Problems after changing spark plugs

i have a 2001 VW Jetta 1.8T. after this routine maintenance the car sputters and the check engine light starts flashing. i adjust the gap from the recommended .028 to about .04, which the old ones were at. car is running smoother now except when accelerating from idle and the engine light still flashes. what could be causing this?

The old plugs could have a larger gap than oem recommendation. Check what the plug gap is supposed to be and set it to that. I think you meant .40 but why did you not follow the recommendation of .28 if that is the recommended gap? Start there and get back to us.

The first thing to do is double check what the gap is supposed to be according to the manufacturer and set the plugs at that gap. Depending on how old your old plugs were, that .04 was probably a symptom of age and wear.

The second thing to do is make sure that you ended up with the right plugs. Especially if you bought them at a large chain store, don’t assume that the the character behind the counter knew what s/he was doing. Do some web work to (e.g. maybe at the website for the plug manufacturer) to double check the plug yourself.

The third thing to do is to check out the wires. Make sure that you hooked them all up correctly - i.e. that the #1 wire went back to the #1 plug/cylinder etc. Also make sure that the wires are correctly seated. They should “click” into place. Finally, if you didn’t install new wires with the new plugs inspect all of the wires carefully. If you were even a little careless in pulling them off you may have damaged them. Use a plug wire tool if appropriate, and always pull & twist by the boot - never by the wire itself. If you pulled on the wires themselves you likely dislodged one or more end terminals from inside of the boot. If you replaced the wires w/ the plugs, double check that they are correct when you’re checking on the plugs.

Has your VW had all the coil issues addressed? I doubt it’s miswired, it wouldn’t run at all, or would backfire, if plug wires were switched. It is possible that an old wire might have been damaged during the plug change. And I agree with Cigroller, you’re better off with the exact brand/model plug recommended by VW.

That brings up a good point that oem plugs have many times worked out better than other plugs.

From my quick research, it looks like .040 is correct gap. You need to double check. Flashing CEL can mean misfire, so check plug wires, etc, to make sure they are OK. You may need to read and then reset the codes after you check the plug gap and wires, and then see if that resolves all CEL issues. If these plug wires are 8 yrs old or so, I would go ahead and change them anyway.

.40 is just shy of 1/2 inch. That would be one heck of a gap!
,28 is over 1/4 inch.
I think you’re dropping a zero in your numbers. But hey, it’s the end of the work week, you’re allowed…

You sir are correct, thanks for the pass, (remembering .0## stamped on the feeler gauges). I wonder too about spark plug wires as posted below, and wish to caution anyone doing their own plugs to know that spark plug wires need to be handled with care, no extreme bending or pulling on the wire to get it off the plug etc.

GM had a TSB (Technical Service Bulletin) that a newly recommended spark plug, in one of their engines, had porcelain that was a little longer than spark plug sockets were deep. Spark plug porcelain was being cracked by the standard depth spark plug socket, resulting in misfire.
I am not saying that this cracking of the porcelain applies to your spark plugs; but, it wouldn’t hurt to check your spark plug to spark plug socket depth.

The car in question is a VW. GM TSBs mean nothing.

The act of removing and installing plug wires can sometimes damage them; especially if they were difficult to remove or they were yanked straight off instead of twisting them off.

Corroded plug wire terminals at the plug or the coil can also cause a problem.
You might consider pulling the codes to see if this is a general misfire or it’s cylinder specific and go from there.

I KNOW it’s a VW. And, it does have spark plugs…like some of GM’s engines. By its being a VW doesn’t negate the possibility that the porcelain(s) may be cracked. Or, is there a magical difference between the basic designs of GM engines and VW engines? If there is, let us know.

How many miles on this VW? As others have stated, I’d go with the OEM plug and gap . . . but OK brings up a good point . . . if you are dealing with original or old and stiff wires, you may well have cracked a wire or end connector and may have “fixed” it a little when re-gapping the lugs. Not hard to find, just go over the wires from point to point, and change out those plugs for OEM. Rocketman

My story may be unrelated trivia, but I once replaced the plugs in my sister’s RAV4 with the plugs that the computer at Advance Auto Parts said were appropriate, though they were a different brand from OEM.

The plugs LOOKED identical. Same thread and tip profile. However, the car immediately developed a misfire and check engine light.

Some research revealed that these were the wrong plugs for the car. I can only speculate that perhaps the resistance may have been very wrong(?)

The parts counter guy refused to believe that his computer might have the wrong plugs listed. He just pointed to his screen and repeated “No, the plugs I sold you were correct. See, it says so right here in the computer.”

Google 2001 Jetta coils. Lots of problems that sound like your description.

That GM TSB was for a SPECIFIC GM engine and a SPECFIC recommended spark plug. Yes, there are “magical” design differences between the head designs. Some have two valves per cylinder, some three, some four. Some have two spark plugs per cylinder. Some head designs are more prone to cracking. Others are more prone to warping. Some are still cast iron, others are different alloys of aluminum. The only common similarity is they hold the valves and spark plug, and contain the combustion. Proof of differences can be found in the different spark plug designs being made. Some have longer threads than others. Some use 5/8 hex head, others use 13/16 hex. And that’s before you even get to the different heat ranges and tip materials and designs.

I’ve been turning wrench for 25 years. I’ve never heard of the problem that GM TSB warns about. Can you break a spark plug when installing or removing? Hell yes, happens every now and then. But, you know it when it happens. The problem the GM TSB warns about just doesn’t happen for other spark plug designs.

My GM car came, of course, with AC spark plugs. At 109,000 miles, although the engine ran OK, I replaced the plugs with new equivalent heat range Autolite plugs according to the chart at the store which did not have AC plugs.

The engine then had an occasional miss during low speeds. I kept with it and now a few thousand miles later, the engine runs like new again. Do spark plugs have a break-in period? If you told me yes, I would believe it to be possible.

the engine light still flashes. what could be causing this?

Well you could try getting the computer checked to find out why that CEL is flashing. That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.

There’s a chance you could have a fouled plug or plugs.