Correction on my last thread. The high resistance on the Temp sender was 2000 ohms and the low was 408.
Also, when I went to move her out to the drive way my power steering pumps went down making all kinds of rattling noises and got much worse when I turned the wheel.
So now I have to contend with yet a third pump in less than a year.
Anybody know a pump that lasts!!!!
Your plugs look good. A light tan is what you want with these fuel injected engines (carbs burn more earthy brown). Personally, since the van is almost 40 years old, I think it's a good idea to have an extra ECU laying around. I think you should have at least one extra of every critical part. They make great troubleshooting tools and you never know when you might have a failure. I got most of my spare parts ~ 15 years ago when you could easily find them for ~$20 on eBay, but things are drying up and becoming more expensive now. This situation will probably continue getting worse, so if you don't already have spares, grab them now.
I had a rough running issue about 7 years ago and it took a while before I got around to swapping ECU's. By golly that was it, and it was my 1st ECU failure ever. I had a hard time wrapping my mind around it so I swapped it back.........and the problem came back. I threw the bad one away because I never wanted to accidentally install it again. These early Toyota ECU's are built tough, but 35+ years of humidity and extreme temps will take their toll on anything. I'm not saying yours is bad, but it's certainly a possibility. Tim
https://www.ebay.com/sch/i.html?_fro...n+ecu&_sacat=0
Wow, and I thought I was an early bird.,
Yeah OK. Thanks for the link. I will see what part number I have and get one.
Thanks for the advice.
Will keep you posted
MT
I ordered a ECU today. Ebay had several with my identical numbers on the case.
Now I only have to pray it works.
Should have before the weekend.
MT
We just got a contribution in the form of a PDF file from member "PrecisionDriven" for those who may need help replacing their ECU. Here's a link:
https://www.toyotavantech.com/forum/...place-your-ECU
Hey this is great.
Although I have already done this, it is a great reference to have. Great Job Steve!
MT
A little up date on my engine with the shakes and idle issues.
Replaced the ECU, no change.
Something deeper here. For the idle to increase 800 RPM from just when the cold bypass air valve opens to 15 minutes of run time. My next experiment is to remove the temp senser plug from the senser and build a 20K potentiometer to put in its place. I will manual follow the temp/resistance curve in the SM to see if this can be the issues.
MT
MT - seeing as you've now ruled out all the likely suspects I feel the need to grasp at straws.
Long shot here but, is there any chance the throttle cables are mal-adjusted (throttle and/or trans kick-down)
I have seen (not on a TV) where an overly tight cable would shorten as it heated up causing a higher idle that drove everyone nuts.
I have also seen an excessively filthy throttle plate cause hot/cold idle issues
I doubt either of these things are your problem, but sometimes it's the most basic things that are so easy to overlook.
I am a little embarrassed at the number of times I have chased a ghost for hours only to find I made a stupid mistake.
Its always the little things, like the bolt you forgot to tighten cause its hidden from view, or the gasket that got folded as you weaselled a part into a tight spot, or the connector not plugged or the hose clamp that's installed on a slight angle so that its tight, but really isn't.
Burnboot:
Great idea!!!
It is very tight when cold, I made it perfect, which may be changing with heat. I will check that out.
Again, great point!!!
MT
Amen to that.......This is something every true mechanic can attest toOriginally Posted by Burntboot
Up date on this idle issue.
Replaced the computer and no change, but at least I have one just in case.
Found the temp sensor to be out of spec according to the temp/resistance curve in SM. So I replaced that. Did another curve on the new one and it was better but not perfect. It did improve idle a bit but not much.
Tried and tested the accelerator cable if maybe it was lighting up with heat, no issue there.
With a bit more studying I discovered that the temp sensor is in series with the dividing network in the Air Flow system. So it does seem that the mixture, or at least the adjustment for this system can be partly done externally by changing the resistance with the Temp sensor. The question is what does the temp sensor really do in our vans? Let's find out.
I removed the sensor connector from the sensor and replaced it with a 2000 ohm potentiometer. I picked this value since the sensor I just got was 1800 ohms at room temp, 75deg and when hot it was down to about 300 ohms.
So I installed it in the system with a stone cold engine. Adjusted it for 1800 ohms and gave it a whirl. Started right up as norm, raced at 1300 rpm during cold start air bypass valve then, like clock work, slowly lowered to about 500 and the shakes. Water temp is still pretty cool, no registration on the temp meter yet, so I decrease the pot to about 1000. No change, 500 ohms, no change, in fact no matter where I set it there was no change, no nothing. You would never know it was even there. However if you increased the resistance above 1800 RPM the check engine light came on. So it is talking to the MCU, that we know. So why is there no other change? No change in idle, shakes, exhaust gas, nothing. This leads me to the air flow controller. It is nothing but a dividing network with one leg that goes to the temp sensor and then to the MCU and another an air temp sensor inside the unit and it has a separate port for the MCU. Today I will attempt to do some DC measurements on this device and see if just maybe a resistor is open or changed in value. What I would like to do is move the flow meter's sail manually and see if has any effect on the shakes.
Then again, after driving for 15 minutes her idle claims to 1000 in drive and 1400 in park. Needless to say she does not shake here.
So the way it stands there are three idle conditions that one has to deal with.
1 30 seconds after the cold start air bypass starts, drops to 500 and shakes
2 Drive for 5 minutes increases to 600 and shakes, van jumps forward with each shake. Not pretty in heavy parking lot with pedestrians.
3 15 min of drive time no shakes, idle in drive 1000RPM and Park 1400rpm.
4 Stop for 10 minutes and no start. 5 to 10 retries to get it up and pumping pedal, must be heat soak here.
Needless to say, when she is idling at 1400 in park it is not a pretty sight putting her in gear. Ouch!!!!
MT
Update on Flow meter:
I built several different divider designs with little to no effect.
So I pulled up my pants and decide to dissect the flow meter which I did not want to do but......
Well the top came off real easy. Just a screwdriver around the parameter and wedged it up.
So there it was, this mechanism that was a mystery to me. But not any more.
It isn't really as the SM describes it. The resistors are at board level and are part of the traces themselves. Little you can do electrically. So I started her up and watched as it did its thing.
As many of you know this device also turns on the fuel pump. There is a small leaf switch that disconnects the pump from power until there is a tiny bit of suction by way of the air filter at start up. With that the door inside the meter opens and allows the switch to close. So there will always be some kind of delay for start due to this start up sequence.
Waited around for it to start to shake and manual turned the pot which of course is connected to the door. RPM goes up to a point, then falls. So I reduced my idle to compensate for the increased idle speed. Now, without any help from the throttle this baby will never run.
However, once I grabbed hold of the pot and moved it counter clockwise the idle restored to about 900 with no shakes. This is inconclusive due to the multiple issues I have but it was at least a start. I did do all the resistive tests and all were OK. I can only think that the 10% ethanol fuel I am using may be causing this. Not sure. It does seem to be adjustable but only mechanically and from the viewpoint in the van you cannot see it all. Nor would anyone would be able to do this fine detailed work. The unit has to be removed and put on a bench.
So I started looking around to see if I can find one to use as a test sample to open and determine how to correct this mixture internal to the unit.
Looked on Ebay and they are big bucks for something I would probable never use. So big educational curve here.
If anyone has or knows where to get one please chime in . It does not have to work. But this cadaver could be the answer for at least a smoother running engine. The high idle issues I am having I can deal with but getting rid of the shakes would be formost.
I found a gas station way out in the sticks that sells non ethanol fuel. It is for the landscape guys and their lawn mowers and stuff. So I am down to a little less than a quarter of the tank so I am going to drive out there this morning on the way to work and top it off with non ethanol to see if that has any effect on this.
Again, will keep all posted.
MT
MT - I hope your change to ethanol solves your issues but I am a little doubtful.
All the cars i have seen that had issues due to ethanol required parts replaced prior to running again, and every single one came in on the hook.
My ancient little outboards hate the stuff as it easts their O-rings and fuel lines and if it sits it around for any amount of time (like during the off season) it turns into a gell and clogs everything. Nasty stuff it is.
All my vehicles seem to run better on real gas but the differences are not "dramatic"
IIRC correctly, a long time ago you had some issues with tank rust and clogged injectors, have you rechecked fuel pressure and watched them while it's acting up?
Right again! It does not seem the fuel made any difference except for the price, a dollar more than reg.
I have not checked pressure since the top end overhaul. I did in fact install the super filter Tim used and I have been watching that every 500 to 1000 miles. It still catch some rust but I think it stops there. Remember I also installed another new Toyota fuel filter also that is after the super filter. So running two filters.
Checking the pressure isn't so bad but to check the injectors, as you know, is a huge job. Since the plugs burn so good I believe they are OK. Plus it runs fantastic after she is warm and over 900 rpm.
Due to the increase in RPM when I manually opened the flow door adds more variables due to the decreased idle adjustments I had to make. Now that it seems like the fuel is not going to help out, I am back to the flow meter. The SM also talks about a temp sensor in the EGR somewhere but my van does not have that.
After I got the fuel my check engine light came on. Just what I needed. So tonight I will read those codes and see what happened there.
Just too many variables.
But I will tell you one thing Burnboot, this idle problem has been with me some since I got the van before I did the engine over and the second head replacement. I thought I would also run a compression test on the cylinders just to see what that looks like. Unlikely I will see much but at least I can re-establish a base line there.
Timing is a joke due to the shakes. However, I can at least get it smooth with the air flow control and idle adjustment to try the timing light again.
Still a long way to solving this one. I am sure others have the same issue.
Will keep you posted.
We are going to find this one and share with all.
Later
MT
As you may know the Vane Air Flow Meter (AFM) uses an air temperature sensor and potentiometer controlled by a vane that moves in relation to the engine's air demand.The Electronic Control Unit (ECU) uses this information (and information from the coolant temperature sensor, and when warm the oxygen sensor) to reference the correct air density and injector duty cycle in a table in its archaic software. Some my say, oh don't forget the Throttle Position Sensor TPS, and on most fuel injected engines they would be right to say that it plays a part in fuel delivery;however, the TPS on this system just tells the ECU when the throttle is closed to allow the computer to perform a fuel cut when decelerating, and when to allow timing changes.
To make the engine start and run the ECU has (very little) control over several outputs. Think original Nintendo level of programming. All of the outputs are controlled referencing pre-programmed tables in the original software. There is no "learning" with these computers like newer ones. The ECU controls the injector pulse width (how much fuel is injected per cycle), ignition timing can be changed, the cold start injector, Air Valve (AV), and some Vacuum Switching Valves (VSV).
The AFM is the single most important input to the ECU. You can unplug all the other sensors and the engine will still run, but not if you unplug the AFM. The only way you should adjust the potentiometer, spring settings, or idle adjustment is if you have a gas analyzer, or a wideband O2 sensor installed. The AFM is amazing, I was able to install an aftermarket turbo and 100cc larger (300cc total) injectors on the stock computer all by adjusting the AFM. I did have wideband O2 as well.
By messing with the AFM you can make it run so lean it will barely run (die), burn valves, and meltdown. You can make it so rich you'll foul plugs and gas yourself out. That is why you need to know what the air fuel ratios are when you are adjusting it. If you adjust the idle using the AFM until it the RPMs are correct, you could be leaning out the entire curve. This could very well toast the engine. Even the idle screw on the AFM will change the entire air fuel curve by a couple of points.
This computer also uses open and closed loop fuel control. Open loop the computer uses no feedback from the oxygen sensor to adjust the injector pulse widths. It does this most commonly on start up, until the oxygen sensor is hot, and the engine is at least 125F, or if there is a problem with a sensor. When an engine is in open loop it is designed to provide a richer air fuel as a safety feature.
In closed loop the computer uses the input of the narrow band oxygen sensor to make adjustments to the pulse width. It does this by reporting to the computer the current rich/lean reading. These are narrow band so they do not give a detailed indication as to what the air fuel is. If the computer gets a signal of lean, it dumps more fuel, it then gets rich,and leans a bit. This happens thousands of times and minute, and the average is close to the proper 14.7 stoichiometric ratio for gasoline.
This allows for better MPG and runnability. The closed loop system on this computer has a maximum of 5% adjustment rich, and 5% lean. If fuel pressure is off it can't adjust to compensate, also if you adjust the AFM incorrectly the computer will not be able to compensate to the appropriate air fuel ratio. This can cause engine damage, poor, MPG, and poor runnability.
If it were me, I would get a wideband O2 gauge. Infact, it's the first "upgrade" all of my cars get. You can instantly know, at anytime, if your engine is running as perfect as can be. You would then be able to tell if your AFM is properly adjusted.
As far as a guess to what your problem is. Have you tried disconnecting all your vacuum lines and plugging the ports? You can do it one by one. Just to eliminate a bad VSV or something like that. Some VSVs are normally open, some normally closed, what if the wrong valve is in there? So the computer tries to idle down, but the wrong VSV is hooked up so it idles up? Just a guess.
Last edited by VanCo; 12-16-2019 at 12:22 PM.
Very nice and thorough response VanCo! You are a valuable member/asset here......Thank you!
I would also like to add the air sensing fuel pump switch in the AFM will not close during cranking (not enough air flow). The ignition switch and the "Circuit Opening Relay" bypass this feature when cranking. By the time the ignition switch returns to "Run", the fuel pump switch in the AFM takes over. Tim
Thanks Tim!
I spent a lot of time reverse engineering this EFI system to make it work with a turbo. Between a rising rate regulator, tweaking the AFM, and a pressure switch that cut the oxygen sensor only in boost to put it in open loop, I got it as perfect as could be. Now I run aftermarket injection where the sky's the limit.
Thanks VanCo and Tim:
After replacing the ECU I took a peak inside and it looks like this is using some older TTL chip sets so explains for somewhat archaic software for sure.
Well that is the first time I have had any solid feedback on the operation of this ECU. Great job and thanks.
Ironically after I went and top the tank with non ethanol fuel I got more check engine light notifications.
Reading it back was Temp sensor and O2 sensor.
I cannot really say either of these have to do with my issue since it was doing this long before these went bad. I did replace the Temp sensor last week, so I either have a bad one or the connector is bad. I replaced the connect also about a year ago.
The CO2 sensor was replaced about 18 months ago, again it only started showing up on the check engine just recently long after this idle issue.
So the first thing to do is solve these first. I will order in new ones today and will have before weeks end.
So tell me about this wide band O2 gauge. I checked a few out on the web and it looks like they come with their own O2 sender. So is this something that gets permanently installed in the van? Where does the sensor go? Do you have to drill a hole in the exhaust pipe and install this? This is something I would do right away for sure.
As for the VSV and vac hoses. This was an issue when I got the van back from the bozos that did the fuel injection work. After 10 weeks I removed the van from their lot and nursed it all the way home only to find that much of the vac hoses were wrong. I went by the hose schematic that the boys put up on TVT. I could only find 3 types of VSV, one for the AC which is very different than the rest have an extra port on it. It does make a difference if these are reversed. This has also been replaced. The other two look the same, one under the + batt on the driver side frame and one on the passenger side for the idle up (heat Soak) issue. I tried these manually to see if they work and all were OK. And then there is the one in the EGR circuit, again has been replaced. All of these hoses have replaced.
But I will go through it again as well including the hoses. So if I pull them off one at a time I should just cork the ports with my fingers and if it goes back to normal then it is OK?
The last question is how does the AFM get adjusted? When looking at it I did not see any obvious place to do that. No matter, if I put in the wide band O2 I would want to tweak the system to its best operating condition.
Great input VanCo and thank you so much for taking the time to help out.
Looking forward getting this done for sure.
MT
I would get it up to temperature and wait for it to go in to its high 1300 rpm idle. Once there, use pliers to pinch vacuum lines that would affect the idle (VSV, etc). There is an idle up diaphragm on the back of the plenum with a larger hose attached, pinch that larger hose too. If the idle drops significantly you can inspect that vacuum circuit specifically. If the hoses are fragile you can pull them and plug them instead of pinching.
The wideband uses a 6 wire O2 sensor. To install it you need to drill a hole in the exhaust and weld in a bung. Muffler shops can do this pretty inexpensively. Most kits come with the weldable bung. They also sell plugs so you can remove the O2 sensor if you wanted.
There is a large cog with a wire retainer in the AFM. Spinning that cog in either direction changes the preload on the vane. Making the vane open easier richens the mixture, making it more difficult leans the mixture. The needle for the potentiometer is slightly adjustable. There is also a aluminum capped screw. It makes changes at idle by allowing air to bypass the vane.
When the ECU gets a signal from the AFM that the vane has been at or near wide open for 3 or so seconds the ECU goes into open loop and runs rich. This is to protect the engine from running too lean at high load and burning valves etc. It doesn't take much for these van to need to run at 95% throttle just to stay out of people's way on the freeway. Since the ECU runs rich in these conditions fuel mileage can suffer. You can also use the wideband O2 sensor to make sure you stay under that threshold in closed loop.
This site has a great write up on the AFM:
https://www.4crawler.com/4x4/CheapTr...FM/index.shtml
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