dawa88

Ive got an 89 pickup that I bought a few months back and have had nothing but issues with it. Previous owner did a very good job hiding all its problems before I purchased it. Ive worked through most of the issues and now its onto the fuel efficiency. Engine is a 22r with EFI and I currently get ~14mpg or 16-17L/100km (highway or city, doesnt matter). Im pretty sure the O2 sensor needs replacing, but Ive also just been told having no catalytic convert = no fuel economy, which is the opposite of what I previously thought.

So my question is, will removing a cat decrease or increase fuel economy?

j2the-e

It may have some effect. But shouldn't be that noticeable.

jalopytech

I'm doing 17 with no Cat. 91/22RE, 235/70 tires.

Hilux808

To answer your question...yes. A free flowing exhaust with less back pressure always helps with power and MPG's, especially on the high end like freeway driving. Although simply removing your CAT and doing nothing else might not be that much of a noticeable difference. Assuming everything else on your truck is running good you would really benefit from a full exhaust system with bigger size pipes. That one mod alone on my 4Runner and Frontier really boosted highway MPG's for me. On both trucks I have a full Manifold back exhaust with no CAT, 2.5" tubing and Magnaflow mufflers. I plan to get headers sometime in the future for my 4Runner, this should give more improvement too.

I'm not to familiar with the 22R but it sounds like you should be able to get a little more out it. I have a 91 22RE with a full MSD Digital 6A ignition, this helps me to get over the stock rated 21 mpg on the freeway and I'm running 31" tires.

Fuel economy can be affected by many issues. People who drive like drag racers will have poor fuel economy; driving style is one of the biggest factors when it comes to have poor MPG. Thoroughly check your truck out first to make sure everything is working properly. Check your air filter, tire pressure, replace your O2 if it is bad or past it's change interval. Is your idle speed adjusted properly or is it running higher then it should? Ignition timing, Spark Plugs, Spark Plug Wires, Throttle plate valve/TPS adjustment, EGR, PCV, Thermostat, Coolant Temp Sensor, Valve Clearance (especially if too tight) should all be checked, to name a few. Do you have bad fuel injectors or a bad fuel pressure regulator? Is your fuel filter partially plugged? Running synthetic oil can
really help with more then just MPG's.

Hilux808

sorry...2.25" tubing on both trucks. Going too big isn't good either when it comes to exhaust.

dawa88

Awesome, thanks for the input! I have done a bunch of those things, the exhaust was redone before I purchased it, Im pretty sure its 2" with a flowmaster glasspack muffler. Ive done the spark plugs and wires, tires are in good shape running proper psi, brakes have new pads and have no rub, cleaned the throttle body (which was super dirty), idle is good, and Ive got a new air filter.

The head gasket was done with a remachine of the head new water pump recently, but afterwards the shop couldnt get it into base timing mode, so timing is still a concern. The reason Im doing the O2 sensor next is because the previous owner was a hack and upon inspection noticed that only one bolt holds it on, it clearly isnt sealing to the pipe and unfortunately he decided to save 20$, chop the connectors and solder on a universal...

Hilux808

You need to fix your timing issue first. You're either one tooth off on the distributor or the timing chain could have been installed one tooth off. Check the distributor first, get a repair manual if you don't have one, this could be an easy fix. I recently installed a new distributor and I was one tooth off, could even see the timing marks so I knew something was wrong. I turned the crank back to TDC and reinstalled the distributor, all is good now.

jalopytech

When you say "the shop could'nt get it into base timing mode". Do you mean when they jumper the diagnostic connector the timing did not change? If so I would be interested in the outcome of this. I have one that when jumpered the check engine light flashes but the base timing does not change.

dawa88

honestly my knowledge of engine operation isnt extensive, so really Im not sure. Its a long story, but the shop had to do the head gasket in a short period of time and the evening I picked it up they told me it wouldnt enter base timing mode and that after driving it for a period I may need to retard the timing by rotating the dist. cap in slight increments.

jalopytech

That's what I thought you were describing, I'm interested in the outcome. I have one with the same problem, I know my diagnostic connector is jumped correctly because my check engine light flashes the code all is OK, while jumped.
Thanks

dawa88

Ill let you know how it goes this week!

JohnnyCanuck

If your o2 sensor is shot, your ecu defaults to rich burn. Once you get your timing issues sorted, meter your sensor out to ensure its working and if it's isn't, replace it with a Denso unit...good luck!

jalopytech

My thoughts to all this is and goes along with thoughts of sensors that have failed such as this. And not thrown a code. So if one could remotely control fuel control (rheostat), inline with the Intake Air Temperature and MAF sensor & Oxygen sensor. Trick the ECU into thinking the intake air is much more cooler, then the ECU would send more fuel for a richer mix, And override the oxygen sensor. You could then adjust the Air Fuel Ratio. This would Remap the ECM to any performance exhaust, intake, ratios, etc.. installed. And would modify signals being read by the ECU and would not allow the ECU to restrict the air/fuel ratio because it has been fooled. Efficiency of combustion is improved (power) and you could even SAVE FUEL.
I'm outside the box again....I better climb back in.

highonpottery

iTrader: (1)

buy a new o2 sensor. Amazon has Denso sensors for pretty cheap compared to everyone else. while it's in the mail, work on your timing. my guess is they had it off one tooth as well that's why they couldn't get it to work. if you search for the 93 Toyota FSM you will see the proper procedure for timing. cheap timing light can be had at Harbor Freight for like $10.

you should be getting better MPGs once you work on those. as to the CAT question, it doesn't matter really if you have an aftermarket CAT since you can see right through them vs the stock ones that are diverted through a baffling system (like a regular flowmaster muffler is). my truck was getting around 18mpg hwy, but then i just upgraded my exhaust from downpipe-back and i definitely picked up at least 1-2mpg, and more power.

wvtoyboy

cutting off the Cat will do nothing more than reduce back pressure, resulting in better top-end performance... however, it will do littl to nothing for bottom-end...one common mistake is running too big an exhaust with the idea that less back pressure the better (great idea for diesels and race cars that run wide open all the time), but not so great for gasoline engines. Ideally most 4 cylinders should run 1 7/8 for stock engines and 2-2 1/4 for modified engines to keep enough back pressure to provide the optimum power

AdmiralYoda

I second this. But even then, by modified.....more so than most people think. 2.25" is good for all the bolt on's. Intake, AFM, header, high flow cat and muffler, larger/better head, and larger/better cam.

For the "modified" engine with just intake and exhaust done.....2" is perfect.

Its all about maintaining exhaust velocity. Exhaust cools down as it reaches the tailpipe, and when it cools down it slows down. You want to keep it hot so that it can get out as fast as possible. This preserves the scavenging effect which is so important for low end torque.

If you make the exhaust too big you lose backpressure, lose scavenging, and lose torque. You do make it up on the top end though. So if you are doing drag racing or dyno runs.....2.5" all the way back.

Here is the best combination of sizing to get the best balance of torque and horsepower gains and maintain exhaust velocity.
- The header collector is 2.5". Put a 2.5" pipe to a 2.25" catalytic converter.
- From the 2.25" catalytic converter put a 2.25" pipe to a 2.25" muffler.
- Then use a 2" tailpipe.

If you have a head and cam done......go 2.5" all the way to the muffler, then go 2.25" through the tailpipe.

The exhaust system can only flow as good as its smallest point. You want that smallest point to be your tailpipe.

BTW......just in case anyone is wondering....I'm talking mandrel bends, not press bent stuff.

jalopytech

Correct!

snobdds

But...if you cut off your cat and have no back pressure, how do your valves close fully?

snobdds

Double Post.

j2the-e

I hope this question is meant to be sarcastic...never heard of a correlation between exhaust size and valves closing