hello,

I had my car dyno tuned at a local speed shop. The car runs well between 14.6 and 15.3 at part throttle. WOT seems good as well beteem 12.2 and 13.0. MY issue is idle or anytime i'm off the gas, it goes very lean on my AEM WB gauge 18++. This always happens within seconds of cold or warm start it will start around 15 then quickly decay. I did a few datalogs and it seems to be an open loop tune. The BLMs stay steady on 128. A member on here was nice enough to look at my logs and he added more fuel in MAF table 1. I dont trust myself to change the tune, I am still having this issue. I'm going to try to attach a datalog to this post. This is a engine with only a 650 miles on it but I had to replace the valve guides 130 miles ago, i'm wondering if the guides were ruined from heat do to his lean idle so I want to avoid that happening again. If it's not the tune maybe I have a vacuum leak? bad MAF? Bad O2 sensor(heard stock O2 wont effect open loop tune?) Thanks for any advice or help.... doesn't seem to let me attach files of logs or bin.

 

Odds are that it is an exhaust leak. At 18:1++ AFR the engine wouldn't be running.

RBob.

 

Thanks RBob, I managed to attach a few files. I'll check for an exaust leak but had new exaust put on before and after this issue. I have also noticed my headers glow at idle if I let it run for a while with this tune. Also the plugs do get white grit on them think from being lean and the engine will begin to shake if left at idle for over 5 mins.

update, checked exaust and header and collector bolts are tight with no seen leaks.

 

https://www.thirdgen.org/forums/diy-...s-lean-pt.html
could this be my issue?
my NB 02 is also indicating lean 100% of the time at idle.

 

Changed my NB O2 and no difference, went lean at idle 18++. could my lean idle be to a vacuum leak at the injector O rings? I sprayed starter fliud in the injectors and WBo2 read richer?? Anyone??

 

Thats an interesting observation. try spraying around the intake as well looking for vacuum leaks.

 

yeah, had my wife watching the WB O2. It went lean as always after start 18+. She told me it was going 12.4-13.3 when I sprayed the starter fluid on the injectors. I ran out of starter fluid but am thinking possible bad injector O rings? I'll have to get more starter fluid to confirm.

 

https://www.thirdgen.org/forums/tpi/...ctor-swap.html

I did a search and found this post. I'm running Ford 30 LB injectors and seems that the Ford injector O rings are smaller then the GM injector O rings. If I confirm the AFR gets better spraying the injectors again with starter fluid it looks like I'll be changing the O rings.

Vader
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Join Date: Jan 2000
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Classifieds Rating: (0) Re: What injectors can I use for my '89 T/A 5.7?

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Ahhh, you're just lucky (or really paid attention when assembling them). The Ford O rings are just a tad smaller cross section, and sometimes don't seal. If it's on the fuel rail end, you'll know it right away. If it's on the intake end, you might not know it until you start chasing a "mysterious" vacuum leak or mixture problem.

Other than that, I haven't heard anything negative about them. Be careful to select the proper flow ratings, since GM rates flow at 3 BAR (like the rest of the EFI world) and Ford rates flow at their normal regulated line pressure of 36-38 PSIG, and sometimes at 48 or even 55 PSIG.

The other factor to consider is the design of the injectors. You need saturated injectors, not peak-and-hold (foldback) injectors. Typical solenoid coil resistance of a saturated injector is in the range of 15-17 ohms, whereas a P&H injector is closer to 2-4 ohms.

 

Sounds like you found an/the issue. If still running closed loop the BLM value should have increased to make up for the air leak. If you have a log of warmed up closed loop op at idle check the BLM.

RBob.

 

Pretty sure its an open loop tune

 

That may be the issue...the amount of fuel added in MAF table 1 showed just a little improvement, and then still went lean. I would have expected it to really richen up the system. Swap out new o-rings and see if that changes the idle air fuel. I'd expect it to be too rich now with the 5F tune

 

After some data logging it was found that the O2 sensor, new but non heated, was going cold at times in idle. This cold O2 read 4 mv at times, which is interpreted as lean. This helped to cause a rough and lean idle. The O2 is installed down the pipe in the header.

The second issue was the Maf was under reporting the air flow by 25% across the range of reading. This under reporting also lowered the amount of fuel being delivered, which was causing other issues, knock and poor performance.