whokrz

A lean mixture causing a miss fire could be a hole or numerous small cracks in the hose that connect the throttle body and the air flow meter. This would allow air to bypass the air flow meter causing it to run lean. The hose at the throttle body gets hard and cracks form on the bottom side when the air filter is changed with out loosing the clamp on the throttle body. Normally this causes a low idle though which you have not mentioned or you just have the idle screw turned way up. If it has cracks and you are unsure if they leak you can wrap the hose at the throttle body in duct tape to diagnose it.
Just thought I would bring it up in case the shop comes up empty.

ycmike

That's a good thought and others had mentioned this as a potential problem area.

I did remove and inspect the plasic ducting and the rubber ends. The end at the TB did have some cracks on the bottom however they looked superficial. To be sure this was not the problem, I wrapped this rubber end piece with electrical tape. Unfortunately it did not make any difference in the way the engine was running after warm-up.

pkelly

ycmike-

I have the same problem with my '90 22re pickup. This thing is KILLING me. I have checked, tested, and replaced everything I can think of.

I've been scouring the internet looking for possible solutions I might have missed. PLEASE, if you find a solution keep us posted.

Thanks. And GOOD LUCK!

-Pat

ycmike

Pat,
I feel your pain. I'll be posting what the eventual outcome is with this engine whether fixed or not.

You might want to start a new thread here with the specifics of your truck and the problems you are having. This would provide more data to others who might be having the same or similar issues. I would be interested as well to know more specifics about your situation. As a benefit to you, its a way to document what you have done and it just might help you or others realize something that was missed.

This seems to be somewhat of a plauging problem with some of these engines/trucks. It's interesting that mine had run great for years and this problem did not start until the engine was rebuilt. This make me hopeful that it can be fixed.

pkelly

thanks for the encouraging words Mike.

I will try to start a new thread detailing the lengthy history with my truck as soon as I can find a spare couple of hours... hahaha.

I also should mention I have a call in to the local community college that has a toyota training program. I have no idea when I'll hear back, but it's a shot for me. The teachers over there are extremely knowledgeable.

Good luck and thanks again.

Pat

Jaysun

I am having the exact same problem with my 1986 4runner. I noticed that the vacuum to the EGR is starting at around 2200 RPM when the book says it should not get a vacuum until 3500 RPM, However nothing says what would cause this problem. So I am at a loss also. (without the EGR connected everything works fine!) However I need to pass smog..

thook

Jaysun.........sounds like you're having an issue with the vacuum modulator.

Read this:http://www.autoshop101.com/forms/h61.pdf

Why don't you start a thread, though, where your issue can be discussed if you have anymore questions? You'll get more responses that way. As well, Mike can keep his thread on topic.

ycmike

Jaysun,
Can you point me to the book/reference for the 3500RPM?

I don't recall reading that the EGR should only get vacuum at 3500RPM and above so maybe I missed this in my troubleshooting...I would like to have a look at the reference.

My engine was definitely getting EGR vacuum signal starting somewhere around 2500RPM. At 2500RPM the vacuum was low, several inches, but it was not 0.

By the way, the shop that has my truck believes at this point that the problem on mine is indeed the EGR. As far as I know they have not resolved the problem but they are thinking that the engine is getting too much EGR gas into the intake. Their plan, as I understand it, was to put the truck on a roller (calif smog II machine) with smog/tailpipe sniffer and monitor emissions while *adjusting* the amount of EGR gasses going in to the intake by either using a vaccum delay valve or perhaps a fabricated EGR restriction plate. The hope was to find a lesser amount of EGR gasses which would still keep the engine from producing NOX but not causes the misfire.

I'll let you know what they find.

Jaysun

Mike, Attached is a picture from the Toyota repair manual that shows the EGR test should only get a low vacuum at 3500 rpm. today I replaced the vacuum modulater with no noticable change. I am also considering replacing the gasket between the plenum and the EGR with another one that has a much smaller hole to limit the maximum gas flow. I am very interested in the results from you mechanic.
Cheers
Jaysun

ycmike

Jaysun,
Thanks. I believe step 5 is what you are referring to. Interesting, I did not interpret that to mean it should *not* get vacuum below 3500RPM. I interpreted it to mean that it should have *low* vacuum at 3500 and not something else like no vacuum, high vacuum, or near intake vacuum. On mine, it did have low vacuum at 3500 when gauge was "T"ed into that line. As I mentioned before, the vacuum started somewhere around 2500RPM and stayed *low* up to 3500.

When I was doing that test I was thinking to myself that the manual could have been written much better. Like explaining what is good and what is bad. I think the manual leaves it open for some interpretation.

In a no load or light load state the vacuum should stay low because there should be little back pressure. If back pressure increases, the modulator valve will close an internal vacuum path which will then allow full signal vacuum to be applied to the EGR valve.

Jaysun

Mike, You may be right regarding the meaning of the RPM vacuum test, It should be more clear in the manual. I think what we need is another good running engine to compare with.
I tried making a new gasket with a much smaller hole to replace the one between the plenum and the EGR, There was no change at all with the hole reduced to the size of a pencil, However I reduced the hole even more and things started improving.
I am not happy with this solution since it required such drastic restriction that I dont think the EGR is able to work very well.

I appologies for not starting a new thread, I have read everything from the start of this thread and can only say "ditto".

Jaysun

YCMIKE,
I have been looking into the possibility of a partialy clogged cat converter causing an excess of pressure upstream thus forcing more exhaust back through the EGR and causing the intake to be too lean. I am going to look into this on my rig tomorrow but thought I might mention it to you and see if you think it could be usefull to you also.
Cheers
Jaysun

Jaysun

Sorry,
After re-reading this thread I noticed that you already checked the Cat for clogging.

myyota

Its possible that the misfire your getting is being caused by a lean condition, if so, then replace the 02 sensor. The computer uses the 02 sensor to set the air fuel ratio and if its bad it can cause the problems your having. I replaced the 02 sensor in my 86 4Runner because it was the original one with over 300.000 miles on it. so if your 02 sensor is original it would be a good idea to just replace it.

thook

myyota.......hmmm.....a bad O2 can cause problems, but if he has lean condition it doesn't mean the O2 is bad and needs to be replaced. On the other hand, if the correction value is more than the ECU can compensate for, disconnecting the O2 can help pinpoint the issue. If it runs better without the O2, then that's probably it. But, there's other sensor factors involved in A/F ratio. O2's really only affect operation in closed loop since closed loop is all about utilizing the O2 feedback for fuel trim. If the problem occurs in open loop as well, then it's something else. In open loop, O2 input is ignored even if the O2 is detecing a rich or lean condition.

myyota

That is true, but he said the problem was happening when the engine was warm
(i think thats what i read), and when the engine warms up it goes into closed loop, so the 02 sensor is being used at this point to set the air fuel ratio, isn`t that how it works ?.

85gijunk4x4

my 22re is doing something very simalar

ycmike

I did replace the O2 sendor with a Denso brand and the problem did not change.

ycmike

The problem is fixed. The post I made earlier about the EGR orafice size was the fix. It was reduced to a 1/8" opening and the misfire is almost completely gone. The engine still passes smog with this size opening.

I suspect that the reason the problem started after the rebuild was that I throughly cleaned everything before putting the engine back together. This included the TB, all TB vacuum ports, the air plenum including the EGR passeges. I suspect that either the TB vacuum ports were restricting vacuum to the modulator or the EGR passeges were restricting the EGR gasses to the intake.

The EGR which I had installed was a toyota OEM part and it had an opening of about 3/8". The shop said that this was very large for such a small engine. I can't explain why this would be this way.

Next step is to drive it and see how the engine runs after several hundred miles. The engine was rebuilt using Rock products including the rings. I've been following the other thread on Rock rings not sealing so I'm keeping my fingers crossed that the rings seat ok in this engine.

Jaysun

YCMIKE,
I tried the same solution also with the same result, However I am still convinced this is only compensating for something else that has stopped working correctly. With that said, I will also state that I am about to give up trying to find anything else, Ive spent too much time and money on this stupid problem. It just doesnt make sense, It used to work fine without a custom made gasket to restrict the EGR.

Anyway, If I do find anything else I will post it here.

Cheers

Jaysun