Looking at D150 terrible spark knock

-

michformulaS

Well-Known Member
Joined
May 14, 2005
Messages
818
Reaction score
44
Location
Midland Michigan
I am looking for a D100 or D150 long bed truck as a personal work truck. I looked at a 1984 D150 tonight that has no rust (rare here) 318 motor was rebuilt 10,000 miles ago and 15 years ago. He said flat tops and built by a shop with receipts to be 9:1. He also said the heads were decked and valves were enlarged to 2.02's. When I drove it and gave it about 1/2 throttle not letting it kick down it had very bad detonation. It was not hot and it is cool out here tonight. He said Oh Yah it has always done that I forgot to mention that I just don't give it that amount of throttle I either back of or let it kick down. I decided to pull the vacuum advance just to see if it made a difference. It didn't. I am thinking it is running lean.He added an Edelbrock 600 cfm carb at the time of the rebuild. Truck doesn't smoke and had good oil pressure so I am leaning to take a chance on it. Looking for opinions.
 
Could be timing, also seen a 318 where the little EGR nipple screwed into the intake under the carb fell out, it acted just like you describe
 
He said he had played with the timing and better gas in the past and it acted the same. Hard to diagnose with a 10 minute test drive and his recollection of what he tried.
 
Could be timing, also seen a 318 where the little EGR nipple screwed into the intake under the carb fell out, it acted just like you describe
I assume the EGR nipple would have caused a lean condition because of vacuum leak? I am sick. I want to buy this truck just to mess with it and see if I can fix it!
 
I'm not sure what it caused, just that it acted just like that...I'd buy it, swap a $300 magnum 5.2 in it and drive the wheels off of it!
 
Spark knock is relatively easy to diagnose and fix once you have the time. I wouldn't let it keep me from buying the truck.
 
I'm not sure what it caused, just that it acted just like that...I'd buy it, swap a $300 magnum 5.2 in it and drive the wheels off of it!
I have a decent LA 318 sitting on an engine stand right now. I just don't want another project. I really don't want to spend more than a Saturday afternoon on it.
 
Definitely leaning towards buying it. A good price will help me justify any work I need to do. Just to disclose everything he is asking $3000 for an 84 D150 with nice body and interior. One solid color on American Racing 15" turbine style wheels. Everything works but the radio. I am thinking offer of $2200 to offset my Saturday afternoon. That'll pay for the time and beverages.
 
Consider that if it has been knocking for a long time there could be engine damage.

I was just up in your part of the world. My wife and I were on Mackinac Island, and drove down I-75 coming home. Beautiful up there.

Good luck with the truck.
 
I think 84 still had the lean burn ignition in it.
2 plug.
Just wire in a single plug electronic distributor and it should clear up.
 
Check the intake for the presence of a working EGR valve. If you disable it, then there is no way for the Exhaust to enter the intake, even with the floor-jets removed.
To prove the EGR valve is closing. Just stick your fingers underneath diaphragm, at idle, and lift the diaphragm up. The engine should stall or nearly so. If it makes no difference then the circuit is not working, unless the engine is already idling like crap, then the valve may be stuck open, which I have only ever seen once,lol.

I have an 84 here, and only a few years ago it was a great truck.
Try and get a compression test done before you buy it.... if the pressure is over 165psi, getting rid of the detonation could get expensive.
Buy it for the body, and do whatever it it takes to get rid of the detonation.
 
-
Back
Top