Old Slant 6, Bad Ping

[Winston]

I have a friend with an old '84 Dodge D150 pickup with the good 'ol slant 6 engine. Recently, it failed smog. So, he threw some money at it. Had tha carb rebuilt, new catalytic converter. And it still failed. He then determined that the spark control computer was not working correctly because the vac advance diaphragm had a hole in it. So he got a new computer, installed it, and the car started pinging like crazy. So, he readjusted the timing and it still pings. He tried to retard the timing bit by bit, but it still pinged. Eventually it was retarded so much that it affected the idle speed but it still pinged. He tried a tank of premium and it still pinged.

The truck has 175k miles on it, and it has not been maintained real well. Probably sludged up and full of carbon. Still it is strange that it pings so much.

He is going to try a can of seafoam through the PCV valve. He is also going to do a cooling system flush. Any other ideas?

 

[kingrob]

If the pinging is not computer related and its actually the engine, the simple fix on these old slants is 20w50 and some octane booster plus premium gas. If that doesn't work I'd just wait till (insert favorite engine destruction scenario here) then try a rebuild if you really want that engine to run good.

 

[Winston]

So, pinging is common on these engines? With the old computer he did not get pinging, but he also got no timing advance. The engine was very gutless.

Solution is premium gas with octane booster. Seems expensive in the long haul due to the poor mpg of this vehicle.

 

[ediamiam]

my old '82 toyota used to ping somewhat until a mechanic cleared out the egr, I think.

 

[Jon]

If it ran for a long time with no advance it's probably carboned up real bad. Do a carbon clean on it using Seafoam or Marvel Mystery Oil (or run a mega dose of MMO for a tank). Give that a shot.

 

[Winston]

I thought about the EGR, but from the exterior you can see that the valve modulates fine when he revs it up. Plus, the NOx values are very low, and from what I understand, the NOx values would be high if the EGR was plugged.

I think it is just carboned up too. He drives it around town a lot. He is going to try the Seafoam through the PCV hose.

 

[TheTanSedan]

Seafoam is nasty stuff.

A MolaSoak is a much better proposition. LUBE CONTROL isn't harsh in the manner of Seafoam, and literally eats and digests the carbon, safely. Not just breaking it up.

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=5;t=000169

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=5;t=000226#000003

And here's an old thread near identical to yours:
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=5;t=000600

Be sure to change the oil afterwards. I like to do an LC soak overnight on an annual basis; it has kept me from having to change fuel octane on four vehicles, some 1970's, some 2001. I haven't used NEUTRA as yet.

Follow this with an ARX run.

Also check the distributor shaft for wear.

 

[The_Jeff]

allpar.com has some good slant 6 tuning info. Sounds like under the old comptuer he wasn't getting any advance over base b/c the computer was seeing WOT from no vacuum. So if there were carbon buildup it was masked by the retarded timing.

Apparantly a good fix is to ditch the computer and put in an early 70's distributor with ordinary vacuum advance and an appropriate carb. This might be tough to get away with considering CA's smog laws. Anyway try to dig up some articles from old guys who've seen this 20 years ago.

 

[andyd]

This maybe apples and oranges but....... My old Jeep 360 v-8, actually has a vacuum retard running off a ported vacuum source controlled by coolant temp. The distributor has centrifical advance. This is a Ford distributor BTW. Any thing messed it up and they ping like crazy. Even a crack in the vacuum line . This was Detroits way of dealing with emissions back then. Cheesy, low budget add on parts to 60s engines, instead of higher tech fuel injection/ engine management. That is why early 80s cars are practically all gone. Most of them never ran right from the start. Rants over, I would try the Seafoam, I hope it works. I had some success with it.

 

[Winston]

Yes, he replaced the vac advance. On this partuclar engine the Vac advance diaphragm and the spark control computer are mounted together. Then that whole assembly is attached to the air filter housing. That whole computer and vac diaphragm assembly was changed out with a rebuild unit. I will tell him to look for an adjustment screw inside the diaphragm, but I am doubtfull that there is one.

I am pretty convinced at this point that it is just an old engine that is all carboned up. Maybe he will try the Seafoam this weekend. We shall see what happens.

 

[CBR.worm]

Now that he has passed emissions he could always put the old diaghram/computer back on to test. It may be pinging because of a lean mixture, maybe he could change to cooler plugs.

 

[Mickey_M]

quote:

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Winston:

... So he got a new computer, installed it, and the car started pinging like crazy. So, he readjusted the timing and it still pings. He tried to retard the timing bit by bit, but it still pinged. Eventually it was retarded so much that it affected the idle speed but it still pinged. He tried a tank of premium and it still pinged. .... Any other ideas?

---

You might look for a vacuum leak.


.

 

[Winston]

He has not passed emissions yet.

We did look for a vacuum leak. Sprayed WD-40 all around the intake manifold gasket and the carb to intake manifold connection.

 

[kcryan]

ITALIAN TUNE UP!!!!!
id do that, with either a "Gary Allen", a mega FP does, or techron.

Also seafoma and mabye a piston soak sound good.

 

[TheLoneRanger]

quote:

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He then determined that the spark control computer was not working correctly because the vac advance diaphragm had a hole in it.

---

Winston, did he replace the faulty vac advance? If so, the new one may have a too sensitive calibration. Many vacuum advance cannisters have an adjustment screw, accessed through the vacuum port. A 1/8" allen wrench will adjust it.

If the Dodge's v.a. is indeed adjustable, have him turn the screw in a couple turns, then test drive. This will decrease the sensitivity of the v.a., reduce the timing advance when accelerating, and stop the pinging.