Hi all, long time reader, new poster.

I have an LS1 swap in my 74 Datsun 260z. Motor is a stock LS1 (M6 transmission) with shorty headers. The exhaust was 2 2.5" run into a single 3" pipe. I took it out of town be tuned on HPT by a very experienced LS tuner shop and the car has been running great ever since I finished it. Please see the 1st graph attached for reference.

Recently however I've run into a couple issues.

I have installed long tube headers onto the car and had a shop weld up a full custom stainless 3" exhaust.

Thinking I needed a tune to get my AFRs dialed in I took it to a local dyno shop (very reputable local shop but most of their experience is in Honda tuning). Please see the 2nd attached graph for reference. The first numbers were using the same map as my shorty tune, you can see the long tubes seem to lean everything out (as one might expect?). The tuner added a lot of fuel and the car seemed to make best power at seemingly somewhere in 10:1 - 11.5:1 AFR. The engine seems to be making good power so I feel like its running pretty healthy. However, this is far richer than anything I've seen online and has me concerned. Is there anything they could have missed that could lead to such numbers?

I've also noticed the car stumbles a bit when driving on the freeway. It only really happens when you give it throttle while in 5th or 6th gear in the 1200-1600 rpm range. Outside this range it seems to run great. I'm also getting the p1153 codes. I'm thinking the longtubes leaned everything out and it just needs a little more tuning to make this right.

I already plan to bring the car back in for more tuning. I would like some feedback on my issues to let me know if I'm thinking about this the right way and am not missing anything. Ultimately I trust the shop to do a good job and make everything right for me but I'd like to be able to steer them in the right direction if necessary. Any thoughts or advice would be awesome. Thanks!

 

Is the car running a MAF? Stock cam?

 

Yes on both.

 

11.5 to 1 is superchaged territory for afr , 10 to 1 is just plain rich for any application stock ls shoot for 12.5-12.8 at wot , some even go 13 to 1 at wot

 

Where was the wide band mounted?

 

If this is closed loop and rich (your running / stumble
complaint) then this may be header thermal vs O2
sensor heat-needs, causing false trimming. Shorties
ought to not do this, long tubes almost always do.

If you need that much WOT fueling to make best
power then you probably have too much spark
advance. But your Honda tuner may not know about
stuff like cat overtemp protection, which lays down
that kind of enrichment whenever you get on it for
more than a couple of seconds (black smoke at WOT)
even if you lean out the PE and EQ tables. He ought
to be looking at commanded AFR and the various
components of it (richest is used, you want to know
what is controlling it and why).

 

Thanks for the replys it definitely confirmed to me that something is not quite right with that tune.

The new longtubes connect to a 3" pipe which Y into a 2-1 merge connector and have 1 single 3" pipe going out the back of the car. The wideband is mounted on one of the initial pipe sections up stream of the merge.


I briefly read about cat overtemp protection. My car obviously has never had any cats so I hoped that the shop that tuned the car originally had this already adjusted close to where it needs to be. If this is not the case, or these parameters need to be re-adjusted with the long tubes then I can ask them to look into it.

I found a new issue with the car I had no seen before as well. The car will start up cold just fine but after driving it just a little but it will stumble and the idle will surge quite a lot. After doing this a couple times it will run as before until I turn it off to get pretty cold.

Since the tune is seemingly so far off at this point I am thinking the best thing to do now is get a mail tune to set a good baseline and get the ECU setup the way it should. Once that's done I can bring the car back to the shop for a few pulls to see if its worth to make any adjustments. Any more thoughts?

 

I would tell the Honda shop I wasn't happy with the tune and ask them to flash the old one back in. Being that its a stock cam and you're running a MAF, it shouldn't be far off, if off at all. As long as you didn't change anything in front of the MAF on the intake tract.