STILL chasing an odd misfire issue (I think?)

Maintenance/Repairs
1

So I have a '99 ford escort 2.0 SOHC engine that I just rebuilt the head on (pre-valve seat drop). When I did that I also changed the timing belt, serpentine belt, thermostat, cleaned the intake manifold, have new spark plugs, wires, radiator fluid, transmission fluid, PCV valve, and IAC valve. I also replaced a couple of vacuum tubes that were bad. HOWEVER, I’m still having a odd issue with this car!

I figure I’ve got some sort of sensor or fuel related issue, but here’s a brief description of what I’ve noticed. The car starts and runs with throttle just fine. Sounds good, everything seems ok (except for the thermostat which isn’t seated properly causing the car to run basically cold, but it will be fixed within a day), but when at idle I get random misses or ‘catches’? Basically once the car has been running for a few minutes and i stop at a light that I have to wait for, the car will idle fine, then slow a tad (barely noticeable), ‘catch/lurch/miss?’ and then run fine again briefly and repeat. The frequency of this is not consistent and it happens at random, but increases with engine load. If I have the headlights on and the A/C (defrost) on it happens more often, but again, always during idle only. When sitting parked, in park and the headlights off, it almost never does it.

Anyone have any suggestions? I will attempt to run a fuel pressure test tonight to see if there is anything on that end, I have no check engine light or codes currently so i’m kinda at a loss. Should I try to reinstall my old IAC valve? Does this sound like some sort of other ‘common’ symptom? Injectors? It’s frustrating tracking this thing down, but again, any input/tips you could give me would be useful.

2

A small vacuum leak will do this.

The EGR system can do it as well. You can test this by temporarily disconnecting the vacuum line. Plug it with a golf tee & cap the port on the valve with a vacuum cap or something like it.

A power issue can do it as well - marginal alternator, marginal ground connections for high draw accessories (e.g. cooling system fan).

3

I know this is a stupid question, but where is the EGR system/valve located? The chilton book doesn’t describe it very well, and says it is non existent on several engines. Is it the round tank that the heat pickup tube goes to off of the exhaust system (located on the intake manifold)? if so, would I be plugging the top of the EGR valve, or the vacuum line I take out of it, or both?

4

It sounds like you have it right. It looks like a little flying saucer stuffed down behind the throttle body. Its on top of a metal tube that goes up front, under the ignition coil & all of that & attaches with two bolts to the exhaust manifold. There’s a vacuum line that goes into the top of it - probably with an elbow on it. The size of that is about exactly right for a golf tee. You want to plug that, and cap the port that it plugs onto on the valve.

My '97 currently does something like what you describe. Its intermittent. I can make it go away anytime I want by doing this.

Of course, odds are also good that you may have overlooked somethings else - a small vacuum line, a bit of a leak left in the intake manifold, a dirty ground…

With that thermostat not quite acting right you are probably also running too rich.

Did you follow the exact torque procedure for the head? They’re stretch bolts & tightening them down correctly is a 3-stage process if I remember correctly.

5

Thanks for the continued support cigroller. That’s what I thought the EGR was. I didn’t actually clean it out when I had everything taken apart, so maybe I’ll take it off and give it a quick cleaning if I can easily access it. I’ll give the plugging a try today when i re-seat the thermostat. I’m pretty sure I’ve got all the cabling and tubing right but I’ll double check that as well (again). There is one tube that slips onto a metal box attached to the body on the firewall that isn’t dry or cracked, but it does have some cuts in it right on the end where it slips onto the metal box that did seem a little ‘iffy’ to me yesterday when i was doing the final hookup. I did indeed tighten the head bolts in the proper sequence as well as tightened them in a three stage process. I’m going to recheck the torque on them tonight just to be sure.

6

You can’t really recheck the torque on the head bolts because the last stage doesn’t go by an actual torque spec. Its just a final 90 degree turn if I recall correctly. I actually scored the top of mine so I’d know if they ever backed off.

I would find out if the EGR is involved before pulling it. Its not that hard to pull, but still might be needless. If it is involved, then cleaning out the EGR might help. When you turn it over to where it attaches to the pipe and peer inside, what you see in there is about a dime sized plunger. If you give it a good shove it will open up. It opens up when vacuum is applied, but if it is gooked up, it could be sticking open sometimes at idle. But its also kept closed by a spring which might just be getting weak.

7

well unfortunately i didn’t get your message till this morning since I couldn’t access the car talk community all of yesterday afternoon. I did end up pulling and cleaning out the EGR valve yesterday evening when I swapped out/fixed the thermostat.

After cleaning the EGR the problem still persists. what happens is the car tries to enter a really low idle and that’s where stuff starts happening. After cleaning out the EGR last night and starting the car up we noticed that the car seems to hesitate for a second coming out of idle, as if it’s not getting fuel or something, but once it is out of idle it runs fine/great. Didn’t get a chance to check the fuel pressure last night so I’m not sure if that could be an issue or not.

Last night I did get a pending code of misfire in cylinder two, but when I rechecked after I got to work it had disappeared. Is there any chance that back when my problems started spark plug in cylinder four got slightly fouled (didn’t look like it was when put them back in), and now that spark plug is sitting in cylinder two? It was suggested that I swap the spark plug on cylinders 2 and 3 to see if the problem moves with the plug, but again, any other suggestions/input is welcome as well. Also, I’m really thinking of putting my OEM “bad” (though now I doubt if it really was bad) IAC controller back on to see if that does make a different.

8

Ok, so this car is really starting to drive me crazy! I absolutely love it, but it is punishing me without any giving me any sort of information. So I want to say I have an EGR system issue, but I can’t tell for sure. Here is what the car is currently doing:

When cold the car runs just fine, idles ok and has normal throttle response from what I can tell. Once the car is warmed up however all hell starts breaking lose and the car’s behavior is erratic. It has been increasing in it’s severity and today got bad enough for me to post back on here. Basically once the car is warm and I step on the throttle sometimes I get a good throttle response/power, other times I get very low power and some shuddering. If I take my foot off the gas for a second or two and reapply sometimes the power comes back full strength and sometimes not, but until recently it had always gotten back to normal eventually. On the highway the car seems fine when at speed. In stop and go traffic however, the car really acts erratic, and I even had a couple of misfires or backfires as I heard some loud pops/clunks followed by the flashing check engine light which goes away after about 15 seconds and the car sometimes smooths back out, and sometimes not.

I recently replaced spark plug #2 as I had gotten some misfire issue with that cylinder, but since then it has been ok. The head is recently rebuilt so I can’t imagine it is a valve seat. I thought maybe the EGR valve was getting stuck open, but by a simple test of sucking on the input of it and releasing I can hear the valve open and pop closed just fine. Is there still a possibility I could have an issue with the EGR system? Any other ideas on what this could be? if you need more specifics/details on how/when this happens let me know, I pretty much have it nailed down on what causes it (hot engine/under the hood, but in normal temp range according to the dash). I really ideally only need this car to last till Wednesday the 14th, or maybe even this weekend, but I’m still curious as to what this could be. I have a OBD II cable to USB, so if you also know any good free diagnostics software besides what came with the cable let me know and I could also get information that way. Thanks again!

9

Is a #2 misfire all you have for codes? Specify - all codes & exact codes.

Your software is probably OBDWiz. Unless you’re an expert there’s not another software that will do better at diagnosis. Computers can’t diagnose. They can only give data to people - who still have to diagnose.

The fact that the EGR opens up is irrelevant. A clogged or stuck closed valve will set codes, but it won’t make the car run rough at idle. This can come from a valve that opens when it isn’t supposed to. I told you all the way back in the first post to temporarily disconnect it. Pull the vacuum line and plug it with a golf tee or similar. Cap the valve with something. It will set a code.

You need to check the compression before you do much else.

10

Computers can’t diagnose. They can only give data to people - who still have to diagnose.

Sure they can…They just need all the data. You should see the systems we use to diagnose some of our telecom systems…thousands of more complicated then all the components of any car made…Their diagnosis is 100% accurate 99.999% of the time.

11

We’re talking about cars and OBDII systems Mike.

12

OBD-II you’re right. I thought you were talking about computers in general.

But there is work on the new OBD systems that will drastically increase the computers ability to diagnose problems…The problem is that the number of sensors on a car will increase by a factor of 10. Just more things that can fail if you ask me.

13

Right, I guess the statement seemed to be a blanket.

I’m with you on not increasing the complexity - especially if any of it is geared toward making the computer “knowledge” better. The “smarter” our machines get the “dumber” we all get and the crazier the world becomes. Not with everything, mind you. But the direction of things tends to be guided by “because we can…” rather than “is this really a good idea…?”

14

To the OP: try a bottle of Techron in the gas tank.

15

I’ve been meaning to do your golf tee trick cigroller, I just haven’t been to the store to get one, and don’t really have other items around the apartment of appropriate size. You are also right in the fact that the software is OBDWiz. I was just hoping for software that could access previous info/code information on the computer. Currently it is giving me nothing, but under similar circumstances from before when I took my car in they were able to tell that cylinder 4 had misfired over 17k times even though there was no code at the time. That’s the type of info I was hoping to see, not just a current code.

Speaking of codes, when I got to work this morning I finally got a pending code from the car via my handheld code reader. Yet another P0302 aka misfire on cylinder 2. This is indeed the same code I got before (though before it did propagate to a full P0302, not just a pending). I was just doing some light searching, and I know with cars the same symptoms can equal a thousand different diagnosis, but is there a chance it could be a clogged fuel injector? This is what I just read from a site which pretty much seems like it explains what is happening:

“if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions. Lean misfires can cause newer systems (OBDII) to read a misfire code or multiple codes depending on the effected injector(s).”

Or do you think it is something with a sticking valve as you had mentioned? I know you say I need to do a compression test, but I can’t do any of that till this weekend, so really I’m looking for ideas to hit with this weekend when I’m able to get to it.

I’m not saying it is since I have no idea, but would a clogged/dirty fuel injector let the car run fine when cold, but not so good once it is warmed up? ie once the fuel leans out to normal operating temp mix? I mention this because to remedy this issue in the past I first tried running some STP fuel cleaner through, and that actually made it seem really good for awhile, then a tank or two after using the cleaner it started having issues with idling. I eventually got the P0302, so I thought maybe it was a fouled spark plug from before. I changed that out, the problem seemed good for a little while, and now it is resurfacing again. All in the same cylinder. I’ll try running another bottle of cleaner through the system to see if it helps or not.

I should also mention (probably much to all your dismay) that when I was cleaning out the intake port a month back when getting ready to re-install the head that some of the black gunk/carb cleaner mix did flow back onto the injector heads/surfaces as I was cleaning. I tried cleaning the heads off with some more carb cleaner and Q-tips, but who knows if any of it got lodged in there?

I’m still puzzled by why it seems/feels like it idles fine (especially when cold), but under certain accelerations conditions it just goes to hell.

16

In addition to checking the compression, swap the #2 injector with another one. See if that code/pending code moves with the injector.

The ignition coil pack on these cars are also often a problem.

You can stuff anything in the vacuum line for the EGR - the stakes are practically nil. Ball up a piece of tissue if nothing else. Except that with the seemingly consistent indication of a 2nd cylinder issue, I’d be leaning away from that. (But it is a 30 second operation so nothing lost).

17

Forget the STP. Get some Techron. Try it double strength.

18

Thanks again for the inputs. Since I can’t do anything mechanically till Saturday/Sunday I’ll try circuitsmith’s idea of the double strength techron today first and see if it helps improve anything over the course of the next two days. This weekend I’ll possibly swap the injectors if I get no improvement to see if I can pinpoint that as an issue.

Most frustrating part about this is that I just need it to survive a week since that is when I get my new car! It however has started making me wonder if it will or not :s

19

Oh yeah, just to make sure I get the right stuff, am I getting the fuel cleaner, or the fuel injector cleaner? I’d assume the injector cleaner obvious, but just making sure. Would it even matter?

20

I don’t think it matters much, but I would get the injector cleaner.