Buick 3.8 poor performance

kellyjeff19

New Member
Joined
Jul 7, 2019
Hey guys iv been digging thru forums looking for some one that has had the same problem is as me but haven’t had any luck finding anything. So I have a rebuilt 3.8 na even fire it’s been bored .60 over turned crank new cam all new bearings timing chain Quadrajet carb new rebuilt new hei distributer wires plugs and this engine will not turn more then 3000rpm and it seems to be hitting a wall also it only gets 10mpg. i have tried multiple carbs based on my results I don’t think it’s fuel system related this engine is in a 1979 Toyota pickup and is adapted to a 700r4 I don’t have a lot of experience with these 3.8s so I’m not sure what to expect anyone got any ideas?


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15 degrees at idle with vacuum advanced unplugged I have advanced and retarded it it didn’t seem to gain any rpm i was thinking maybe a bad ignition coil


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What springs did you use in the heads? How does it idle? Any reason to think the cam got wiped. What oil used?
 
Lucus 5/30 break in oil no metal in the oil new oil pump/timing cover the engine runs and idles good I can drive it 70mph just won’t go over 3000rpms it doesn’t back fire or anything just hits a wall at 3000 and won’t go past it around town it does pretty good but trying to get into passing gear is a problem heads are stock heads I lapped the valves and reran the factory springs new with new intake seals i don’t have any reason to believe I have a flat cam


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Check spring pressure. How many miles were on the heads? Have hit a wall do to spring pressure before just not usually at 3000 rpm but then agin I have never ran a NA 3.8.
 
Yeah unfortunately I didn’t get to drive it before the rebuild but I did rev it before the rebuild and it reved clean to red line with poor oil pressure I’m sure spring pressure could be a factor but I’m thinking it could actually be a bad hei distributer if I still had my old one I would throw it back in just to see but I threw it away I’ll order another distributor and swap it in just to see how it responds my problem definitely feels almost timing related does anyone know what the total timing should be on this 3.8na


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Sounds to me it is a valve spring problem. What does it have for valve lash adjustment ?
 
As others suggested, seems like a valve spring issue.
 
Yeah unfortunately I didn’t get to drive it before the rebuild but I did rev it before the rebuild and it reved clean to red line with poor oil pressure I’m sure spring pressure could be a factor but I’m thinking it could actually be a bad hei distributer if I still had my old one I would throw it back in just to see but I threw it away I’ll order another distributor and swap it in just to see how it responds my problem definitely feels almost timing related does anyone know what the total timing should be on this 3.8na


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Total timing should be 34 degrees with the vacuum advance disconnected. The advance mechanism in these HEI distributors get gummed up sometimes. See if you can move the rotor to see if it will advance. The power valve in the Q jet may be stuck also. Another problem these NA engines had was loose or frayed wires on the distributor pick up coil. When you stepped on the gas the vacuum advance retarded and the wires would loose the connection or short out. Your swap is similar to mine. Hope you find the problem.
 
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Yeah I think valve spring pressure is not my problem as far as I can tell I am not floating the valves at 3000rpm almost everything is new that’s bolted to the engine I did run a compression test on the engine 120psi on all 6 cylinders wasn’t the 150psi I was hoping for on a new rebuilt motor but that’s well within firing range on most engines I will dig into the distributor tomorrow and check and see if I can find any ignition problems


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I've diagnosed a few vehicles with a similar running condition.
The problem was a restricted/clogged exhaust.
An easy test is to disconnect the head pipe from the manifolds and take it for a test drive.
 
Exhaust is true duals 2.25 mufflers are strait thru glass packs no cats exhaust flows well and is only a month old


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What are you using to read engine RPM?
I had same issue once reading RPM from a Autometer tach that was in v8 mode, I had to cut one of the wire loops in the back of the tach then it displayed RPM correctly. Just a thought
 
Factory Toyota cluster that was a thought that I had to I’m going to buy a digital tac timing light and recheck everything it still seems under powered I don’t think my tac is off very much


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Did you check push rod length after you machined everything ? It is extremely important with a shaft non-adjustable type rocker assembly.

if you have a push rod that is to long it will hold the valve open all the time.

I will be more than happy to help, you if you want it.
 
Did you check push rod length after you machined everything ? It is extremely important with a shaft non-adjustable type rocker assembly.

if you have a push rod that is to long it will hold the valve open all the time.

I will be more than happy to help, you if you want it.


Now there's a real offer!
 
Well I never milled the heads or block and my compression readings are 120psi on all 6 cylinders correct me if I’m wrong but doesn’t that rule out push rod geometry I gues they could be to loose but I haven’t bounced one off the rocker arms yet lol


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You did not even get the surfaces even cleaned up ?

What thickness head gasket you use ?

If your push rods are to long when the engine is running 6K or so RPMs, the oil pressure is at it's highest so your lifters are pumped all the way and not allowing the valve to close all the way while the lifter is on the cam base circle.


Pull the coil plug off so the engine will not start.
Pull the rockers off, clean the valve tips well, use a black sharpie marker to paint them all. Install the rockers and turn the engine over only a few times.
Pull the rockers off again to see where the wear marks are.
 
The surfaces got scraped clean and a light wire brushing on the iron heads and block factory gaskets in my engine tech gasket kit were used I will have a new distributor tomorrow morning I will give that a shot before I dig into the valve covers but here’s the cam specs
Valve Lift (INT/EXH): .450"/.474"
ADV Duration (INT/EXH): 280°/290°
Duration @ .050" (INT/EXH): 204°/214°
Centerline: 112°
Power Range: 1,000-4,500 RPM


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