Help please - my mechanic is stumped (2 Viewers)

[Quailhunter]

I use a local mechanic for my 93 FZJ80. He focuses on electrical and can do full service. Seems to be skilled and honest.

I took the car in with dummy lights and little power. Could hardly make it up the hill to my house. Codes for oxygen sensors so we replaced those with Toyota parts. Still running poorly so we did basic tune up stuff. Replaced PCV valve, plugs, wires, fuel filter, still not running well.

Seems to be excessive vacuum in the crank case through the breather hose, not the PCV. Whoosh of air when the oil filler is opened and the engine nearly dies. Checked all of the air input stuff and nothing seemed to be clogged. None of the sensors or contact points appear dirty. No apparent external vacuum leaks.

Timing seemed off, he has adjusted a bit without noticeable improvement. Seems to have a slight miss on all cylinders at low speed that can be felt higher RPM. Maybe idles a bit high when cold.

He is at a loss for what to try next. Has looked at the usual professional advice sites and there are several ideas but nothing conclusive. Any suggestions for how to proceed?

 

[Fosters]

Oil and coolant levels good?
Cylinders pressure tested?
Smoke test the intake ?

 

[ppc]

Timing seemed off, he has adjusted a bit without noticeable improvement. Seems to have a slight miss on all cylinders at low speed that can be felt higher RPM. Maybe idles a bit high when cold.

Timing should be verified/set with a timing light and set to the factory specification of 3 degrees BTDC. If he does not have a timing light then find a new mechanic. I find it hard to believe that even the best mechanics could determine a slight miss on all cylinders without using a scope. Yes, a miss on one cylinder can be determined by unplugging each spark plug wire one at at time. High idle on a cold motor is perfectly normal. The idle when warm should be 650 RPM. The statement about high vacuum is again is ambiguous. When opening the oil cap the engine should stumble and is perfectly normal.

 

[SmokingRocks]

Woosh of air out or in? The case is designed to be under vacuum at idle, the intake manifold sucks air out of the case through the PCV valve. If you open the oil, cap and air rushes in, you’ve created a massive vacuum leak for the engine which will cause it to almost stall. This is normal operation.

 

[cruzinfj1]

Plugged CATS

 

[Rusty Marlin]

Plugged CATS

Having had two different vehical's cats disintegrate and plug the exhauts, there's a distinct possibility based on the description.

 

[PIP]

Check egr valve is not stuck open.

 

[Quailhunter]

Many, many thanks for replies. Will continue the diagnosis process tomorrow and report back to the curious world.

 

[Mark W]

Keep in mind that the engine ECM really has no idea what the fuel pump is doing. It assumes appropriate fuel flow/pressure and any codes it may show will be secondary results of not having this *if* the fuel is not sufficient ("misfires" for example).

If fuel flow is so low that you have a rough idle, I would expect that the rig would just barely get out of it's own way are any higher rpm if it was due to a clogged filter. A failing pump *might* keep up a bit better even if it is already showing symptoms at idle. Do not ignore the possibility of clogged feed lines or fuel pump "sock" (inlet filter) either. I have also seen this a couple of times.

Anyway, make sure your fuel flow/pressure is correct. From what your description of the symptoms are, I would definitely check this possibility before you wander too far into the weeds searching for other problems..

Mark...

 

[greentruck]

It's worth rechecking the big rubber air intake tube. It's easy to miss a crack in it and an easy fix if it turns up.

 

[NorCalFJ100]

Check your cats x3

 

[flintknapper]

Agree to carefully check the air intake tube (from air cleaner to engine) and then CATS/exhaust back pressure next.

 

[JOFS]

catalytic converters is my vote

Good luck
John

 

[mudgudgeon]

Check every possible vacuum leak.
All the small rubber hoses. Checking for hard, cracked hoses, or hard deformed ends that no longer seal or clamp down tight
Loose or missing vacuum hoses under the manifold?
Main rubber intake hose, cracks in the folds?
PCV hose and grommet. Check for cracks. Check still soft and pliable?
Oil cap seal? Soft and pliable, or rock hard?
Dipstick seals.

My experience with bad cats is the problem shows after the vehicle has been running for a while, and shows up more when driving vs at idle.
That's not to say it can't be cats

 

[CharlieS]

I'd get a better mechanic.

If you're looking for vacuum leaks, consider a smoke test. I'd hope a pro shop has a smoke testing machine. I find that a very useful tool for identifying vacuum leaks. There are so many places that you can get a vacuum leak that you might miss if you do anything short of replacing every rubber hose, line, seal, gasket and o-ring (and there are so many!). I keep on finding new rubber parts that are potential leaks. One example is that I recently found leaky injector seals. You can get a setup for under $100 - I've used mine to find leaks on multiple vehicles.

 

[vipergrhd]

I will just suggest check fuel pressure and fuel quality as well. I also vote for the Cats being clogged and check what kind of vacuum reading you are getting at idle and WOT.

 

[flintknapper]

I will just suggest check fuel pressure and fuel quality as well. I also vote for the Cats being clogged and check what kind of vacuum reading you are getting at idle and WOT.

^^^^^

Easy to check with a simple Vacuum Gauge.

Should have around 20 inHg at idle (all accessories turned off).

 

[cruisin4bruisins]

My first guess would be a fuel issue (failing fuel pump or clogged filter) or catalytic converters. Id do fuel stuff first because its cheaper.