86longbed

I took my 86 pickup in for an emissions test, which it failed. For some time I'd been getting a small, intermittant miss when the engine is revved up, and my HC's were over the limit during the rev portion of the test. Upon close inspection I eventually noticed a small vacuum leak sound coming from the EGR valve. I checked for a leaking diaphram by applying vacuum to the port on top and it holds steady at over 20" of vacuum. I pulled the valve and then tried blowing into the pipe fitting to see if it was seating properly. That's when I heard air coming out through the holes where the diaphram is. It's very little air, mind you, but it's audible when blowing very hard into the pipe fitting. No air is coming out the other end of the valve. I tried blowing into a spare EGR valve I had lying around and it has the exact same tiny leak. What I want to know is whether this miniscule leak is enough to warrent spending the $200 on a new EGR valve? Is it most likely the cause of my miss and excess HC's? For the record, I've already checked the EGR modulator and replaced the plugs, wires, cap, rotor, and O2 sensor with new replacements, and replaced the distributor, coil, and ignitor with used replacements. The timing is set at 5 deg.

86longbed

No ideas?

84sr5yoty

Hard to say. I had a minor lean miss that I had a hell of a time tracking down. As a final attempt, I completely bypassed the EGR valve, EGR modulator, and even the BVSV, and the miss went away. I can blow a small amount of air through my valve after a good cleaning as well, so I assume the poppet isn't completely seating from carbon build-up. Being that the poppet is deep into the valve making it impossible to scrub clean; the only possible attempt to fix the problem is to replace the entire valve itself.

86longbed

Thanks for replying! Mine isn't leaking past the poppet. It's leaking past the seal where the shaft between the diaphram and poppet passes through the valve housing. But I guess it all amounts to the same thing: air flowing where it's not supposed to. I'll have to try bypassing mine like you did and see what effect it has.

84sr5yoty

Yeah, try by-passing it and see if it runs any better.

I disconnected the vacuum hose from the throttle body to the BVSV and plugged it off with a golf tee. You'll need to remove the metal pipe that runs from the EGR valve to the upper intake plenum and plug off the orifice in the plenum. I used a wine cork in the plenum orifice and then sprayed carb cleaner around the cork while the engine was idling to confirm there were no vacuum leaks.

A word of caution when bypassing the EGR valve; the engine will be very susceptible to pinging with the EGR bypassed since the EGR lowers combustion temps when (properly) functioning. I'm going to experiment with colder spark plugs and see if I can eradicate my pinging issue.

longhungsilver

Good luck let us know if that works but i doubt it myself.. The EGR valve Substantially lowers combustion tempertures in a way that colder plugs will not.

And to the Original poster... If bypassing the EGR seems to help you then you will need a new one to pass your emissions test

86longbed

Just an update - I tried bypassing the EGR and it did seem to run better. So I bought a new valve, installed it, and found that it actually didn't help at all. The problem is worst when the engine is at normal operating temp, and I probably didn't let it warm up all the way when I had the EGR bypassed. Seeing as how I was running out of time to get it smogged, I buried my pride and took it to a shop that specializes in Toyotas. After playing around with it all day they decided it was a bad air flow sensor. I bought a rebuilt one from Napa and found that it made no difference either. So now I've spent almost $600 in the last week and I'm back to square 1. I'm very close to just trying to sell this thing as a parts-only truck!

stormin94

If nothing else works, Take it to a smog shop in a smaller town, and slip the guy in charge a $20. He'll understand, and your truck WILL pass

86longbed

If I could get the engine miss to go away when I slipped the guy the 20 I'd do it!

It went into the shop again. Rebuilt air flow meter is working fine, but they found a bad EGR modulator (passes through too much vacuum), bad O2 sensor, worn throttle body (won't idle down all the way), and non-functional cat. They also found traces of coolant in the intake and oil in the radiator, indicating a head gasket failure. That would explain the O2 sensor and cat failure, and possibly the miss itself. I know I can fix that myself (I did an in-vehicle engine rebuild 2 years ago), but I really don't feel like messing with it anymore. My intention was to sell it anyway, and because the body and interior are in rough shape it will probably be offered as a parts-only vehicle. If I repaired it, I doubt I'd be able to get out of it what I put into it.