It happens warm or cold. I forgot to mention that I swapped in a 02 sensor a few days ago. Holy crap that was an ordeal. On top of everything else, I need to get it smogged to renew my tabs. I bought the sensor, I went to the mechanic for the smog, the same guy also smogs (from the verb “to smog“). He loaned me his Snap-on 22 mm to put it in on the street. Using both arms I could barely get the damn thing to move for about 3/4ths of the extraction. Putting the new one in only slightly easier. Somehow I emerged relatively unscathed. He told me that he’s seen them so badly seized that he had to cut the nipple out and weld in a new socket.

I had read that a bad O2 sensor would lead to hesitation issues. The new one had no effect, but I’m pretty sure the old one was aging out anyway. I am wondering about vacuum issues as well.

When I first saw the symptoms 2 to 3 weeks ago, I limped into an O’Reillys and put in plugs, cap and rotor, cables, and air filter in the parking lot. I always have a set of tools with me. The old plugs looked pretty bad, and it ran 90% better. It’s been a strange experience, hopefully I’ll get some valuable lessons from it.

I haven’t had the new plugs out for a looksee yet, I’m thinking to take one or two out later today.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

He did ask about warm cold ...

About the IM gasket The 5L gm's of that era had a corrosion issue with the gasket. I think the Olds 307 was the worst. I think they were aluminum? And that manifested in a coolant leak into the valley and cylinders. any coolant loss? IIRC the corrosion/leaks were usually at the rear on the driver side of the motor.

Is the engine light on? Pulled any codes?

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Satan creates nothing: he only ruins everything. He does not invent: he tampers. And his followers are no different ~ Archbishop Carlo Maria Vigaṇ

Well, yes he did ask about it and I answered. The problem is about equally bad warm or cold.

Funny you should mention, there has been a persistent coolant issue that I cannot solve. I put in a new radiator a few years back, my mechanic found a couple of freeze plugs that were in bad shape and leaking, and yet there is still a slow leak. It never goes terminal, but I have to top the damn thing off. I have wondered a few times if I’m a nut job for keeping this running.

The only intake manifold gasket I’ve changed in my storied career was on one of my BMW E30 325i units. That was a tricky job, but it did the trick. It was going into loping at low rpm, I would be herky-jerking around turns.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

The only code in all of this has been 43, knock sensor error. I checked it out, the line was pulled off, I put it back on, still got the code. I have a new sensor, I didn’t have the right socket to take it out. Will be a PITA to get out. No indication of knocking.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

The tbi of that era was notorious for losing one of the two injectors randomly resulting in four of the cylinders (dual plane intake) starving for fuel and skipping. If you watch the injectors while it is idling you will see a difference in spray patterns. The injector that is not spraying a conical fan spray has failed.

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Satan creates nothing: he only ruins everything. He does not invent: he tampers. And his followers are no different ~ Archbishop Carlo Maria Vigaṇ

That sounds a lot like what’s happening. Doesn’t seem like one cylinder missing, all of a sudden it cuts out quite a bit. If you floor it, will falter a bit and suddenly surge. High end performance is still pretty good which leads me to think that the engine is in relatively good shape in terms of compression.

I checked the MPG, I’m only getting about 10 now, normally it’s 13 to 14.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

There was kind of clue. When new spark plugs indicated a substantial improvement.

Strength and color of ignition spark. It should look healthy. New plugs may have done better on a weaker or erratic spark than the old ones did.

I thought a lot of these gm engines where subject to marginal pick up coils in the distributor?

Very easy job. Unbolt the IM and bolt it back on with the new IM valley pan gasket after cleaning up the corrosion, and use plenty of appropriate sealants. It was so common that it is amazing your example lasted so long without having that done. I knew a guy that recommended it as preventative maintenance to his customers. and they all loved him. I was first alerted to this when I witnessed him doing one and asked about it. I took my 307 apart and was astonished at the corrosion about to be a problem and thwarted it in the bud. namaste

Well ;

If you like it, I'd think it well worth the $ .

The valve seals will smoke on decel and when you first start it, I'd do a compression test followed by a leak down test before thinking about pulling the heads......

I can dig not wanting to do it your ownself ~ *IF* you have an honest and COMPETENT Mechanic let him have at it but in the proper order please :

Compression test followed (if necessary) by a leak down test, if that's okay then have him do the intake manifold gasket , the valve stem oil seals can be done with the heads in place if he's competent .

If there's low compression or a leak down problem, time to sit back and think how much $ you want to drop in .

To me, every vehicle is a tool and I use them hard so I don't mind putting $ into repairs .

For us old armchair Geezers who know how to do it, this is a fantastic thread .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Great! Glad you like it.

OK, raise your hand if you thought the hesitation problem was a CAT that was disintegrating internally. I needed to get it smogged now anyway and I just barely passed HC two years ago so I figured a new CAT was in the works. After he told me I consulted the Google and sure enough, there are opinions that say such a CAT will lead to hesitation and surging, which is exactly what I had.

He said the new cat was an improvement but still not perfect. He had to put in a T connection with nipple on the fuel line in order to test the pressure. He said it was only at about 6 or 7 and it needs to be 13. New fuel pump. Runs ideally now.

While the tank was out he looked it over for crud, said it looked pretty good. Took out a few bits of something.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

Yay, it's done for now .

These little weird problems are why no one wants to work on older vehicles ~ it takes a day or two to exceed the vehicle's dollar value .

On the other hand, I love sorting out weird problems as they are teaching moments .

My neighbor had a really clean 1971 Chevy 1/2 ton G - van he'd bought new, the sliding side door was rattling badly and hard to close, I told him if he didn't fix it soon it'd fall off, and sure enough ! .

I asked him if he wanted to fix it and he said no, I'll get $800 scrap value for it.....

Sad IMO as it ran *perfectly* and didn't require smog testing, the cloth interior was still pretty good .

Most of the time I'm like the old Studebaker guys : I'd rather fix than switch

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I looked at the spray patterns when I had the air filter out, I didn’t notice your part about “at idle,” but when I revved it slightly the patterns looked good, the same on each side. I’m guessing would be good to look more closely at idle - problems might reveal themselves more obviously at idle as opposed to higher RPM.

At any rate, gory hallelujah, my van feels like new. I asked my mechanic Ky, pronounced “key”, if he thought I should get the heads done, as he agreed that the smoking could be a valve guides issue, he said no, just run it.

I’m thinking that I would be happy to get trouble free usage of it for numerous months before spending large again, this whole episode cost me about $2000 - Ky was $1600, I probably spent about $300 on parts myself - I’m happy to cut the cash spigot off for now on this one.

For that $1600, parts and labor, I got CAT welded in, fuel pump installed plus tricky fuel pressure test enabled, front suspension lubed, and knock sensor installed.

As for the cloud of smoke at start up, I feel a bit guilty about it, not sure how bad that is on the air pollution index. I am sure however that getting the heads redone would be a major, major event in terms of time and money. I’d rather wait a few more years and get a new engine. I’ve read numerous times that the mpg on the 5.7 is almost as good as on the 5.0. It makes sense, because you’re still moving the same tonnage around. Seems that extra gas usage would mainly happen on hard acceleration.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

I’ll bet he could sell it to someone for that much or more. Plenty of guys are into the “no smog” issue. My welder neighbor long had a ‘74 IIRC pick up that he was restoring. Had a small V-8, he said it was the holy grail of pick ups.

As for exceeding the value of the vehicle, I think keeping this running and cherrying up the body will not be a net loss. I get so many offers for this thing. Well, not cash amount offers but “do you want to sell it?“

And it’s always a question for me, how much would it cost me to get something else that is as useful? No way I’m going to buy a vehicle this good for $2000. But then I said the same thing about 16 months ago when I paid Ky $2000 to rebuild the tranny. It had lost all except low and reverse. I would sometimes drive it around at 15 or 20 miles an hour, 25 an hour when people were pressing me. This for a few months until it was rebuilt. It runs perfectly now. I’m pretty impressed, rebuilding an automatic tranny is like rocket science for me.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

Good deal. A 5.7 is not more efficient as the architecture is the same. More displacement takes more fuel to do the same motions as the 5. I would get the valve guide seals changed as they the smoke is robbing power and hurting your new cat.

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Satan creates nothing: he only ruins everything. He does not invent: he tampers. And his followers are no different ~ Archbishop Carlo Maria Vigaṇ