Mtnmann

Update: I got a compression tester, checked the problem cylinder and got only 80PSI. The cylinder next to it gets 140PSI. It seems likely that something did fall in there. I was being careful but it seems not careful enough. I should have covered the holes and always will moving forward. Expensive lesson learned by a shade tree mechanic I suppose... It also seems possible that one of the injectors was stuck open but may not have anything to do with the mechanical problem I'm having now.

The injectors are on their way back to the seller for a refund and the motor is coming out this weekend. I will pull the head off and reveal the final verdict. Then I will spend all my time in the 3.4 swap section. Again, thanks to all who helped out here.

Robert m

iTrader: (2)

When I was looking at the ebay listings for these i asked about the injectors and what were what. the seller told me that the cheaper gray ones would work better for me, that they were the better injectors, and should not cause any rich condition.

Either way, I like the ones I got and after a little tweaking with the AFM, it seems to be running great with better MPGs and it passed smog.

RSR

Yes, I got the same answer from him, but I think he's wrong...

It's all about closed vs open loop on this early OBDI ECM. In closed loop, the ECM is using input from all sensors -- the 02 sensor being the big one -- to adjust the air/fuel mixture. In open loop (startup until engine at temp, at idle, and wide open throttle -- think actually >80% open), the ECM just references tables/spreadsheets that tell it how much fuel to inject ignoring sensor input with the assumption of everything operating as setup from the factory -- the engineers knew the approximate air flow (at idle, with the AFM air bypass screw setting -- blocked form adjustment with the plug) and at wide open throttle knowing the air intake rate/limits of the engine setup...

So if adding more fuel and/or adding more air, the AFM bypass screw will need adjusted for idle, and AFM spring tensioner will need adjusted for wide open throttle. With those two tuned to similar #s as to what the stock setup is, the ECM should be able to adjust air/fuel ratio to programmed ideal #s.

That's why the wideband is so important. Assuming you're truck is working properly and sensors are in spec, getting pre-mod #s will allow you to tune once you change air/fuel flow. Running too rich, and you're wasting fuel that won't fully burn -- and potentially burning up your cat's core. Running too lean and you risk burning a piston. The benefits of modding in this instance should only be done the right way as the risks and/or costs of doing it halfway far outweight the rewards of doing it right... The AEM Kit looks to be the best bang for the buck: http://www.ebay.com/itm/331045755018

For an easy, simple swap, go w/ the orange as they have the same flow. If you have the supra AFM and are doing other flow mods on intake and plenum and oversized valves -- and fully building out your exhaust, you probably want the grays. But short of that or forced induction (turbo/supercharger), and with this engine running rich in the first place, I think the orange should suffice.

Gamefreakgc

Almost. The O2 sensor does more than you would think. It adjust for too much air and too much fuel. So even though the grey ones up the fuel output slightly (8% is hardly anything) and the ECU doesn't know it, the O2 sensor will adjust the fuel trims down. My rig is a great example of that, I set everything to stock injector specs and it keeps giving me long term rich signals (vf1) even though the ECU doesn't know flow was increased by 8%. It's the O2 sensor that is giving the correct reading.

RSR

Partially right -- in open loop, the 02 sensor input is not considered. It's internal, preset maps/spreadsheets/ratios that do not take any sensors into consideration. This is the main things folks are talking about in regards to performance flashing the ECM (a real pain to do on any Toyota -- they try to keep shadetrees out of them...).

In closed loop, the ECM is controlling while reading all the various sensors... The one that matters most is the 02 sensor as you mentioned.

Good explanation: http://www.enginebasics.com/EFI%20Tu...Loop%20o2.html

And if you head over to supra forums, there's a lot more info on tuning the OBDI Toyotas; sure there's some better ones, just a uqick search:
http://www.toyota-supra.info/forums/...rstanding.html
http://www.toyota-supra.info/forums/...ice-print.html
http://www.mkiiisupra.net/bbs/archiv...hp/t-2326.html

Gevo

So, what was the cause of the engine issue?

stanprophet

Oh it can happen very fast if the injector was stuck wide open.

HighLux

It would hydraulic a rod before washing rings if in fact said injector stuck open.
You are thinking cast rings on carbed cars from days gone by.

stanprophet

Not saying you are wrong, because that is usually the case, but there are also exception. I have had 3 vehicles towed in in the last 6 months with injectors stuck open, low compression on that cylinder, and raw fuel and white smoke pouring out of the exhaust.(Raw fuel passing through a super heated catalyst make some very dense pure white smoke as it is evaporated)

2 of the vehicles were fixed with an injector change, spark plug or plugs, and a little bit of oil in the cylinder and a long test drive. One was an injector coil shorted, and took out the injector driver on the PCM due to the decreased resistance in the injector, the current flowing through the transistor was more than it could handle. We also commonly get vehicles towed in that sound like a compression issue, but have washed down cylinders due coil failures taking out the coil fuses.

I will get back on subject here.

OP I would squirt some oil in the cylinder, and disable the fuel pump. Do a compression test again on the cylinder and see if the compression comes up. If it does that is a good indicator the compression issue may be washed down rings. Unfortunately the knocking sound is not a good sign, and makes me think that the cylinder may likely have another problem. Before you tear the engine down, it may be prudent to put a vacuum gauge on the intake and see if the needle fluctuates rapidly, this will give you an indicator if the problem is in the valve train.

Normally when a foreign object enters the engine via the intake runner, either upon entry past the valve, or after coming up on the piston on the intake or exhaust stroke it will strike one of the valves. This obviously plays hell on the valves, valve seat, combustion chamber, and piston top. The dynamics of this situation, it is hard to say if the cylinder was hydro locked with fuel because of a stuck injector. Or if a foreign object entered the cylinder, and the raw fuel was from the injector also being stuck open. I have never seen a dead hole cause fuel to pour out of the exhaust due to a misfire. Every time I have seen this it has been an injector, PCM driver holding the injector open, or a ruptured fuel pressure regulator diaphragm.

If you could post some pictures of the spark plug that was damaged it may give an indicator of what may have caused it. Liquid in the cylinder can bend and break spark plug electrodes. Usually it is flattened with no dents or marks on it. We see this a lot in my area, when we have huge storms, and people think they can make it through deep water if they floor it through the 4 foot deep river crossing the road.

Hydrodynamics, and Pascal's law become quickly apparent to them.

stanprophet

Keep in mind on open loop, Priority sensors are looked at to determine the correct air/fuel map to consult. To some degree the pecking order of priority sensors are ECT, MAF/IAT or MAP if its speed density, TPS, and of course the RPM signal. The ECT is the #1 priority sensor, it determines if the operating temp dictates open or closed loop. It also sets the baseline map.

Mtnmann

Wow, it took a long time to get back with the culprit but the motor sat for quite a while after doing the 3.4 swap. I finally cracked it open and it turns out that a washer fell off of the intake manifold and into the cylinder. I had a long extension holding it all up while I swapped the injectors and I bumped it loose at one point resulting in the intake falling down. A washer must have stuck to the manifold and knocked loose and falling down the hole... The piston, head and valves were beat to hell so the motor was scrapped except for the good head and accessories. I hate it when these things have no ending so there it is!