Forums/Z31P/z31-performance-upgrade-forums engine-management/Barely runs, pig rich, after socketed '88NA ECU swap. HELP?!
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Kingman: (2013-07-27 17:30:59)
So I'll start off by saying the truck ran perfectly fine before I broke the '84 NA ECU that was running it, totally my fault. I decided it was a good time to switch to an '88-'89 NA ECU. In a trade it was socketed for Nistune and sent to me. I wired in 6 6.8ohm 10W dropping resistors. Well, I plugged the ECU in and went to fire it up all excited to have my truck running again. It started on the first crank then sputtered and died after 2 seconds. Doing the start-die thing. I can keep it running with my foot on the gas but it's running absolutely pig rich, billowing black smoke and fouling the plugs. Sometimes I'll get lucky and it'll idle at 1-200 RPM if I'm very careful but that's few and far between. I can rev it out but it sounds like a 2-stroke shaking and sputtering. If I induce a massive vacuum leak it'll run at 600 RPM but still billow black smoke. I've probably ruined the oil by now.
I've checked the wiring over and over and over. I've been working on this for 3 or 4 days now.
ECU gives codes 12, 13, 14, 22 - MAF and CHTS are the ones that mean anything. No VSS and the fuel pump isn't wired through the ECU. The common circuit between those two is ECU pin 26 ground so I checked it again and found that the CHTS wiring had a circuit to chassis ground before the ECU, obviously a mistake I had made many many moons ago when building the harness but I thought maybe the old ECU didn't care. I bypassed the harness anyway and ran the MAF and CHTS together straight to ECU pin 26. Didn't change a thing and the codes are still present. At that point I actually took the harness out and went through it, it's fine.
All MAF wiring is correct as is the CHTS wiring. CHTS ohmed perfectly in spec. I checked the diagrams between '84 and '88 to be sure - nothing important is different.
Thinking the wrong EPROM got put in the ECU, I was shipped 2 other ones to try. One didn't work at all (wouldn't read the CAS signal) and the other made it run the same. With the other EPROM that does work the ECU still gives codes 12 and 13.
Tried running with the CHTS unplugged - didn't change a thing.
I tried two different MAFs, one with the adjustable POT and fiddled with it - didn't change a thing.
Tried running with the MAF unplugged - didn't change a. single. thing. You're thinking "well it should have rev limited at 2,200." NOOOPEE, the engine will still rev to the moon with the MAF unplugged!
I've been assured that the ECU "tested fine" before shipping.
I really don't know what else to try other than another ECU. I'll reiterate that it ran fine until the new ECU was put in. Any input is appreciated, I'm running out of borrowed vehicles time! lol!
Augustus Maximus: (2013-07-27 23:38:30)
Swap ECU. Go for an 87na this time.
Kingman: (2013-07-28 00:33:13)
Why '87? I went '88/'89 for the CHTS fail safe and because the NA oxygen sensors are the same incase I wanted to run one.
Augustus Maximus: (2013-07-28 01:07:09)
Same 02 sensor, same CHTS failsafe, but capable of driving lo Z injectors. I'm not a fan of using hi Z ECU to drive lo Z injectors since they require high current to operate properly. It's an improvement over stock if one should run hi Z injectors with an lo Z ECU.
Kingman: (2013-07-28 04:16:53)
So you're saying try a low impedance '87 ECU and keep the dropping resistors I just installed. I've never heard of this problem happening before, its driving me nuts.
Careless: (2013-07-28 07:11:11)
i just socketed a nistune board for RedDemon again due to a wiring issue he had. I plugged it in and realized it works and connects but it runs shit on my car because i have lo z injectors and no resistors for the 88NA board i put the nistune (hi z type ecu). i dont plan on putting resistors because i was just testing the ecu for connection…
but that's not what seems like your problem.
what could be happening in your case is that your injectors are actually hi z, and your previous lo z ECU can run both styles fine without resistors. so now you've probably put resistors across hi z injectors which don't need them.
what year are the INJECTORS from?
G-E: (2013-07-28 07:23:47)
Instead of asking the year, ask him to ohm test them
Careless: (2013-07-28 07:33:01)
you'ze not da boss'a me!
Kingman: (2013-07-28 15:42:39)
Injectors are from an '84. :/
Kingman: (2013-07-28 15:47:05)
2.9-4.3ohms
Kingman: (2013-07-28 16:13:18)
Don't have time because I gotta go help my sister move, but I think I'm going to ohm the dropping resistors. Got a lot of shrink wrap and e tape to get through first but I wonder what the chances of having a bad batch of them are?
G-E: (2013-07-28 21:46:03)
I burned out some resistors when I used a low-imp ecu on the low-imp injectors without removing them… ended up ordering bigger resistors, then found a good deal on large high-imp injectors so that'll solve it anyway
Careless: (2013-07-29 01:51:29)
not likely. also, with sharp voltmeter probs you can poke the heatshrink or wiring without removing all of it.
Augustus Maximus: (2013-07-29 02:58:13)
Nistune uses different latency values for lo and hi Z injectors respectively. Technically speaking dropping resistors is a bandaid. Lo impedance injectors need higher current and faster reaction from the ECU for optimal operation.
In electronics it is ideal to use a lo Z source to drive a hi Z load which is why I said a lo Z ECU is perfect for driving a set of hi Z injectors. This makes the 87 ECU the most versatile. It is as strong as the 84-86 and almost as smart as the 88-89 if not just as.
Careless: (2013-07-29 03:19:13)
that's absolutely right. it definitely is the proper way of doing things even if putting resistors. the actual values are different as you said.
haven't people here reported success with just adding resistors and changing ecu's? or was that mostly for people with large injectors? could have sworn people have had success here for daily drivers?
Kingman: (2013-07-29 04:34:14)
Sounds like I was mistaken on ECU choice then. I was under the impression that if a guy added dropping resistors everything would be fine. I mean Hell, its on Jason's site as a write up.
It makes sense if the low impedance injectors require a faster reaction time and the high impedance ECUs are slower, it'd hold the injectors open longer and flood the engine. I ohmed the injector grounds anyway, 7.5ohms.
Now, I don't have Nistune. Just socketed for it with a stock tune on the EPROM - if it makes a difference.
Any thoughts on the MAF and CHTS codes and why the engine can redline without the MAF?
Careless: (2013-07-29 04:42:51)
i think by stone tone you mean stock tune just the capability of removing the stock rom and putting the nistune board in if you feel later, right?
either way, like i said - I do remember some having success with injectors resistors only… but there is definite latency difference on the maps.
thats why i don't think i'd ever bother running an ECU that requires resistors. I'd rather run one that has the capability of both high and lo z.
Kingman: (2013-07-29 04:46:50)
Correct, just a removable chip.
Yeah that makes sense. I'm retarded lol. There I go thinkin' again!
Careless: (2013-07-29 07:39:54)
are you sure you socketed the board properly? it's very tough to work on nissan boards because the pads lift VERY easily, and once you do that, you have to jump wires to surface mounted devices, which sucks balls.
any one of those pins acting weird will either make the car not run properly or act really weird.
Kingman: (2013-07-29 17:58:58)
I didn't socket it, I wouldn't trust myself and my soldering iron is way to big for that.
jaqattack02: (2013-07-29 18:21:29)
Have you verified that it's running the correct map?
Kingman: (2013-07-29 20:34:18)
I've tried two other EPROMs.
I took the truck for a drive real quick to see what it would do for shits and grins. Its got a fucking shit load of power, under half throttle. Full it sputters and pops, but half throttle feels like normal full throttle lol.
I think I'm being sent another ECU today.
Careless: (2013-07-29 21:33:00)
ok… so the car runs fine but not at full throttle? unplug your o2 and change your distributor and ptu to a pwr-2.
just try it if you have spare parts lying around. sounds like my issue with my maxima distributor i had. switched to 88 z31 and it was fine.
Augustus Maximus: (2013-07-29 21:47:25)
Shouldn't rev over a certain rpm with the maf unplugged. I would look into that if this is unchanged after you try another ECU. My shit won't even start without it.
Kingman: (2013-07-30 00:41:13)
No. It doesn't run fine at all. Its as rich as it can get, but just happens to drive okay in a very narrow throttle/RPM range. I don't have an O2 sensor and I have the correct dizzy. Remember Careless, the truck ran perfect before the ECU swap.
I couldn't believe a Nissan revved out without a MAF. Weird as shit.
Kingman: (2013-07-30 00:48:02)
Order of operation: Drove good running truck into the garage, removed '84NA ECU, broke it, installed dropping resistors, installed socketed '88NA ECU with stock '88NA tune, truck barely runs and won't idle unless I induce a huge vacuum leak.
Kingman: (2013-07-30 00:57:24)
I made a video, this is with the MAF unplugged. Plugged or unplugged there's no difference. when its idling I have my foot on the gas.
https://www.youtube.com/watch?v=BQJBZhXOZts&feature=youtube_gdata_player
Augustus Maximus: (2013-07-30 02:28:12)
Haven't seen the video(I'm at work) but if the ECU is not reading the MAF how will it know how much gas to i ject into the engine. I believe the ECU is functioning properly. Your wiring is incorrect. Faulty wiring is fooling the computer. Until the system go into limp mode when MAF is unplugged…ya shit ain't correct. Fix or buy…I have a nice 85 harness.
Kingman: (2013-07-30 02:37:54)
We shall see when I get the new ECU. Like I said I have tested the wiring many times and there's nothing wrong with it. The ECU isn't going in to limp mode, unless the '88-'89 ECUs don't have the 2,200RPM limit when in limp mode.
If there was something wrong with the harness this thread would not exist as the problem would have been fixed long ago. I wish it was the harness.
nismopu: (2013-07-30 02:40:19)
The truck ran perfect before he pulled the ecu. I heard it run the other day and went over there to listen to it. It runs just like it would with the incorrect tune like a jwt tune or something. Seems as though latency is way off......
Kingman: (2013-08-16 01:27:10)
Haven't gotten anywhere. The new '88 ECU I got won't consistently fire the injectors but will create spark. I'll be on the hunt for an '87 ECU after I get back from working in the Midwest in a month or two.
Kingman: (2013-10-29 20:28:08)
Swapped in an '87 NA wiring harness and ECU. Doesn't run. Removed the dropping resistors as well. Has injector pulse and spark.
Kingman: (2013-11-01 02:44:12)
Seems like I've got something up with my timing now. When cranking the engine locks up repeatedly but won't fire. Removing fuel gets rid of it, as does removing spark. Removing fuel and adding ether makes it lock up as well. Checked the physical timing and its spot on, retarding the distributor doesn't help at All. Still fouling plugs and raw fuel is coming from the exhaust. Tried an '85 NA ECU as well and same thing. Bizarre…
jaqattack02: (2013-11-01 13:30:35)
Injector(s) stuck open?
edicer2: (2013-11-01 13:43:29)
Idk if this well help you but if it has the pathfinder maf i had a issue where the maf ground took a shit and I had to buy that little harness from nissan that added a extra ground wire and then mine ran great again.
Kingman: (2013-11-01 14:45:40)
Right, yeah that's getting more and more common nowadays. I ohmed the new harness and its a-ok. Its all Z31 except the coil/PTU. As far as injectors go that's what Kyle and I were discussing (hydro locking) then I realized that with fuel and injector pulse but no spark, it doesn't lock up. I can see if it were trying to fire a lake of fuel though it would probably lock up…
Kingman: (2013-11-02 01:53:03)
Seems as though I have a bent connecting rod due to hydro locking from fuel causing it to lock up when cranking.
G-E: (2013-11-04 21:26:21)
How have you determined this exactly?
Kingman: (2013-11-05 05:55:57)
Kyle and I fucked with it for a long time. Shakes hard when cranking, remove fuel or spark from No. 3 and it quits locking up. Not much else makes a thud like that. Even with ether it locks up.
Kingman: (2013-11-05 06:02:10)
And when someone's eyes get huge the second you show them what something is doing and they go "uh oh, I've heard that before…" I'll see what it looks like when I pull the engine out and put a 3.3L in it. Won't be around to work on it for another few months anyway.