Quick simple question

[jsawyer1181]

Ill keep this simple lol. I did a tune up on my car and it had 3 fouled plugs in it. I replaced the cap, wires, rotor, plugs, and pcv valve. I didn't go with name brand or anything but I gapped the plugs around 0.50 as it said on the sticker. The sticker said the gap should be 0.48-0.52 so I just put it in the center. I used Autolite plugs and Autozone cap, wires, and rotor. The reason I ask is because once the car is warmed up and lets say im sitting at a light, I get a bit of what feels like a minor misfire. Its kinda rythmatic so im not sure if its just cuz its a older car or whatnot. Doesn't really bother me as like I said its minor. It doesn't affect the performance of the engine unless the engine is cold. Even then its very minor. Feels like it has a miss when its cold and u give it light throttle. Once it warms up its fine, but it has a slight shake. Any ideas? Its minor so im sure its a simple fix. Thanks guys.

[91waggin]

Hard to know where to tell you to look unless we get some more specifics about the car. Welcome to the forums BTW, I see you're new.
Usually what we do around here is put the specifics of our cars (year, type, engine, mods, miles) in our signatures (see the user control panel) so that we don't have to remind people of them all the time.

Regardless, I need you to clarify a little bit, because your post was a little bit confusing. At one point it seemed like you said it happened when it's cold, another point you said it seemed like it happened when it was hot. Could you restate the problem please?

Some general information you should know about the 302 engine that comes in most of the cars on this forum:

Because of the firing order chosen for the "lopo" 302s, they tend to beat up the main bearings. As the engine ages, this becomes noticeable as a lack of oil pressure at hot idle, and, as the problem gets worse, you will start to hear a bearing knock.

The reason I'm mentioning this is because (I think) you said the problem happens at hot idle, which is when the "lopo knock of death" becomes most apparent. If it really is happening at hot idle, put an oil pressure gauge on there to see if it is low oil pressure.

[jsawyer1181]

Oh its a 1991 Grand Marquis 302 Lopo with around 160k on the engine. It doesnt have a single knock or rattle to the engine at cold or hot idle, it just feels like a very slight miss. I'm thinking it might be a fuel filter? It feels like it could also be ignition related but im not sure. The engine sounds really good and doesnt have any hesitation on acceleration. Ya I know about the main bearing issue with the 302 but it hasn't made any noises that would suggest that. I will however check it just to be sure.

[91waggin]

Does the miss happen when the engine's cold or hot, or does it matter?

Change the fuel filter. For the price of a fuel filter, it's always worth it.

Also, disconnect and plug the vacuum line going to the EGR. The EGR valves on these cars misbehave often. If the miss goes away when you disconnect the EGR, than it was your problem, and you should probably make sure that it's not fouled up with carbon and gunk, and that the EGR position sensor isn't fucked up.

[jsawyer1181]

Oh and it has no mods whatsoever. Forgot to mention that. I'm not too worried about the misfire much as it is very slight. What I mean by very is you have to be really looking for it. So I'm thinking its going to be something minor. I just wondered if it was because I used discount parts maybe? Or the plug gap wasnt right or something. Its so minor and doesnt seem to make a difference on the way the car drives so I don't think its really a major issue. So what I'm wondering is would using cheaper cap, rotor, and wires would make it have a slight misfire? Or do the plugs have to be gapped at exactly 0.52? Thanks

[cld783]

what kind of plugs? platinum or copper? autolites should be pregapped at .50 and anywhere between .48-52 is fine. either you got a bad batch of chinese plugs or you messed up on the gap.

did you have this problem before the tuneup? maybe the plugs fouled out for a reason.

[FatNasty]

Any plug wires or boots getting burned on the exhaust manifolds anywhere?

[jsawyer1181]

I'm thinking that it might need a fuel filter because who knows when it was changed last. The car ran like crap when I got it and the plugs hadnt been changed in a VERY long time. I have just ur basic autolite plugs in there right now. I gapped them at 0.50. I will check the egr valve as well becuse that could very well be the issue. It does it worse when its cold, but becomes less when its warmed up it is however still there. Sometimes its worse then other times. When I changed the wires I made sure they werent going to be touching the manifolds but I will check them again. Example when its cold and I start driving sometimes I get that kick back from a misfire. When its warm I don't get it at all. It still has the occasional misfire though. When its warm and im sitting at a light, it has a occasional misfire that isnt very bad, but its there. I'm just really picky I know lol. Like if im sitting at a light you can really feel it, kinda like a little bit of a shake. I did however verify it is a misfire as I can hear it out of the exhaust. Ill check a few things like the EGR stuff, any ideas?

[Lincolnmania]

were those autolite plugs made in china?
i had really bad luck with the made in china autolite plugs......it appears that they are made in mexico now.....maybe you got some old stock?

[jsawyer1181]

I'm not sure if they were or not. I got them maybe a month ago. I'm actually thinking about putting motorcraft plugs in just to see. I have no idea how the car really ran before I did the tuneup because when I got it the thing had 3 fouled plugs from sitting for over 8 months with really old plugs in it (also were autolite plugs). How can I check to see if they were made in china?

[91waggin]

on the package

[jsawyer1181]

Lol I don't even have the package anymore. I will check a few things to see what could be causing the misfire like the egr valve. Thanks.