Rich spikes causing engine "hiccups" after ECU swap

[jaqattack02]

I replaced my Nistuned 84T ECU this past weekend with an 87T ECU with a new Nistune board. After replacing it we more or less had to retune the car as almost nothing was able to easily port over from my old tune, I guess due to address file differences. We got that handled without much trouble, my maps aren't terribly far off a stock tune. It runs great for the most part, good AFRs in boost, pulls smoothly, etc. The issue I'm having is the car will "hiccup" from time to time. We were watching AFRs and apparently it is randomly spiking really rich, which makes the car lose a bunch of power for a second. Can't find any obvious reason why. Any ideas on where to start looking? My first suspect would be something in the ECU or tune, as that is the only big thing that changed.

[Matt]

I thought you could copy the fuel/timing maps straight over and then just adjust the K constant...

Anyway take a log with the injection time and AFRs (from wideband) and see if the injection time is spiking at all (or the MAF or TP) in the log file

[jaqattack02]

I thought you could copy the fuel/timing maps straight over and then just adjust the K constant...

Anyway take a log with the injection time and AFRs (from wideband) and see if the injection time is spiking at all (or the MAF or TP) in the log file

When I copied them it messed up the TP scale across the top. Changed it to 63 all the way across.

I'll take a log and check that that stuff, see what it looks like.

Someone in another forum suggested it might be a misfire as well, so I'm going to take a look at that possibility as well. The only other thing that changed recently was a distributor swap to eliminate the possibility that the CAS was causing issues. I'm going to try swapping that back to the old one.

[Matt]

You need to open two copies of Nistune and use copy/paste to copy the values

You cannot load the filefrom one type of ECU into a different ECU directly as the definitions change between them (maps located in different parts of the file)

[jaqattack02]

I did some logging and below is a screenshot. You can see the dip in the AFR where the stumble happens, and right before it the injector timing spikes.

[jaqattack02]

I'm also getting stuttering in boost now, which it didn't do that even the other day after installing the ECU. Looking like the injector timing is all over the place for that.

[jaqattack02]

I did what you said and opened 2 copies of Nistune and was able to get all of the relevant tables and info copied from my old tune into a fresh stock 87T tune. Car definitely runs better. Idle is smoother. Though it's not fixed, the two issues I was having above are still there. If anyone wants to take a look, I've attached my tune. Some key points on the car are 450cc injectors, Z32 MAF setup as blow through, Isky cams, and an S12 intake on a stock TB.

[jaqattack02]

Could this be the cause of it having issues in boost?

[jaqattack02]

Nevermind, going back and reading the tuning guide again answered my question. So that just leaves the issue with the "hiccup" while cruising, if anyone has thoughts on that.

[jaqattack02]

Just as a follow up, I set the "Load (TP) Cut" to 255 across the board and no difference. It still stutters and hesitates in boost, with the Injection Time (LHS) bouncing up and down between 5 and 10 ms. I also swapped my distributor out and I'm still getting the little hiccups while cruising, so it isn't a CAS issue. I'm really at a loss here as to what the issue could be and could use some input from someone more knowledgeable.

[jaqattack02]

What does the "Default TP/RPM Scales" flag do?

[Matt]

Sorry for the delay. I'm still to find some time to run an ECU on the bench with your tune to repeat the issue here. Friday got crazy so I'll have a look on Monday

In the Z31 I dont think the TP load limit table was used in some models which is why it doesnt have any change

The spikes are strange and look like some kind of cut so I'll run on the bench to repeat here. Do you have the log file for this also you can post here?

The default RPM/TP scales should not normally be changed. There are two sets of scales (TP,RPM and VQ) in the Z31/R31 ECUs. This is selectable by these parameters. Nissan ran two ROM chip in these ECUs one larger masked ROM and a smaller PROM which formed the memory area in the ECU

The PROMs were cheaper and contained most of the maps and configuration parameters in the ECU. This feedback flag parameter was used to switch between two sets of scales depending on the final vehicle configuration.

These days we can adjust all the maps with ease via USB so you only see the main maps displayed in Nistune (the other ones are in the background and only used if you untick that box)

[jaqattack02]

Here's the latest version of the tune along with the last few logs I ran.

I'm just worried this ECU is having some kind issues with the injector drivers or something. That would be rather upsetting as I just got it to replace the one that was randomly cutting the car off.

[jaqattack02]

Here's the tune, hit the 3 attachment limit on the last post.

[Matt]

I've run this on the bench today. The spiking you are seeing with the injector time is the changing between batch/sequential injector modes

If you hold the RPMs right near the switch over point then it will go between these two modes. When it does this the injectors fire for half the time, but fire twice as often. There are only two injector drivers in the ECU so I think those are fine

I'm not seeing your AFRs in the logs here to see if that is causing an external effect (it shouldn't if all injectors are flowing the same and latency is correct). Should not be affecting the operation of the vehicle but see if your AFRs hiccup in the log file at this point