bgreenlee

Picked up a '96 4Runner a couple of months ago from it's original owner. It has 140k miles and has been supercharged for the last 80k of them. No fuel mods.

It seems to run fine and I haven't detected any audible pinging in the couple of months I've had it, but I'd still like to get it setup correctly with the URD 7th injector kit and go ahead and go to a 2.1" pulley while I'm at it.

Since the s/c is at 80K miles (1st gen), I'm considering going ahead and having it rebuilt.

Before I dump a ton of money into it I wanted to make sure the motor is in good health- especially since it's been run for a long time without any of the fuel upgrades.

If it's not in good shape, I'll refrain from putting any money into it and just run the motor until it blows. But if all is well, I want to get it set up right for good.

Did a compression test this previous weekend and came up with these #'s:

#1: 200
#2: 195
#3: 175
#4: 195
#5: 195
#6: 195

Obviously an outlier on cylinder 3. Recommended #'s are supposed to be 175 with a maximum cylinder difference of 15, however, all of my cylinders are around ~195 with a single one 20psi less.

I know cylinder 3 would also be where I could expect to see cracked heads if that were the case, but I don't seem to be losing any coolant and I would imagine the psi would be much lower than 175 if there truly were such an issue.

As a test, we dumped a capfull of oil into cylinder 3 and tested again. It came up to 185psi. This also seemed inconclusive to me- came up a bit, but not enough to directly mean much?

My #'s don't seem actually bad to me, but I really wish #3 was 5psi higher or so - would have gone a long way in making me feel more confident about dropping the money in it and meaning the engine really was in great condition to start with.

In any case, what do you guys think? Anything to be concerned about?
Or should I just keep an eye on it and dive into getting the fuel mods done, getting the s/c rebuilt, and upping the boost slightly....

HighLux

did you do it cold? did you do it with all plugs out and throttle wide open?

bgreenlee

Warm engine and all plugs out with wide open throttle.

Kiroshu

Well considering cylinder compression for the 3.4 5VZ-FE is:

-218 PSI Standard

-145 PSI Minimum

I would say those are pretty healthy numbers considering mileage.

The wet compression test you performed showed that some of the compression loss is through worn piston components and or cylinder bore.

The lowest cylinder reading is 10% less than the highest cylinder reading which is ok.

Anything more than 15-20% difference is highly noticeable, usually by the engines performance, and obviously not acceptable.

HighLux

I think you are ok. Its got some miles ya know?

This is a case of its not broke dont fix it.

one slightly weak cylinder does not necessitate (sp) a rebuild.

bgreenlee

Thanks for the responses! It does help re-assure me. I know the numbers aren't necessarily "bad", but that one cylinder being down 25psi from my highest one did give me a bit of concern.

Is it strange that it's so localized to one cylinder like that?

Also, I should clarify that the rebuild I mentioned was a rebuild of the supercharger not of the engine itself. Just wanted to make sure the motor is all good to go before having the s/c worked on and potentially upping the boost a bit with the 2.1" pulley.

Thanks!

HighLux

I dont advocate turning the boost up...lol. I think the blower is more than likely the cause of the lower compression cylinder. I wouldnt beat on her too much. Maybe make the boost you are making more efficient. Intercooler and some meth injection.

vital22re

iTrader: (2)

Do not jump up to the lower pulleys unless you're ready to sink up to 2k into it. factory should be 2.3 but some dealers installed a bigger pulley to compensate for the ping. I'd rather leave it as is and just run a methanol injection kit with controller.

bgreenlee

I should have said 2.2" pulley instead of 2.1".

BUT I'll skip doing even the 2.2" pulley if it really seems like a big risk take. In that case, I am still going to have the s/c rebuilt and do the urd 7th injector since these two things should be done anyways. I just didn't want to spend on the money on doing them if the consensus was that this engine might be on it's last leg anyways.

Any chance that 80k supercharged miles without the proper supporting fuel mods could be to blame for the #3 issues?

Again, I haven't heard any audible pinging- even when I've tried to force it to test with high gear / low rpms / heavy throttle, but I've only owned the truck for the last 1k miles. (I realize damage could be done even if the pinging isn't audible.)

HighLux

I know from personal and exspensive experience, that if you dont have enough fuel on a blown motor.....it will reveal itself very quickly and with catostrophic results.

I think its just from the extra cylinder pressure over the course of alot of supercharged miles.