Source of High Speed Ping

[nograin]

I've got some part-throttle ping once the Wag is warmed up AND moving.

I have pretty much solved it by running 94 octane Sunoco. But, that shouldn't be needed on a vehicle designed for 87 octane.

Here is my theory, what do you guys think?
Since there is no problem at Wide Open Throttle, or when cold, the problem is either in the EGR or in the distributor vac advance signal. That is, either the distributor is either getting full manifold vac when it was supposed to switch to ported, or the EGR isn't getting its signal (valve does work).
If the CTOs failed, I would think they would fail the other way around. So, bottom line is that I think its the non-linear valve is a little flakey after drinking gasoline, or the egr passages are partially plugged, so at higher speeds it doesn't get as much exhaust gas as needed to quench the combustion.

Matt


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360 727auto-trany, NP229
body by beer (PO) :(
carries wood inside
no "wood" outside
My other car is a fish

[David Simon]

Matt,
I think a partially blocked EGR is a good possibility. My 88 GW was doing the same thing before I took it apart to rebuild the top end. When I pulled the intake the exhaust passages for the EGR were about half blocked with carbon. I've cleaned it and replaced the valve but I'm not done putting everything back together yet. I think I'll be done this weekend and I'll let you know if the pinging stops.
David


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98 Cherokee (wife's)
97 TJ with all the goodies
88 GW
TFI Upgrade

[nograin]

Thanks David,
Let me know how it goes.
I finally found some info on the non linear valve under ignition in the TSM. After staring at it for awhile, it doesn't seem like that would be the cause, but I could be wrong.

[David Simon]

I'm getting closer. I got the heads, lifters, push-rods and rockers on after work today. That non-linear valve is an odd looking thing, there doesn't seem anyway to test it. Hopefully the ping will be gone when I get mine running again. Let me know if you find something out before then.

[millerlo]

I was having the pinging problem as you noted and spent some $s solving it. I went through the system to make sure all the vacuum line were correct and installed all new ones (make sure no debris is present in the new ones- it happens) changed the dual CTO, plus all of the others, made sure all of the delays and check valves were right, changed the radiator, distributor, put on a rebuilt Carb.,EGR, rebuilt air pump, TVS, truck spark plugs and silicone wires, pro coil, Flomaster Delta muffler, adjusted carb,timing, and then passed the clean air test. Ran really great, but still had the high speed ping which got louder as the temperature increased. Read about removing the EGR vacuum delay, put in a straight connection and no more spark knock,ping and problem. I sware I also gained 50 horses at the same time. Now it acts like a 360.

I do think that all of the rest of the improvements and changes made for a better vehicle, I had an '81 Limited and'82 Limited which I'm using for parts (still runs) and this is an '89 Grand. Mike Miller

[David Simon]

Wow, talk about taking the long way home, at least you got some good benefits from it. Before I started rebuilding the top end I replaced all the vacuum lines, did the TFI upgrade, rebuilt the carb, installed new plugs, cap, rotor and wires.
Thanks allot for the info. If it still pings when I get it back together that's the first thing I'll try.
David

[nograin]

Now I'm going to go look at that again. I think I so that in one of the IS Bulletins, but will have to check if there even is such a thing on the '85.

Coming back this evening the engine got flakey again on me, dies when I accelerate too quick. Its only 4 blocks, so hard to evaluate, but its happened before. The vac lines are all new except the little tiny ones, I think the CTOs are hanging up occassionally from disuse and drinking gasoline. This is maybe off topic because it never pings when I just drive around "town".

When I used it Wednesday on a real trip it was fine. But thats basically on 94 octane gas. This new tank is 93 octane and we'll see how it does. MPG is quite decent now, averaging 14 mpg on the country roads, about 10 in the city.

[nograin]

OK. It looks from the TSM/IS stuff that the 85 did not have a check valve. Looks like the 360 vac diagrams are the same for 85, 86, and 87, but I'm not positive. Guessing 88 is different.

I did find a service bulletin for the 86 that suggests Ting the powervalve source from the rear vacuum port (going to the vac resevoir) if you have surging. Thats instead of the normal T into the front manifold port going to the CTOs etc. Why it doesn't also apply to 85 I can't figure... anyway thats not our problem.

[Bandit]

Had the same problem. If your motor has been rebuilt, and you didn't use a good quality head gasket, the compression could be a little high. Re-did the head with a good quality thick head gasket and runs like a top now on mid-grade and will run on reg.