Jump to content

engine problem on 88


KDirk

Recommended Posts

It looks like my long stretch of uneventful ownership is taking a sudden hit. First the problem with the rear wheel on my 91 'vert, now a new problem with my one 88 coupe. Yesterday, quite suddenly, I found that acceleration was very poor above 20 mph, and the engine struggled to get up and go, wanting to run high RPMs and kept shuddering/missing/surging. Also made a "screaming" noise under heavy acceleration. Did some poking around and discovered a huge air leak from the EGR valve blowing towards the firewall. Pulled and replaced EGR valve, and at first things seemed ok - no more hot air blasting out of EGR valve into engine bay, and with engine cool, it seemed to have it's pep back.

Then I got on the highway for a test drive. Still had poor acceleration, really struggled to get over 50. And still a noise, not as bad as prior to replacement of the EGR but very noticeable on heavy application of accelerator. Wants to get into the 3300+ RPM range to get any speed going over 15-20 MPH, as if it is stuck in 1st or 2nd. And of course is running abnormally hot under load.

So, I suspect I may have another air leak, but so far have not located the culprit. I have checked much of the vacuum lines, no problems found there so far. Exhaust apparently not restricted (can feel normal exhaust at tail pipe at idle and under acceleration with car stationary). PVC valve and grommets intact, and no readily apparent leakage from the intake manifold, as there is nothing dripping out onto the ground.

I should note also that the "squealing" noise is apparent while giving it heavy pedal even in park, so it is not the transmission. Engine otherwise sounds normal (no strange mechanical noises as if something internally is damaged/broken). Temperature stays normal as long as I am driving <15mph and light on the pedal so don't think this is an exhaust or valve issue.

I am heading back outside now to do more troubleshooting, but wondered if anyone might have a brilliant suggestion to make in aiding my search.

KDirk

Link to comment
Share on other sites

Looks like I'll be checking the cat today. Pulled EGR valve again last night including the mounting adapter and installed new gaskets still the same symptoms. Can't figure out why the cat would fail spontaneously though. Car has under 50,000 miles and has run great until now.

Will check back in after some more troubleshooting.

KDirk

Link to comment
Share on other sites

It does sound like a plugged catconverter. The squeaking you hear may be due to back pressure causing the exhaust manifolds to leak.

Here is another possibility: The garage where I once worked had an older Cadillac with similar symptoms. The problem turned out to be the Cadillac had a pipe that ran from the exhaust manifold to the catconverter that had dual walls to make the exhaust quieter. The inside wall of the pipe had collapsed due to corrosion causing the exhaust flow to be blocked. That would account for the symptoms starting suddenly. I have no idea if Buick used the dual wall exhaust pipes but it is worth considering.

Link to comment
Share on other sites

Interesting Ronnie, I had (owned) a '74 Cadillac hearse awhile back, and it had that double walled exhaust pipe, only mine had the inner wall collapse in the pipe behind the muffler. I cut that section of collapsed pipe out for show and tell. The outer shell was perfect. The tipoff was a wheezing sound out the back.

Link to comment
Share on other sites

Guest Corvanti

i had the same problem several years back with a '88 Beretta GT. i also replaced the EGR and the problem went away for a day or two - but i didn't drive far (a couple of miles) then the problem came back and it was the cat.

the "easy" for me would to take her to a locally owned muffler shop and check the exhaust flow. cats are much less expensive now if needing replacement.

i "know" a guy that cut his cat off and used a 14" long drill bit to remove part of the interior of the cat, and replaced it on "his" car. problem solved. but this was in a state that didn't "smog check" that year vehicle in inspections - just that the cat had to be on there. i was advised that it ran better than ever!

so..... :)

Link to comment
Share on other sites

Well, didn't get this done today as I decided to fix the 'verts rear wheel problem. Put on new driver side hub/bearing and rear brakes. Now it spins true and has no rear brake rattle. Just finished a test drive to verify and it's all good.

Will deal with the 88 problem this week yet. Will disconnect the exhaust and check inside of cat. If it is collapsed or plugged I will actually be relieved as I am drawing a blank on what else could be wrong at this point.

I feel a little better that I have one back to being road worthy. Stilll concerned aboutthe 88 until I have a firm answer on what's wrong. A bad cat would be the simple, easy fix. I hope it isn't something more serious.

KDirk

Link to comment
Share on other sites

Back in the mid-70s, my moms '73 Electra also had the collapsing inner wall exhaust problem. Happened during a rain storm going through a large puddle.

You can measure the exhaust back pressure via an adapter screwed into the O2 sensor hole.

Link to comment
Share on other sites

Well, the cat is out of the bag, so to speak. Cut the converter out this evening. Visually it looked perfect inside from either end. Gave it a shake, however, and it sounded like a box of rocks.

Out came the hand sledge and the buster bar. Broke all the catalyst out until inside of housing was completely clear. Banded unit back in temporarily and went for a test drive.

Boom! Problem is not only fixed but the persistent annoying stumble on shift under acceleration between 55 & 60 is completely gone. Hertetofore, I had assumed the latter problem was a vacuum leak or transmission I had never been able to pin down. Well, consider it pinned clear out of existence now. Looks like I may see a marked improvement in fuel economy as well. Will know in a few days.

The thing I can't understand is why it failed. Current mileage is 49, 2xx so it's not like this car has had a hard service life prior to my ownership. In retrospect, the cat must have been partially obstructed since I first bought the car as it clearly explains the stumble under acceleration at highway speed. Never would have expected the cat until this recent incident made the car run so poorly.

In any case it is fixed and life is good.

KDirk

Link to comment
Share on other sites

Ronnie,

Hard to say for sure. Subjectively, I think it is slightly louder at the tailpipe, but not obnoxiously so. I suspect I have a very small leak at one of the stainless bands holding the cat to the pipe as I sometimes hear a whine, almost a faint "whistle" on acceleration now. Probably exhaust pressure sneaking around the clamp. Will need to do a more permanent fix involving some welding as th clamps are strictly temporary.

KDirk

Link to comment
Share on other sites

Guest Mc_Reatta

Thanks for the info. Sounds like cat gut may be a topic of interest on other than the tennis forums. :rolleyes:

Link to comment
Share on other sites

Just for information purposes: I flow tested the stock cat. vs stock gutted vs a modern replacement vs a straight 2.25" pipe. All tested @ 28" wc or about one psi. Stock cat flowed 272cfm, gutted 323cfm, Walker universal cat. 355cfm and a straight 2.25" pipe 425cfm. I suspect there is a fair amount of turbulence inside the empty housing to account for the significant difference but still a good useful increase. The straight pipe flows the best but would certainly fail a visual test.

Link to comment
Share on other sites

2seater-

Well now that is useful to know. I'm thinking a mod to slide a 2.25" 308 stainsles straight pipe right through the center of the cat housing is the best of all fixes. That way it looks stock but benefits from max air flow improvement. A little cutting, a little welding and voila.

No emissions check in MO for anything older than 1996 (obd2) so no worries. Will pass safety on visual "check" for presence of cat. Most aftermarket cats are junk, which is why they have very little scrap value versus factory converters. They also seem to have short life spans before they clog or collapse. I'm not blowing money to put that garbage on my car.

KDirk

Edited by KDirk (see edit history)
Link to comment
Share on other sites

Guest Corvanti

Kevin, i think that's why my "friend" drilled out a few holes in the cat instead of dumping all of it out - to keep the flow fairly straight. your solution is better than his!:cool:

Ronnie, i think it would be hard to tell the difference in loudness between a "good" cat and one that was cleaned out a bit. it should be a little bit louder than a clogged one - but since my "friend" had a C3 Corvette, he didn't care.

remember that even if your State laws don't have smog checks, the Federal laws do not allow "tampering" with cats or other smog equipment.:rolleyes:

Link to comment
Share on other sites

I think I'll pass on that. Have enough things on my plate now. And, just when I thought I had this behind me, it popped an E064 EGR code on the way home tonight. Looks like more troubleshooting tomorrow. Marvelous.

KDirk

Link to comment
Share on other sites

Just a thought but could the increased back pressure from the clogged cat have caused the EGR to blow out ? Could be a weak point.

Back in the daze of the first cats (mid '70s GM), they had a screw in plug on the bottom and was easy to just dump out the beads. By '78 they started sealing the plug.

Link to comment
Share on other sites

2seater-

Well now that is useful to know. I'm thinking a mod to slide a 2.25" 308 stainsles straight pipe right through the center of the cat housing is the best of all fixes. That way it looks stock but benefits from max air flow improvement. A little cutting, a little welding and voila.

No emissions check in MO for anything older than 1996 (obd2) so no worries. Will pass safety on visual "check" for presence of cat. Most aftermarket cats are junk, which is why they have very little scrap value versus factory converters. They also seem to have short life spans before they clog or collapse. I'm not blowing money to put that garbage on my car.

KDirk

That is the best solution if you have the ability to modify. Your own conscience on the pollution question. My experience has been a slightly more guttural idle sound and a more pronounced V6 buzz on acceleration but not objectionable to me. Have you done the rear manifold modification? That tends to deepen the tone slightly. I found my old data on flowing just the rear manifold using the front manifold crossover as the inlet. All other exhaust ports closed off. Stock flow 241.5cfm and 326.8cfm ported. From observations of several rear manifolds, there is quite a variance in the quality of that inner opening, some better than others. I use a hole saw that just fits inside the pipe so I can cut the inner part of the O2 bung off as well. Not needed as the O2 seals with a gasket on the outside.

Link to comment
Share on other sites

  • 2 weeks later...
Guest Dan Gibbs

Hey All :)

I've read and heard years ago that removing the cat reduces "necessary back-pressure" from the motor and can cause issues. Is this really true with an engineering-basis or is this just a bunch of "tree-hugger hokum" passed down to mechanics from the "emission-Al-Gore's" upon high?

From what I remember at the time, they said that an engine needs a certain amount of back pressure to run properly, but I can't remember why it would be any different than say a '66 327 or '73 350 which never had cat's to begin with...

Is it a lowering or raising of the motor's vacuum overall from stock spec?

Link to comment
Share on other sites

It's mostly hoken, at least in the case of our Reattas. The exhaust isn't really tuned in any real sense and the camshaft has almost zero overlap. If the concern is about pressure available to ensure EGR flow, the available vacuum in the inlet manifold far outweighs the exhaust backpressure. I have measured the normal backpressure in most operating modes. I installed a pressure tap in the rear exhaust manifold next to the O2 sensor. At low speed and highway cruise, when the EGR would be operational, the exhaust backpressure is <1psi . My engine vacuum shows about 12"Hg at highway cruise of 70mph. The approximate relationship is 2"Hg vacuum equals 1psi so in this example, the intake manifold vacuum is pulling approximately six times harder than the exhaust would be pushing.

As to the question of raising or lowering operating vacuum, I cannot say for sure. I have operated two different engines in this car, one ported and with higher compression and the other bone stock, also turbocharged in two different configurations and as well as normally aspirated. Vacuum readings are essentially the same in cruise conditions. Those old mile-o-meters are just a vacuum gauge and if you have ever connected a manifold vacuum gauge and watch is as you drive, they are extremely sensitive to your right foot. Generally higher vacuum with smaller throttle opening, which should indicate better mileage, but it increases actual pumping losses for the engine. EGR does two things. It cools the combustion process due to the introduction of inert material, (good for emissions), and also requires greater throttle opening to maintain power, reducing pumping losses and actually helping fuel mileage.

Link to comment
Share on other sites

I have no empirical data to add to that, but will say the car runs just fine with no cat. In fact, it runs slightly better without it in terms of acceleration when compared to my other 88 which still has the functional cat.

Having said that, I will likely put a cat back on as I have found the exhaust noise level inside the car at highway speeds to be a bit more than l care for. Will probably get a Walker as my previous experience with aftermarket converters has been very poor.

KDirk

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...