blackbird70

Hi all. New to this, but I've read through the forum and can't quite see my issue. Long sad annoying story short:
We've got a 1994 3.0 v6 Forerunner automatic. Over the last week, the mighty car (mine, now my son's) has been losing power to the extent that accelerating now you can't get past about 80kph (50mph). This is across the gears. It changes smoothly enough, idles fine etc, but has no power. Going up a mild hill is a struggle and it slows down to about 30kph/20mph.
So far we've put in new 02 sensor, new TPS (got to recheck we got it set right), new fuel filter and pump, new distributor cap and rotor and new Mass air filter sensor. All no real change. New plugs too. Pretty sure its not the catalytic converter as my son knocked the centre of that out to give more low-end power, and he did that ages ago.
Options - could be the timing belt is out a notch? it is old... but changing the belt that is a big job and I'd have thought if that was the problem would be sudden onset whereas this has been more gradual, then increasingly severe.
Symptoms don't suggest blocked fuel injectors.
There is a slight hole in the exhaust but again, wouldn't have thought that was it. maybe the exhaust is blocked somehow?
I reckon its got to be poor fuel/ air mix or problem with exhaust, but like I said we've done almost all the fuel/ air mix troubleshooting...
We're at a loss. any advice appreciated very much. Need it fixed ASAP as he has to go start a new job.

fdp101452

Run a compression check bet you’ll find a cylinder or two down. Probably a tight valve probably 5 or 6

blackbird70

sorry, should have mentioned we did a compression check on cylinders 1,3 and 5 and they were all 150 psi... Mechanic didn't check the other cylinders though...

akwheeler

you need to go to a different shop. That's just plain lazy. a proper compression test REQUIRES all plugs to be removed and you might as well test all 6.
Check timing, check compression, fix any exhaust leaks upstream of the O2 sensor AT LEAST.

blackbird70

Thanks, I did discuss with the mech and he reckoned if 1,3 and 5 were ok the others probably would be but I agree we need to check them all.
Going to check timing tomorrow and vacuum hoses.
Appreciate the ideas, keep em coming!

akwheeler

1 3 and 5 are all on the same side of the engine, if you paid them for a compression test you need to go somewhere else.
there could easily be issues on the other side with valve clearances or rings or even a failing head gasket that would show up as low compression in one or more of those cylinders.
if your timing jumped on that cam ALL 3 cylinders would show low compression.
It IS likely that it would be running rough, but you have to start somewhere. Kinda like a doctor taking your pulse and checking your temperature.
you need the whole picture to get an idea what is going on.
If your "mechanic" is the one who recommended firing a parts cannon at it and replacing everything he could think of before actually diagnosing what is going wrong he owes you an apology and a refund.
If it was your idea I apologize.
the way you described the symptoms I could easily see it being several other issues, like brakes dragging. so we need more info and you need to eliminate possibilities without throwing your wallet at it before finding out the transmission is shot.

blackbird70

Hi again.
You're right about the compression test and I'll follow it up with him.
He didn't recommend all the work we've done, we're basically trying to eliminate possible causes as no mechanic has been much help to date. Few seem to be familiar with old cars here in Perth...
Current idea is some vacuum hose failing....sound likely?
What would be a rest for dragging brakes?

akwheeler

Dragging brakes will build up a lot of heat when you drive and you will smell something burning similar to burnt clutch smell.
If you get up to speed and put the truck in neutral and it coasts freely then it's not brakes dragging.
for vacuum leaks you can take an unlit propane bottle and point it at different areas of the engine compartment around the vacuum lines.
if you are near a leak the engine will rev up. Just keep away from the distributor since that is literally throwing sparks around inside.
A very likely spot for a leak is the intake boot right at the throttle body.
Most vacuum leaks will cause you to have a high idle unless someone had monkeyed with it.

blackbird70

So... Still might be the vacuum hoses. But the fuel lines appear clear. Took off a line near the fuel pressure regulator and it was pumping fine. Also dumped half a bottle of injector cleaner in the tank.
Now it's revving OK and will behave more or less normal but will not go past 80kph. Just refuses no matter how much you push it.