I've replaced:
plugs
wires
cap and rotor
fuel filter
oil filter
oil
oxygen sensor
checked air filter

Problem:
I'm losing horrendous amounts of power. I'm very well aware of the 3.slo's reputation. However, up until a few weeks ago it's been running great. I've got a 5spd, 4.88's, and 32x11.50 AT's. I used to have tons of power, I could practically race other pickups. Problems started out as a hesitation at idle and where i normally shift into 4th it would be a little rough. It's kinda grown though. On the highway I have no power at all, and going up the hills I used to race up and have no problems, I'm now struggling to go up at all. After what I've already replaced I figured it was a timing issue. So I bought an inductive timing light and tested it it. I'm getting right at 10 btdc(jumpered), but a little bit of flickering. Every once in a while it will drop down for a split second to around 8. I adjusted the timing down to 8 btdc and it's about the same. I noticed with the light it seemed to be a steady strobe, but everyonce in a while it would miss a blink. So I looked in my chiltons to figure out how to test my coil, and it appears my coil is different than what is in the picture. I've got a coil and igniter that are vertical. Both next to each other. Not the cylindrical style coil. I thought you check the resistance with the engine off, but I don't get any reading when jumping the pins. Not from the 2 pin plug or the 4 pin plug. But the engine does run. So I don't know if I'm just testing it wrong. What would you guys suggest here? Does it sound like a coil problem?

 

Oh I'll add. I remember reading something about putting a piece of paper over your exhaust to check the valve timing. It is being blown away from the exhuast with an occasional suck in towards the pipe. Don't know quite what that means. But hopefully someone does.

** oh yeah, no codes at all **

 

First of all, forget Chiltons. It's junk... They cover too much in too little detail in too small of a book, and do it very poorly. Unless you are a mechanic (and then you wont need Chiltons) these one-book-fits-all manuals give you just enough knowledge to be dangerous. If you plan to keep the truck, get factory service manuals, worth every penney.

Regarding your problem : First thing I would check would be the catalytic converter. I think your truck, just like mine, has the oxygen sensor before the cat.. just remove it from the hole and testdrive it. The idea is, if there is too much backpressure from the bad cat, opening the sensor hole will relieve it. If you get your power back, then it is the cat. If not, I have other ideas, but thats where I would start. I have seen and read about too many perfectly maintained older trucks lose power because of a bad cat... check it out first.

 

Only downside to that is my o2 sensor wouldn't be reading properly. I think I'll just get it pressure tested. Someone told me they had it done for $10.

 

Your O2 sensor will not be reading at all, as you will have to unplug it when removing it, so it does not dangle It is not a big deal though. Just drive it around the block, if the power loss was due to cat it will be apparent immediately, you will have your power back. Then just install and plug in the 02 sensor and reset the codes.

 

I have the exact same problem ever since I got my 90 4 runner...I get passed by 18 wheelers going uphill, thats pretty bad! When I get back from my honeymoon I am gonna remove the 02 sensor and see what that does...

 

I removed the o2 sensor on my 91 and like you guys were saying it was as soon as I started down the street that you could tell it made a huge difference. I'm thinking I've got the same prob...what cat should you replace it with?

 

The best I can tell, any new cat that is specified for the vehicle will be sufficient. The lowest priced stainless steel cat of proper size will last probably for as long as you going to keep the truck.

If you want to squeeze the most performance out of it, get a freeflow cat from a good brand. If you feel like spending another $150 on top of the cost of the cat for a little bit of additional highway performance, get all new 2 1/4 piping and muffler all the way from the catalytic converter back to the tailpipe.

The advantage of doing it that way, at least on our older trucks that have all the pipes rusted together, it is a little cheaper to do it all at once, cat and the pipes and the muffler because there is less welding to do. If you do just the cat with the old pipes, they will have to weld them to it more likely than not. Thus if you later want to put in 2.25 pipes and muffler, they will have to reweld it to the new cat. Do it all at once if your pipes and muffler are about to go anyway.

The ultimate way to go is stainless steel pipes all the way, but that pretty much doubles the cost of parts. So your problem could be solved for $120 you are on a budget, or you could spend up to $500 on cat+ stainless steel exhaust upgrades.

 

Help me understand this... The engine uses codes read from the o2 sensor to operate. If it's unplugged it's not going to run properly. How are you going to know whether your issue is with the o2 sensor or the cat? Case in point, my o2 sensor died a couple months ago. To test it I just had to unplug it and my truck ran better. Forget the fact that I know my o2 sensor is good . Let's say I didn't know. How would I know which was causing the issue? A plugged cat or a bad o2 sensor.

And on the other note. What about the missing? Just on my way to work today it missed... I think twice. Once at about 35 mph. And another time at 70mph on the freeway. Both times it just felt like a stutter.

 

Also check the TPS. While I don't think a huge power loss is usually a symptom, hesitation is. You should be able to disconnect it and drive but it will throw a code. Test it out and then just pull the EFI fuse for 10 minutes or so.

You can also check it with an ohm meter. Here's the page with all the info on it:

http://4crawler.com/4x4/CheapTricks/TPS/index.shtml

The symptoms of a bad TPS are at the bottom.

:bounce2:

 

My timing changes when I'm jumpered. I'll check for buildup but I believe my TPS is working properly.

 

TPS on these friggin things are tricky. Look up some of my posts to see what I just went through.

Regarding the 02 - your huge power loss, if it comes from the catalytic converter, will never be equalled by anything that your 02 sensor can cause. So, if you unplug that hole, even when the 02 sensor is not giving the engine the proper readings, you will know if plugged up cat is your problem. Your power should be back, even though it will not be running perfectly without the sensor. It is kind of like a banana in a tailpipe situation. Any restriction in the exhaust beyond what has been designed will lead to bad power loss. If you drive it down the street with that hole open and feel the huge power loss is still there, then it's time to look elsewhere.

 

Hmm... I'll pull it when I leave work in half an hour. Test it on my way to class. And post from school whether it worked or not. I hope I hope I hope! If that's the case I'll just remove the cat and put a straight pipe in. Kinda nice living in an area with no smog restrictions.

 

carsound freeflow cat is only $56 shipped. I got one and it works great!

BTW - something usually causes them to go bad. Usually running rich or bad O2 sensor (though you should get an engine light)

 

There's lots of things you should get with OBD1.

 

lol. Yeah, I'd expect CEL with the way it's been running... but no. So I didn't get a chance to unbolt the o2 sensor. I just have a pair of pliers with me and need a socket. I'll for sure unbolt it when I go to work after class.

BTW, I'm noticing that since I played with the timing I've regained some power. I think my main issue now is the somewhat rough idle, the occasional hesitation, and just a little more power. Oh and what is this smell???? It smells musty or like BO but I'm smelling nice and fresh! lol. Just about when I got to school I could smell something funky. And it isn't me. Hope I don't have some moisture in the cab.

(posted via an unsecured wireless router accessible from the college's parking lot )

 

Thanks T...I'm wondering if it's running rich. I just put on a new o2 sensor..It hasn't any exhaust work done in 230,000 miles! I thought it should probably be done...how do I know which cat to order on the site....I was planning on switching to 2 1/4 pipe. I don't know what the pipe is on there now, but I wanted to try and get a bolt on to replace the cat now and later get a muffler and maybe some headers. Thanks for the help

 

You currently have a 2" but if you ar going to 2.25", then get the 2.25". If you know anyone who can weld or are going to have a shop put it on just get the universal instead of the bolt on. Then cut the flanges off the old one and weld them to the new one. Then you have a bolt on that was a lot cheaper! I'll try and get a shot of mine and post in this thread tonight.

 

I wish you would not. Would you dump used oil on the ground if it was allowed? Do us all, and your children (or future children) a favour - keep the catalytic converter on. It is there for a good reason, and when properly functioning a freeflow cat will not impede your performance but really cut down on pollution. There is enough crap in the air to breathe... Nice living in the area with no smog restrictions? I guess what you don't see can't hurt you .. or can it .. Just go to www.howstuffworks.com and read what catalytic converters do.. hopefully you will not consider it a useless annoyance anymore.

 

hey, trunner...thanks for all the help and I'd love to see the pic. Which of the $56 ones on carsound am I to get? There are a couple with 2 1/4 so I'm kinda confused. Sorry, I'm just diving into the exhaust thing and trying to do as much research as I can along the way. So is the cat 2" in and 2 1/4" out? Thanks again