shuttering at 55-70

ok - have a 1995 uick century - recently had a tire replaced on the drint driver side, new plugs and wires installed.

Now, when I get up to around 60 - it starts to shutter and shake like it is falling apart - it ONLY does it when I press on gas - if I let up, it stops.

took it to the shop, they did a compression check on the engine, everything was fine. They said is could be a fuel enjector problem - the pressurs are as follow:

#1 172 psi
#2 180psi
#3 180 psi
#4 179 pso
#5 182 psi
#6 181psi

not sure what they are supposed to run at though.

They also said that the intake manifold gasket was leaking (could this be the problem) - but they want almost $600.00 to fix that - seems a little steep.

I though of possible the fuel filter - but when it shacking and studdering - if I push the peddle to the floor - it shifts down - and takes off with no probles - thand everything goes away when i get up to around 80 - but can't drive at that speed everywhere I go!!

Any info. would be greatly appreciative.

Thanks.

This is typical of a bad coil, plug or wire, did it do it before the work was done, info missing, if so could be a start of a coil failure or possible the convertor lock up is slipping, the trans can be checked for slippage in the tcc with a full scan with a trans function scanner. Compression is ok, if coolant was fouling a new plug could be the problem

Did not do this before the plugs and wires were changes - shop says those are all OK. wil look into the coil issue though - is thier any way to test for that by any chance.

replaced the fules filter - and no change at all. Am wondering at this point, if it could e something like a miswired plug - anyone know what the fireing order is - and more importantly - what the cylendar numbering is?

Also - the shop did mention that I may have a leaking manifold gasket - what are the symptoms of that - and could that e the prolem here?

Thanks.

I have also pulled off each plug wire - and started the car - and got a nice good spark from each wire - so all the wires are working - could be a ad plug - ut hate to take them out - it took me 3 hours to get the in

It could be a bad plug. It could be a bad wire, or a failing coil. Since this apparently didn't manifest itself until after the spark plug change, there's a strong possibility it is related to the plugs/wires. Excessive plug gap can cause that. Weak spark from a damaged wire can cause that. Incorrect wire placement can also cause that, but would likely cause shudder at lower RPM, and at idle, and any loading, not just at 50 MPH+.

Just a few more pieces of information would help:

Firing order - Which engine? 191 V6? 207? 231?

What spark plugs did you install (brand and part no.)?

What was the plug gap after you set them?

That is what I have been thikning - somthing with the plugs./wires - ut have not found anything wrong with anything - pulled out all the plg - double checked the gap at .06 (what is printed on the car label, and what is listed in the book at wal-mart) - don't remember what the pug numers were - but the ONLY ones listed in the wal-art bok for that car - so did not have many choices thier. Shop we took it also checked, and everything looked fine.

Engine is a V-6 - 1994 uick Century
plug gap - .06

Coult his be a major vacume leak - caused by the manifold gasket leak?:banghead:

Am wondering at this point, if it could e something like a miswired plug - anyone know what the fireing order is - and more importantly - what the cylendar numbering is?

The '94 or '95 Buick Century was delivered with the 3.1L, Vin "M" since it is a V6. On one post you state you have a '95 model and on another '94?

Regardless, for the 3.1L:

Firing order is: 1-2-3-4-5-6

coil pack Left to right 5-2 3-6 4-1

rear bank left to right 1-3-5
front bank left to right 2-4-6

It would be nice to know what brand spark plugs and ignition wires you used?

ok - the plugs are autolite 6245 and the wires are the NAPA Belden Max 700790

Checked everything - found #3 and #5 were switched - got the fixed, car runs a it better, but still has the shake, and studdering.

ok - the plugs are autolite 6245 and the wires are the NAPA Belden Max 700790

Checked everything - found #3 and #5 were switched - got the fixed, car runs a it better, but still has the shake, and studdering.
Pull the plugs out tjat were switched and look at them, may be fouled, also that engine thrives on the proper AC delco plugs and " premium" wires the Autolites wll not hold up.

hmm - OK - well, will get some new plug at napa tomorrow - the best they have and see what happens - they wires are supposed to be better then what the car came with - so will go with new plugs to start - will let you know what happens with that

recently had a tire replaced on the drint driver side, new plugs and wires installed.

get the tire balanced. I had the same problem and it wound up being that my front tire/s were unbalanced.

Nothing against WalMart (O.K., actually, I have a LOT against WalMart), but trusting an in-store advertisement, salesperson, or label on a box that claims the wires are BETTER than original is very risky. For general purpose use, there is probably no better secondary ignition wire than the Packard wires which were originally installed on the vehicle.

That aside, I'd have to second maxwedge's suggestion to use original equipment quality, dual platinum plugs of the proper heat range. If you get the AC/Delco plugs, you won't even have to think about it. If you use Champion, NGK, or someone else's plugs, you may have to do some investigation to make sure they are correct. Just because they physically fit the head doesn't mean they are correct for the engine.

And to clarify bnaylor's post, the firing order is indeed 1-2-3-4-5-6, however, the description of the cylinder arrangement may have been confusing. Conventional terminology dictates that the LEFT side is the driver's side of the vehicle, regardless of what particular part or item you may be describing. Therefore, by that understanding the rear cylinders (which is also called the RIGHT side of the engine) are numbered 1-3-5 from right to left, and the front cylinders (also called the LEFT cylinder head) are numbered 2-4-6 from right to left. Asa you stand at the front of the vehicle and look at the engine, that would be from YOUR left to YOUR right, so you have to make that mental reversal. The same applies for every component on the vehicle.

By those same conventions, the coil pack is numbered as follows:

http://72.19.213.157/files/191CoilPackOrder.jpg

And to clarify bnaylor's post, the firing order is indeed 1-2-3-4-5-6, however, the description of the cylinder arrangement may have been confusing. Conventional terminology dictates that the LEFT side is the driver's side of the vehicle, regardless of what particular part or item you may be describing. Therefore, by that understanding the rear cylinders (which is also called the RIGHT side of the engine) are numbered 1-3-5 from right to left, and the front cylinders (also called the LEFT cylinder head) are numbered 2-4-6 from right to left. Asa you stand at the front of the vehicle and look at the engine, that would be from YOUR left to YOUR right, so you have to make that mental reversal. The same applies for every component on the vehicle.

There is nothing to clarify or confusing from my post. What I described is looking in from the front of the engine. Pretty simple and not too confusing to me. :biggrin:

Evidently the user was able to find a crossed ignition wire.

Unless the coils have been replaced or moved around the numbering is normally clearly visible.