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what replaced the cold start injector (1UZ) in '95?
'92-94 SC400s had a cold start injector in the upper intake manifold (plenum), but '95 did away with it. The '95 plenum has what looks like a mounting spot for it, and I've read that the plenums are interchangeable, so I'm guessing they're the same (other than '95 going to the goofy one-piece, non-serviceable IAC Valve) and '95 just did away with the cold start injector. Anyone know if the changes run deeper?
Which brings us to the obvious question: What did the cold start injector actually accomplish, if anything, and did '95+ make some change to pick up that slack? It's not clear from the limited information I've been able to find if it is purely for start-up or for the full warm-up period.
your car is very fast when the engine is warming up. As soon as you hit the normal operating temperature, it starts to slow down. This is because the cold start fuel injector has shut off.
1990-1994 engines have a cold start injector connected to a thermostatic time switch.
Those both make it sound as if the cold start injector runs throughout warm-up. Did '95 see any mpg improvement by doing away with it? It seems like my fuel gauge ('94) drops a significant amount at every start-up, which is my reason for exploring the topic ... more so than you would expect from heat expansion in the tank subsiding when shut off. I'm curious if the cold start injector leaks or if it's just spraying too much or for too long during cold driving. I've already replaced pretty much everything else that could be part of the equation.
My SC400 takes a while to start in the morning, or after it has sat for a while enough to cool completely. It takes much longer to turn over. During the day, it starts fine. I had my mechanic look at it, and if I remember correctly, he said it was the cold start injector time switch. Does this sound correct? Or would it be the cold start injector itself?
That fits more with it being a start-up thing.
I imagine the '95 ECU doesn't have controls for the cold start injector. Would putting a '95 ECU in a '94 disable it? (I'm thinking you would want to cap the fuel line to it to properly test things.) I have a '95 ECU that I could use for that test purpose. Conventional wisdom here is that you can use a newer ECU with updated programming on an older car, but not vice versa. Assuming you stay within OBDI/II generations, of course.
Here's a picture I found in an eBay listing of the cold start injector, since I didn't snap one of mine when I had it off for replacing injectors.
On the '95+ plenum, the two screw holes are there as seen in the middle of the pic, but the part that the injector slips into isn't drilled out.
One thing I'm perplexed by is it looks like only an electrical connector to the injector, not a fuel line. I'm drawing a total blank what all was hooked up when I opened things up for the injectors... Maybe it's a very thin, flexible fuel line? I'll have to get a mirror and flashlight back there to see what's what on the car currently.
I know that in 95 toyota was getting things ready for OBD2 in 96. I think the 95's are ODB2 "compliant" But still ran on OBD1
And are you sure that the 94 has the cold start injector? for some reason I remember reading some where over on Lextreme that the last year with the CS injector was 93
Thanks for the reply. I'm 99% sure '94 had the cold start injector. I recall having that line hooked up in the back when I took my plenum off a while back, and it fits what I've read.
Unless the '95 (or '94, if you're right) ECU modified injector signals to account for no cold start injector, the only conclusion I can come up with is that it was superfluous all along. It's not like power was down when it was eliminated.
FWIW I have a 95 sc400 (ecu 89661-24410), and because that ECU needs a refurbish I've been somewhat successfully using an ECU from my 92 sc400 (ecu 89661-24240) parts car. There are some noticeable differences driving the car:
1) During a cold start the absence of the cold start injector on the 95 1uz makes cranking time quite long but the engine eventually does fire. My temporary remedy for the long cranking time is to bump the starter for about 1 second, then crank once more and the engine fires as it should. This is only required usually in the morning when coolant temp is cold. Any other start attempt during the day happens properly as it should.
2) The 95 sc400 does not have a mechanical transmission kick down switch that the 92 does. So depending on the speed I'm travelling the the transmission won't kick down a gear or 2 at WOT like it did with the correct ECU. My remedy for this was to manually shift the lever into the lower gear as long as I was travelling at the correct speed for that lower gear (it says the speeds for each gear in your owners manual). The torque converter lockup worked as it should as well. However I swapped to a W58 a couple weeks ago so no more auto trans for me!!
These were the only things that stuck out for me and I'm pretty observant about what's not working like it should. Even my manual swap works, runs, and drives pretty much as close to OEM as possible including operational cruise control, memory seats and traction control. Which is commonly left inoperative.
Just putting this info out there from my first hand experience. Hope it helps. A sorry for the long post, tried to word it as clear as possible.
Lots of interesting info here. '94 is an oddball year with transitional part numbering, but apparently so is '95 with some stuff such as gauge clusters. That may prove relevant...
Originally Posted by CorMan
FWIW I have a 95 sc400 (ecu 89661-24410)
Same part # as my spare '95 ECU.
1) During a cold start the absence of the cold start injector on the 95 1uz makes cranking time quite long but the engine eventually does fire. My temporary remedy for the long cranking time is to bump the starter for about 1 second, then crank once more and the engine fires as it should. This is only required usually in the morning when coolant temp is cold. Any other start attempt during the day happens properly as it should.
Whoa. That's the major issue I've chased on my '94 since buying it. I've got it 80-90% improved, but never totally eliminated. I still get the long crank on the first drive of the day, so it may well be what you're saying with the coolant being cold. I also did the quick bump method for a while to get it to start immediately on the second try. My symptoms sound like a '92-94 ECU on a '95 car...
Edit: Upon further thought, I was probably right to suspect the cold start injector having some role in the long cranks, but for the wrong reason. I figured it was leaky, but it might be that it simply isn't working, creating the same effect as a '92-94 ECU on a '95 with no cold start injector and no modification of the injector signals by the later ECU.
So, if the '95 takes longer to crank cold with an earlier ECU, it stands to reason that the '95 ECU is modifying the signal to the injectors, right? Now I really need to pop in my '95 ECU to test.
2) The 95 sc400 does not have a mechanical transmission kick down switch that the 92 does. So depending on the speed I'm travelling the the transmission won't kick down a gear or 2 at WOT like it did with the correct ECU
So, the kick-down is electronically controlled (by the engine/tranny computer) on '95, instead of mechanically? The transmissions are the same, so what changes in how they're hooked up? I'm not familiar with that aspect. Would a '95 ECU confuse it by having two control inputs?
My assumption is that in the 95 ECU the injection parameters are different for cold start. As for the transmissions they're hooked up the same however my guess is 92-94 chassis required input from TPS, kick-down switch, road speed sensor and fluid pressure cable attached to the throttle body to properly govern up shifts and kick-down. Whereas the 95 chassis eliminated the mechanical kick-down switch and uses more so TPS signal, road speed sensor and fluid pressure cable to do the same job. Again just my assumption.
I swapped in the '95 ECU for a test, and on cold starts yesterday and today, it definitely seemed like a shorter crank. (A lukewarm-ish start 5 hrs later was closer to normal, however.) I'll have to test it a few more days to be sure it's not my imagination.
The transmission control also feels ever so slightly different, like it downshifts quicker on its own without needing extra throttle input. Again, I need to test that more.
If the shorter cold start cranking does prove to be repeatable, I guess I'll have the choice of using the '95 ECU and stripping out cold start stuff, or going back to the '94 ECU and trying to troubleshoot the cold start stuff. I'm right in the middle of porting and shaving the spare intake manifold, including total removal of the EGR tube and related pieces. I left the un-drilled cold start injector mount on in case this thread bears out the need to retain that feature.
The two negatives to the '95 ECU are the O/D Off light flashes (probably related to CorMan's explanation of the tranny control differences between '94 and '95), and a CEL which unsurprisingly is #71 for EGR. '95 went to a more advanced sensor and connector, so even if my '94 EGR weren't deleted, the '95 ECU would probably still throw that CEL. Aside from those two annoyances, this at least confirms that a '95 ECU can work on earlier years.
The one surprising thing was the weight difference. It's not something I had thought to measure, but as soon as I pulled the '94 ECU out and picked up the '95, I knew there was a significant difference. It turned out to be exactly 3 oz, which may not sound like much, but it's nearly an 8% difference, with the newer one being lighter. I'm guessing they went to some lighter materials, because everything looks very similar if not identical.
its simple, the older 1uz ecu was a batch fire ecu (injectors are fired in pairs of 2) with a extra cold start injector pulsed by the ignition switch being activated. this is because the 1uz was actually developed in the 80's and was carrying over that technology they used in japan on the same 1uz motor.
in 95 or 96 they went to full sequential fire ecu's (each injector has its own driver) to get ready for changes in obd2 and to meet higher emission standards, cause batch fire emits more emissions at idles etc... and majority of toyota motors by 95 had this technology anyways (the 2jzge was always full sequential fire and has no cold start injector). They got rid of the cold start injector and the ecu was programmed to pulse the injectors to help with starting the car, basically with the better ecu the cold start injector was redundant and deleted, but the engine didn't change so they used the same intake without drilling out the cold start injector.
you are not supposed interchange these different year range ecu's, not only is there the difference in cold start injector but the difference in injection, the batch fire engine harness only has 4 wires running from ecu to injectors (paired off remember), and the full sequential ecu/harness has 8 wires running from ecu to injector. so if you use an older ecu on a newer harness you would be running on 4 cylinders, but if you use a newer ecu on a older harness then I am not really sure what happens it might work out ok depending on the pin locations since half of the 8 signals will get sent to the 4 wires which go to the 8 injectors, so it might run alright but still not ideal those drivers on the newer ecu are designed to run 1 injector each, not 2 like the previous generation so there may be burning out issues in the future.
to change ecu's to a different year range properly on a 1uz, you would have to change the harness also, or modify the harness, and delete or add the cold start injector as necessary to match the ecu.
also the older ecu's like 92 use a switch on the bottom of the gas pedal for kickdown, so it knows you have pushed it all the way to the floor...
somewhere in the year range they got rid of that switch and the ecu just looks at the tps to know when you are doing that.
you can install the switch like the 92's had, or just get the right ecu. honestly refurbishing your original ecu s always best if it can be salvaged.
if you are using the 95 ecu on the 92, I would unplug the cold start injector, chances are the new 95 ecu is pulsing the main injectors for cold start, and then the cold start injector is also being mechanically activated cause its mechanical on the older 1uz's and has nothing to do with the ecu (its a timer circuit based on the ignition switch, like old school toyota's have), so you are actually getting double the cold start fuel.
thats why it takes so long to crank before it starts its actually spitting out excess fuel until it has the right amount to start.
if you had too little cold start fuel, it wouldn't start no matter how long you keep cranking it. so I think you guys using 95 ecu on a 92 have too much fuel for cold start, not too little.
unplug the cold start injector and try it I bet it starts a whole lot easier.
In that picture above, its missing the fuel line that goes to the injector. see the bolt that goes through the injector?? see how tall it is?
its taller cause the fuel line is hard metal line with a "banjo fitting" on the end (look like a bolt hole) that gets bolted down on top of the injector, and the fuel passes through the bolt and into the injector then into the intake. the line can be bent a little but it weakens over time since its metal.
in 95 or 96 they went to full sequential fire ecu's (each injector has its own driver) to get ready for changes in obd2 and to meet higher emission standards...
to change ecu's to a different year range properly on a 1uz, you would have to change the harness also, or modify the harness, and delete or add the cold start injector as necessary to match the ecu.
Originally Posted by pogoism9
The SC4 moved to SFI for the 1996 model year. The LS was 95.
Thanks for that clarification, pogoism9. It's been a busy day today. I got Ali's email notification earlier but didn't have time to check in until now. I was puzzled how to resolve my trust of his knowledge on the matter with it not making sense, because, well, the '95 ECU obviously does work on the '94. That LS/SC one year difference in generations has certainly confused its share of topics.
also the older ecu's like 92 use a switch on the bottom of the gas pedal for kickdown, so it knows you have pushed it all the way to the floor...
From CorMan's explanation a few posts up, it sounds like the '95 ECU would control that kickdown regardless of the old switch.
you can install the switch like the 92's had, or just get the right ecu. honestly refurbishing your original ecu s always best if it can be salvaged.
My '94 ECU works just fine and has been serviced. This is purely a research experiment. When I started looking into it, I was able to find very little information about the cold start injector.
if you are using the 95 ecu on the 92, I would unplug the cold start injector, chances are the new 95 ecu is pulsing the main injectors for cold start, and then the cold start injector is also being mechanically activated cause its mechanical on the older 1uz's and has nothing to do with the ecu (its a timer circuit based on the ignition switch, like old school toyota's have), so you are actually getting double the cold start fuel.
thats why it takes so long to crank before it starts its actually spitting out excess fuel until it has the right amount to start.
if you had too little cold start fuel, it wouldn't start no matter how long you keep cranking it. so I think you guys using 95 ecu on a 92 have too much fuel for cold start, not too little.
unplug the cold start injector and try it I bet it starts a whole lot easier.
Very interesting, thanks for explaining that.
In that picture above, its missing the fuel line that goes to the injector. see the bolt that goes through the injector?? see how tall it is?
Yes indeed, I see it now. So, to test your above theory, I would leave the banjo bolt / fuel line connected but unplug the electrical to disable it?
yeah the whole 95 or 96 thing is tricky to say the least. the newer ecu shoud control kickdown off the tps yes.
yes, just disconnect the electrical connector to test it.
That does seem to have worked well, disconnecting the electrical for the cold start injector along with the '95 ECU. I'm pretty sure it started up quicker (i.e., immediate), certainly not any worse. How loopy that I started out thinking that the cold start injector (CSI!) might be leaky and causing fuel pressure loss, then figured the faster starts with the '95 ECU indicate the CSI was under-fueling, only to learn that it was more likely the CSI was over-fueling.
yeah sometimes its not the simple things. if it leaks, it would leak with or without the connector on it, and would keep leaking which would probably affect how it runs after the start. if there was an improvement from disconnecting it then I was probably right.
it still amazes me that the sequential injection ecu can run the motor with the batch fire harness, but you guys are likely right and they didn't do that till 96 then on the SC, cause a 92 ecu shouldn't work on a 96 car, but a 96 ecu may work somewhat on a 92 car because of how the harness is wired (but I still think it wouldn't be "right"). so since one of you has a 92 ecu on a 95, I would think the 95 still uses the older batch injection as well, or it would be running on 4 cylinders.
it is also odd that in 95 they ditched the cold start injector, but the injection system wasnt upgraded till 96. I would just keep trying combinations till it all works again.
I imagine if someone were to try the same thing with a '96 ECU, they would run into the sequential vs. batch fire problem.
Originally Posted by Ali SC3
it is also odd that in 95 they ditched the cold start injector, but the injection system wasnt upgraded till 96.
That is a head scratcher, huh? It's what got me thinking at the start of this thread that some change in thinking rendered the cold start injector useless. The sequential firing change didn't occur to me, though.
FI-25 of the factory service manual covers the CSI, although it takes 6-7 pages of disassembly instructions before getting to the diagnosis steps... It looks like the CSI isn't the sort of thing that can be sent off for cleaning and flow testing like a regular injector, rather you just test resistance, spray pattern, and drip rate for leakage. The steps are heavily dependent on special service tools, but hopefully there are workarounds for that. Also, FI-87 has inspection steps of the CSI time switch.
09-26-15, 10:57 AM
what replaced the cold start injector (1UZ) in '95?
