Buick running issue problem opinions

Engine is a 1970 SF code 455 Miles unknown. A constant medium miss and rough idle still prosist in the engine. Things that have been checked.

Tuned up , wires, plugs, Cap, button ,Swaped plugs and pulled several times. Is hitting on all cylinders tried different point settings timing and mutiple inspection.

New rebuilt carb and flush fuel system, Swaped carbs, checked for vacuum leaks along intake , carb ect.

removed valve covers and check rocker arms and cam movement ( engine is very clean) Didn't see any issues. Took reading with dial indicator

Removed spark plug wires while engine was running all are hitting but # 3 and 5 are a bit week effect is mininal but noticable.

Ran compression check on all cylinders Cyl # 2,4,6,8,1,7 are all 150lb cranking compression Cyl # 3,5 are 138lb did this numerous times. Removed plugs in both cylinders performed compression test again. same readings. So no blown gasket between the two.

Checked for water and head gasket issues and dont see any.

My gut is telling me possible cracked seats or burnt valves. However just doesn't make since being compression not below 90 in those cylinders and remain fairly high. Thought about retaining a borescopes and seeing if I could see anything.

Like to have opionions form you 455 gurus out there. Just putting it out there before ripping this thing down.

 

Re: Buick running issue problem opionions

Check to see if there is play in the distrubitor shaft (woble).

 

Re: Buick running issue problem opionions

Distribitor is new....thanks keep them coming.

 

Re: Buick running issue problem opionions

did you check your fuelpump? A weak fuelpump will starve the engine of gas in the higher RPM range,and cause it to sputter.

 

Re: Buick running issue problem opionions

Fuel pump is new and car misses at idle as well. Thanks keep.
It coming.

 

Re: Buick running issue problem opionions

chased a vacum leak for weeks thru 2 carbs, 2 distributors and 2 manifolds before i found it, use starting fluid spray it near the manifold head seals and the carb basr looking for a change in the idle

 

Re: Buick running issue problem opionions

That has already been done already as well. No leaks.

 

Re: Buick running issue problem opionions

when you pulled each plug wire, did it seem to make the same difference for each cylinder?

Paul

 

Re: Buick running issue problem opionions

Paul, he said he pulled them all, one at a time, and 3 and 5 did not make a big difference. He also said they were a few pounds lower on compression than the rest. Brandon

 

Re: Buick running issue problem opionions

Thanks Brandon

At this point I would do a leak-down test to see where the leakage is on 3 and 5.

Paul

 

Re: Buick running issue problem opionions

Leak-down test didn't really reveal any issues. Mulitple test a couple percent loss.

 

Re: Buick running issue problem opionions

Try a different coil,the one your using may have an internal short.

 

Re: Buick running issue problem opionions

Good idea on the coil. Cheap cost for a new one and should be replaced anyway
Keep them coming.

 

Re: Buick running issue problem opionions

I was more interested in where the air leakage was going rather than the actual percent of loss.

As you mentioned, there is a strong possibility of cracks in the cylinder heads.

It looks like the problem is common to both #3 and #5.

Paul

 

Re: Buick running issue problem opionions

I didn't hear anything when doing it. I will perform the test again in the next day or too.





UOTE=pmuller9;2129534]I was more interested in where the air leakage was going rather than the actual percent of loss.

As you mentioned, there is a strong possibility of cracks in the cylinder heads.

It looks like the problem is common to both #3 and #5.

Paul[/QUOTE]

 

Re: Buick running issue problem opionions

What about a cupped lifter on those two cylinders? I think you are going to have to pull it apart to find it.

Nelson

 

Re: Buick running issue problem opionions

but I know with MS weak battery voltage will cause constant miss weak battery voltage will cause constant miss and the car to run very poorly just my o2 good luck

 

Re: Buick running issue problem opionions

It sounds like you are doing everything thoroughly. You didn't say how long this miss has been going on or if it just appeared out of nowhere. The only thing I have to question is your leakdown quote of "only a few percent". You don't know the mileage and I'll assume you don't know how it was built. From my experience unless an engine has some Total Seal rings in it you will usually get more than a couple % especially as the miles rack up. If it is an original engine 20% wouldn't be out of hand as long as it is not just one cylinder high and the rest low.

I like to use a stethescope to listen around when doing it. I'd be listening to #3 cylinder while pumping up #5 to really make sure nothing is leaking across. One trick I like to do is to take the cam/rockers out of the equation by removing the rockers when doing the leakdown test. You can then do the test at TDC and BDC to look for something suspecious.

The compresion test is too transient to notice a difference between #3 plug in while doing a compression test of #5 or vise-versa. They should all be out when doing it anyway.

I've been noticing heavy wear in valve seats causing bad sealing in non hardened seats in the last few years in only 10000 miles. I think it really has a lot to do with the alcohol in the gas because I never really noticed the problem before with the regular unleaded that had been available just 5-6 years ago. The leakdown should pick up on that though.

I also had a broken 2nd ring land that caused some off idle miss that was worse around 1700 rpm and then got better as the rpm went up. The bad valve seats did about the same.

One problem going way back was a bent rod caused by water getting in a cylinder and hydraulicing it. I broke the starter on that one among other things. I didn't realise the rod had bent and put up with a slight miss until I could track it down. When I finally did a compression test that cylinder was low because the piston was sitting way down in the clyinder. Piked up something like 3 tenths after I fixed it.

I installed a '70 455 in one of my cars that I got somewhere allegedly rebuilt (rings and bearings, std. bore with factory pistons) at one time and it was cheap enough. I wondered why it had the slightest off idle miss to it. Very subtle as it revved up a little. Otherwise it ran pretty good. For whatever reason I had the heads off doing stuff and I noticed that one of the pistons had been replaced with a'71 and up model causing that cylinder to be lower compression. Live and learn.

 

Re: Buick running issue problem opionions

I checked that side of the engine with a dial indicator and recorded the average height and none seems out of spec. However I do believe you are correct about having to tear the engine down. Just want to exclude all possibilities first. ou:

QUOTE=Redmanf1;2129571]What about a cupped lifter on those two cylinders? I think you are going to have to pull it apart to find it.

Nelson


[/QUOTE]

---------- Post added at 08:41 AM ---------- Previous post was at 08:34 AM ----------

I bought the car this way. I assume the car has never been rebuilt . I plan on doing the leakdown test again and paying more attention this time. When stating A couple % I meant average loss for a engine. This car sat for a long time before I bought it so who knows if this is why it was parked.
Anyway I just thought I would put out a think tank on the issue before a teardown. You made some very good points. My gut is telling me a head issue. Though I just dont understand
why it is missing with that kind of compression.
.

 

Re: Buick running issue problem opionions

I checked all cylinders again . I hooked a air hose up to each spark plug hole and pumped 120lb air. No major leakage,very little if any at al
Checking again each spark plug seems to be hitting. Gonna try a new coil when I get chance. 99% sure heads and rings good. Possible
Timing chain issue. Coil doesn't
cut it front timing cover is coming apart.






UOTE=kingdaddycreel;2129760]I checked that side of the engine with a dial indicator and recorded the average height and none seems out of spec. However I do believe you are correct about having to tear the engine down. Just want to exclude all possibilities first. ou:

QUOTE=Redmanf1;2129571]What about a cupped lifter on those two cylinders? I think you are going to have to pull it apart to find it.

Nelson


[/QUOTE]

---------- Post added at 08:41 AM ---------- Previous post was at 08:34 AM ----------

I bought the car this way. I assume the car has never been rebuilt . I plan on doing the leakdown test again and paying more attention this time. When stating A couple % I meant average loss for a engine. This car sat for a long time before I bought it so who knows if this is why it was parked.
Anyway I just thought I would put out a think tank on the issue before a teardown. You made some very good points. My gut is telling me a head issue. Though I just dont understand
why it is missing with that kind of compression.
.[/QUOTE]