Beater-truck4life

Hey guys, I've been working on and driving a 1993 t-100 (3vze) and I've come across an issue that is just puzzling me. The truck was sitting for 6 years but only had 93k on the odo and a mint frame so I picked it up for $300. New fuel lines, fuel pump, head gaskets, timing belt, plugs, wires, cap and rotor... After I finished all my work the truck ran great for 3 months then I acquired a code 53... Knock sensor issue... New pig tail, new sensor and it was running great for 2 weeks and all of a sudden crapped out... I set the ign timing at 10 deg after installing new knock sensor and in 2 weeks the truck just slopped out. Current diagnosis is a misfire on cylinders 1-3-4, plugs seem wet but spark when pulled and plugged in... I'm looking for advice bc if not I'll prob pull the intake man and put another knock sensor in and see if the new one I purchased was just faulty. Any information would be greatly appreciated.

Beater-truck4life

Misfires all happened at the same time one day.

Beater-truck4life

Just an update, compression in all cylinders is greater than 160, tried swapping in a good maf/gate on the intake, working ign control module and coil, working distributor, new cap, new rotor, new plugs in misfiring cylinders (ngk gapped to .040), pulled timing cover and inspected timing belt... Checked ignition timing (set to tdc pulled distributor, rotated crank 360 and reinstalled distributor but the truck wouldn't run so set it back and set ign timing to 10*)... I'm about stumped unless the it's an injector issue... Is there a common ground or wire to fail? Cylinders 1-3-4 are still dead when I pull their plug wires.... Any advise or direction? Going to pull the intake manifold and ohm injectors next

DallasTX

Wished I could help more, but seems like you are on the right track. Since 3 went dead at the same time, I think your thoughts on a common ground is a good place to start. Seems unlikely three injectors would fail at the same time. Also strange that they are not all on the same side. When you ohm the injectors, consider checking continuity to ground on the injector wiring. One of the two terminals has to go to ground. My 92 wiring diagram indicates the ground is black with red stripe and positive is white and white with a red stripe. If it helps, I will post picture of the wiring diagram....but it is for 92.

Beater-truck4life

On a second thought, I have an ecu in my spare parts truck and I know of another one in a t100 at the junk yard. Going to pull those tomorrow as well as injectors out of my parts truck... With the misfire being on opposite cylinder banks I'm leaning hard towards the ecu. I did have a buddy spray some starter fluid in intake hose that would normally go on the valve covers while I revved it up and the motor took off on all cylinders. Def an injector problem. Crossed fingers on ecu swap tomorrow

DallasTX

My ECU experience is very limited so cannot comment how its failure affects components, but sure seems like a likely source since it appears you are not getting power to the three injectors. Hope the swap gets you back on the road.

Since three injectors failed at the same time, it is probably not the injectors themselves. One caution about swapping the injectors pulled from your spare is you are introducing new unknowns to your problem. If you think it might be the injectors, ohm the current ones or pull and test them. Resistance should be 13.4-14.2. You can also test with a 9-volt battery to see if they actuate. They make a very audible click. I made up a spare connector to connect a test lead to the injector and just quickly touched the wire to a 9-volt battery three times just to see if it would actuate. Since you have a donor truck you might have access to a connector.

Co_94_PU

iTrader: (-1)

Injectors clogged?

its not likely an ECU problem since the injectors are batch fired

DallasTX

Please elaborate on how the injectors are batch fired. Are they all fired at the same time, two at at time, etc? Just curious. Always trying to learn.

Thanks

Co_94_PU

iTrader: (-1)

The pinout on the TCCS ECU shows #10, #20 as the injector signal lines. This gives two banks. However once you dig into the EWD (electrical wiring diagram) or start probing the lines with a multimeter...



The octagon shape indicates a splice point, then gives it's designation. This changes the two banks into a single batch. They will all open at the same time (batch mode) regardless of which injector driver (Bank) circuit is activated.

It's not really known what happened during the engineering, but we can probably blame accounting. Typical manufacturing design flow goes like... Engineer A designs the system, engineering group B ok's the design, then it gets kicked to C who's job is to cut costs.

So engineer C desided the power circut in the ECU could use a cheaper part (transistors, or injectors) or less parts than was originally designed.

For example the injector drivers. Each driver has a high-power transistor and associated passive components (resistors, capacitors, coils ECT). Say that costs 1$ for each driver circuit. If engineer A designed and spec's six drivers for the 3vz to have sequential injection were at 6$ per ECU multiplying for say 50000 ECU's that's $300k. Going to a batch firing with just two drivers brings that down to $100k.

Now we've reduced the part count, the next step is to reduce the safety margins of the components to the minimum. In this case they went with a different transistor, say they went from a .75c transistor to .50c they saved another $0.50 per unit were down to $75k for a 50k unit run. This will have a lower power rating and heat dissipation characteristic. Which means it can not "turn on" hard enough or fast enough without overheating. This was solved by connecting the two banks at the splice, then alternating between the two driver circuits allowing them "off time" to cool between injector pulses..

Now of course my $ figures are just random easy to follow numbers and don't account for circuit board space, wire or anything else. The actual cost per channel for a sequencial mode is probably more along the lines of $10 or more. So the cost reduction phase probably saved them millions, and that's just across one ECU type and vehicle.


I have not gone through the effort to verify the consensus that the banks are interconnected, but people more vested in the outcome indicate that they are spliced into a single batch.

Still following?

Take the four cylinder for example. Being a four stroke type engine, with intake, compression, power, and exhaust strokes. At any given time we have all four things happening.
#1 power
#3 compress
#2 exhaust
#4 intake

​​​​​​So the ECU will open the injectors with 25% of the calculated fuel in batch mode, or 50% in banked firing, at each intake stroke.

​​​​​​​It's similar on the six cylinder but I don't want to wrap my mind around those extra two cylinders to break it down to cam angles.

DallasTX

WOW! Thanks for the detailed explanation. I just assumed each injector would provide fuel to its cylinder on its intake stroke, but if I read your explanation correctly, all six injectors actuate simultaneously on a 3VZ, but just inject a fraction of the total needed fuel each time they open.

I saw what looked like two splices in my wiring harness where it runs across the front of the engine, and I am the only owner, so I know it was factory. Did not trace the wires, but thought it was odd.

Thanks again Co 94 PU for such a detailed explanation. Sorry Beater for hijacking your thread, but definitely good info.

Beater-truck4life

Well just to close out the thread, ecu swap changed nothing. However while I was at my parts truck I broke down the upper intake mani and robbed the injectors. Pulled my intake and inspected the injectors... The 3 dead cylinders (1-3-4) had injectors that were totally clogged. 100% relieved to see this believe it or not. Flow tested the injectors I pulled from the parts truck (thanks for the 9v battery hack) and tossed them in. TRUCK IS FINALLY RUNNING AGAIN! Adjusted ign timing again and set at dist at 12*, fueled the truck up and took her out to do hood rat beater truck stuff. I know my daughters and wife were going though beater truck withdrawals! Thanks for the help guys.

Beater-truck4life

scope103

Uh, not quite.

The B-R line to the injector is always 12v with key-on. The injector is opened when the ECU GROUNDS the W or W-R line. So with the engine not running you will have 12v on one terminal and disconnected on the other.

The injectors are grouped into two banks; 1-3-5 on the W-R line, 2-4-6 on the W line. But even though there are two banks (separately connected to the ECU), it is true that they all open at the same time. http://www.cygnusx1.net/Media/Supra/...taTech/h22.pdf