properly tune it step by step, until it's good. Another thing I forgot to mention about the cann tune, is it doesn't stop the engine when I turn the ignition off. It doesn't sound like it's dieseling, but the RPM gauge goes negative as it runs for about 5 to 8 seconds, then finally shuts off. Of the ECM's I've tried on my Jeep, it's the only one that does that.
I'm going to take Sirius' advice and check all the mechanicals. One thing that got me thinking though, the passenger side valve cover has a breather port over the #8 cylinder, which is connected to my cold air intake and coincidentally is the same cylinder that's misfiring. I covered the hole, while it was running, but it didn't change anything. Then again, I didn't have another port to install the CAI tube, so I'm not sure if that affected anything.
That hole in the valve cover is the clean air intake side of the PCV system. Now, if there's a stuck open PCV valve on the other valve cover that could be a problem.
I have an extra PCV valve, so I'll change it out and see what happens. I went ahead and removed the tube from the intake, plugged the valve cover hole, and capped the hole on the intake. Here's the log Cann tune after removing CAI breather tube from valve cover and capping it.hpl. When you look at it, if you could explain what you see and whether the numbers are where they should be or not, it would be really helpful, so I know what to look for in the future. Thanks
Which tune were you using in the log you posted after changing IFR to 19.1?
I was using the repo that you sent me. Should I try that tune after the changes to the CAI and replacing the PCV valve?
So here's the log with the Repo tune, a new PCV valve, the clean air port on the valve cover closed, and the same port capped on the CAI Repo tune with fuel pressure at 19.1, CAI capped, clean air port capped, and new PCV valve.hpl.
I know I'm all over the place, and if I'm going too far, stop me, but I just thought about the O2 sensors. Seeing as I removed the EGR system and, technically, it's not a stock Yukon engine, should I have installed aftermarket upstream sensors, or am I good with the new OEM ones? They're welded on, about 7 inches from the collector. I'm running welded solid dual 2.5" straight pipes with Magnaflow offset muffler on each side. I checked for leaks and they're solid. Once again though, when I revved the engine, it would get to about 1600+, then drop to idle and come back up, all while the gas pedal was still pressed down. The stock Yukon and Express tunes are the only ones doing this and I can't figure it out.
OE O2's are what you want.
I think the rpm problem has to do with no speedometer. Yeah. Looks like it's cutting fuel just like the speed limiter would do.
In the future, after fixing the speedo issue, run a longer log and populate more fuel trim cells.
Last edited by SiriusC1024; 06-03-2023 at 12:42 AM.
I've been debating on redoing my dash to add a speedo that connects to the wiring harness, so I'll research it to make sure it'll fix it, before spending that much money. Thanks for all the help. Once I figure out the RPM and misfire issues, I'll post so it hopefully helps others.
The ECU needs to see the speed. A standalone speedometer won't do. Idk which you meant so just saying.
Quick update. I checked for vacuum leaks, and even adjusted the rocker arms, while it was running. I got rid of a slight knock, from piston 8, but it's still misfiring. I'm going to upgrade the spark plug leads coil pack and see if more/better spark might help. I'll post updates.
Latest Update... After staying inside during Florida's hellish heat wave, I finally started working on the Jeep again. I couldn't figure it out so I took it to a local shop. After a couple weeks, the mechanic asked me about the wiring harness and asked if he could get a diagram of the ECU pinout. I did some research and found that Painless Wiring is such a BS company that's full of themselves. Turns out the ECU pinout on their '96 to '99 harnesses only work on a specific ECU part number, used on the '96 and '97 L31 engines, and aside from telling you that you need to order the ECU they recommend, there isn't anything in their manual about the pinout, or how to fix it. The pinout was causing #8 and #1 injectors to fire in the wrong order, causing my misfire. All because I wanted to save some money and use the ECU that I already had. Anyways, sorry for the rant. Correcting the pinout fixed the misfire
, but I still can't rev the engine over 1500 RPMs
. I've attached the tune 1999 Suburban Manual Trans_Sirius_ready_to_write_without_DTCs_and_fuel_rate_at_19.1_10_13_2023.hpt, as well as the log when I ran it today First run with junkyard ECU after fixing misfire.hpl. If anyone knows how to fix the rev issue, I'd appreciate the help.
By the way, in case anyone is using the same wiring harness, and having the same issues, here's the link and explains the pinout issue and how to fix it https://lt1swap.com/painless_96-99_vortec_harness.htm. Too bad Painless couldn't give the heads up to customers, to keep them from wasting money and countless hours.
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