Rithsleeper

I know it's long but please help, I'm a pretty good backyard mechanic but I'm about out of ideas.

So about 10k miles ago I started hearing this little almost puff coming from my exhaust. I've got a hole in my muffler (no holes north of the muffler so the O2 is not affected) so I can hear the engine better than most.

This sounded like if you say the word "put" but just the puh of the word. At first it was about every 3 or so seconds and very small (no one would notice but me) then it gradually got more consistent. Only happening at light throttle cruising (not idle or acceleration). I thought, hey, with a 1994 and 150k miles, prob a vacuum leak. Did the starter fluid test and inspected everything with a vacuum manual pump taking off each line and all are surprisingly good shape.

Hmm so I think what do my plugs look like? Car feels like it's running ok. Well plugs look a bit lean but nothing alarming except 4th cylinder looks slightly sooty and think we'll there it is, rings are bad in #4. I was getting an exorbitant about of blowby in oil cap so I thought well I'll just do a rebuild before it gets too bad. Had to wait a few months till summer though. Problem gets louder and more frequent now happening in all rpms.

Rebuild goes well and find a seized oil ring in #4, think, "There is my culprit!"

During rebuild find the engine in extremely good shape no need to bore cyl, no cracks on head gasket, just really everything surprisingly clean. Get valve job and everything. Only thing I don't replace were the injectors (I have those on order and will replace tomorrow).

After rebuild I seated the rings and have driven about 100 miles when I heard the sound for the first time yesterday. Same as it started before. Small and subtle....

I have done the following, thinking this was the problem with no effect:
1. Swapped #4 injector with cheap aftermarket
2. Changed plugs, wires, coil (plugs now iridium)
3. Checked all vacuum for leaks
4. Changed O2 sensor (figures it could just be old)
5. Checked for exhaust leaks before O2 sensor
6. Complete rebuild with valve job
7. Changed fuel filter in rebuild
8. Valve adjustment both hot and cold no change
9. Rechecked idle and timing, new timing chain.

Next steps, in order:
1. Replace injectors and check fuel pressure by tapping the fuel rail
2. Eliminate all emissions and cat converter (would rather not but at this point need to eliminate that as a possibility (no emissions on SC)) would this cause a CEL? Seems like easy to eliminate all but FPR and AC idle step
3. Replace distributor (maybe worn points? Not sure why rebuild would have made it better)

The rebuild did fix the blowby and engine idles very smooth now. On acceleration it feels ok but just like there are a couple of cylinders that are half power from time to time. No misfire but not super smooth power when accelerating.

I'm at a loss. Only other thing I can think is camshaft lobe worn but it all looked perfect on disassembly and why would that cause that sound?

Puh, puh..... Puh puh puh. Puhpuh. Puh, puh

Melrose 4r

Have you readjusted the valves? The puh puh puh in my experience is a burnt exhaust valve but your valve job should have addressed any. Readjust exhaust valves making sure they are not too tight and see what that does for you.

Rithsleeper

I adjusting them cold on initial rebuild. .008 intake and .012 exhaust. Then after sound came back I went and adjusted them hot after driving .009 and .013 (like it says in my manual and they were all pretty darn close only had to adjust 1 a tiny bit). Maybe I can go back and give the exhaust till 0.14?

Rithsleeper

So I tested fuel pressure. 44 with no vacuum and/or car is not running, then 38 with vacuum. So more perfect than I could have asked for for that old of a truck. it keeps pressure for hours afterwards. I replaced the injectors with a set of "MOSTPLUS" off ebay since they were $50 a set. The car actually runs a little worse now. Hesitation throttling up so when I finished that job, I thought oh good! It must be fuel pressure related and my old ones were leaking or something. Nope.

So I cut the catalytic converter off and I think it was replaced at some point since it was fine too, not clogged but still replaced it with a pipe so I don't need to worry about it. Still not difference but now the truck is louder.

I went back and checked the valve lash hot this time, everything is in spec, one was a bit tight so I took it out some but no change. Checked timing again, all my vacuum lines to double triple check, reset idle adjustment. Still the problem persists, but now I have more hesitation on the acceleration. The plugs look ok, but Cyl 1 looks lean and gradually gets to perfect by Cyl #4. This is exactly how they looked before the rebuild but Cyl #4 was super black because of the frozen oil ring.

Checked again for another exhaust leak which I can't find one, I should be running rich. I taped up my shop vac to the tailpipe and turned it on, then used the hose in my ear trick to check for leaks and found nothing. which should also find leaks in the intake manifold since it's putting vacuum on the manifold which I put tape over the TB also.

I would say that a manifold leak could cause a lean condition, but I just tore the manifold apart 3 times and no signs of leaking and sprayed it with starter fluid and no change in the idle.

I'm really at a loss. OBD1 is so primitive. As far as it's concerned the engine has never thrown a code and the dash light works when I start the engine.

I tempted to just buy a microsquirt since I run a MegaSquirt 3 on my corvette, and just tune the problem away. Just tell it to run a bit more rich.

Only thing that could be noted is that now it gives big puffs on engine braking that it didn't before, but that could be these injectors or the cat being gone.

My next step is to eliminate all emissions crap. Maybe the EGR is stuck a little open or the Air Exhaust system is messing up.

Melrose 4r

Can you do a compression test on it to make sure its not a valve?
But You seem to describe an intermittent power loss. That has to be fuel or spark. Several people have experienced intermittent injectors due to poor splices in the factory injector harness. Hope you get it solved.

Rithsleeper

Compression test was within 4psi, injector wiring could be a possibility however I would think the injector not firing would cause a more blaintant result. This is super subtle. Like a passenger wouldn't even notice it. I'll go and put a meter on the continuity and wiggle them around good and see what comes up. Going to eliminate egr Tuesday when parts come in.

thefishguy77

iTrader: (1)

When I rebuilt my 85 22re I was having a similar issue before rebuild but mine was a super minor cutout. Rebuilt the motor and she ran great for about 300 miles. Then the cutout came back but got worse. Finally it wouldn't run more than 30 seconds before dying but sounds perfect for those 30 seconds. Well now there was 3' of snow on the ground and I have no garage so off to my buddies shop it goes. Turns out I had a broken injector wire inside the sheathing. They fixed it and its been perfect since.

Probably finished breaking the wire when I reinstalled the motor and it just showed up a but later.

Melrose 4r

I recently disabled the egr on mine per the old whitepaper TRD published in the 90’s. All you have to do is plug the vac line leading to the diaphragm with a BB. The engine is noticeably more responsive in certain rpm range. I thought gas mileage would improve but it didn’t change.

Rithsleeper

As far as the injector splicing, how far back does the problem go? Is it right at the connector so if I buy a new set of pig tails and splice them in nicely about 6 inches back from the connector they would be fine? Or do I need to go much farther back? I'm betting they make a kit for it. From your discription, that could be the original problem, but not sure why I would have fluctuating power with new injectors...

As for the EGR, Im more worried that the valve is stuck barely open and plugging it would just keep from engaging completely but not keep from disengaging. I had a bad misfire when a wire started arching about a year ago and I'm convinced that's what froze the oil ring with carbon build up. But in my experience with Chevy's and Mazdas, egr valves hardly ever fail that way. But at this point anything is possible.

Thanks for something, I'll continue on my path and update when I finish stuff.

Melrose 4r

You can block off the egr at the plenum with a scrap of aluminum from a coke can.

i once had one stuck open on a 20r Celica. It was way down on power, ran crappy. Basically undriveable due to the big vac leak.

You seem pretty “old school” like me. Do you have a vacuum gauge?

Rithsleeper

I do have one of those brake bleeders with the vacuum gauge on it. I usually just use it to see if there is vacuum, don't trust it to tell me accurate numbers about how much. Are you suggesting manually opening the EGR to see if anything changes or something? I've got the block off plates coming in the mail tomorrow with a 10k ohm resistor (can't work on it till then anyway)

Melrose 4r

The quickest test for the egr is to just apply vac to it by mouth and see if it opens or while running to see if the engine stumbles. What i was really getting at with a vac gauge is to monitor its behavior while running to see if it reads steady or fluctuates in a certain pattern when you hear your puh sound. Its a diagnostic tool most on this forum don’t seem to know about...only us old guys with carburetor experience on old cars.

old87yota

A vacuum gauge for vacuum systems is like a multimeter for electrical systems. They are pretty essential for diagnosis.

mbomberz1

It might be worth double checking your throttle position sensor and your vane airflow meter. I can't remember the tests off hand, but I know you should be able to check voltage. Its possible one or both may need some attention, if your not getting good info to the computer, they can give you issues too. I only suggest it since it looks like you have taken care of nearly everything mechanical. Good luck!

coopster

Hey OP. What was the outcome?