cronos

Hello
98 cherokee 4.0 5 speed, 170K miles all stock
The power loss was pretty sudden and i think it took place after the engine was washed down (salt)
idles fine, gas mileage seems about the same (15-18 mpg). throttle response is good, no dead spots or rough spots.
reading no codes.
new down stream O2
tune up recently, new plugs and engine gets good spark all plugs.
distributor and rotor cleaned
cleaned plugs and sensor connectors (didn't test any sensors)

I hoping to find an order that the forum would go through to test the power drop.

Thanks in advance.

coastie903

Take a look at your TPS (throttle position sensor) they tend to act up when wet...

cronos

replaced the TPS, same result.
Feels restricted with no roughness.
looking for advice on what else I can check.
Showing no codes nor stored
Thanks

tjwalker

1. Gotta rule fuel pressure in or out early in the process. For a 98, you should have 49 psi, plus or minus 5 psi. A fuel pressure gauge can be rented from many parts stores; call around.

2. Clogged exhaust (catalytic converter) can be tested with a simple vacuum gauge. Is this an original cat?

3. Never hurts to get compression test readings on all cylinders. A good snapshot in time of the internal condition of the engine. For the 4.0, you should have 120-150 psi, with no more than a 30 psi variation between cylinders.

cronos

Fuel pressure was 50 PSI
compression was between 148-160 between the 6 of them

where would i test the back pressure for the exhaust? A back pressure gauge at the O2? I checked Autozone for a loaner but they don't have one. An alternative?
Also I have seen tests with a laser thermometer on the cat comparing the temp. Don't know if that is an accurate indication?
Thanks in advance!!!

tiwvr1

Try shifting manually. or drive it and see if its stuck in third. Could be TCM

And for back pressure u can pull the front 02 out and drive, it will be loud but if its the cat you will notice a big diffrence.

cronos

Its a 5 speed trans
checked vacuum on manifold with my mighty vac- got 18 inches. Vacuum seemed fine, blew rag out of exhaust as well.
the cat is original with 173K
i'll pull out the upper O2 and see what happens...

Radi

Steady, not dropping over time? A plugged cat will cause vacuum to drop off right after the motor starts. The more the drop the worse the clog. As mentioned, unscrewing the front O2 will create a temporary hole before the cat, you'll notice a big difference if the cat is blocked.

What happens if you rev the motor, hold it, then let the throttle snap back to idle?
(you should see a sharp vacuum dip when you initially rev it up, vacuum should come right back up and hold steady once RPM stabilizes- no jitter- then spike slightly and settle right back to it's previous idle value and hold there when you release the throttle.

Where did the new TPS come from? I'd check the output voltage anyway, bad parts out of the box do happen from time to time. Measure voltage at the center wire, key on engine off. Should be rise to just under 5 volts in a smooth, linear fashion as you rotate the throttle open by hand.

cronos

TPS was from Pepboys or Autozone. Drove same (old to new TPS)
O2 is a b.... still not out. Its been heat up and DP blasted
The video shows the vacuum gauge.

cronos

Took a laser temp read of the cat and it read about a 100 degrees hotter at the exit.
Could it give me a working reading if it was clogged?
Also noticed that there was a rattle coming from the cat.

Thanks in Advance