Van was running great! Then, this past Monday I was driving home from work (engine had been running about 5 minutes) and it hesitated badly while accelerating. When I stopped at the next red light, it was idling bad/rough. Then, the check engine light came on.

I went to Autozone and had the code read. It was P0402, which indicated excessive EGR flow at idle. Over the past couple of nights, I've tried numerous things, but I can't seem to locate the source of the problem. I have the Ford diagnostic CD (gotta love eBay) to help me, so I have done all of the diagnostic routines for P0402 to no avail.

Symptoms:

Rough idle
Engine shakes at lower RPMs - seems to disappear at higher RPMs
Miss/shudder while at cruise speeds with light throttle, no symptoms during hard accel
Exhaust note seems to sound different - puffing noise

What I've done:

EGR system: I realize excessive EGR flow could cause my symptoms due to a leaning of the mixture. First, I disconnected the vacuum line to the EGR valve to make sure the EGR valve was not being opened unintentionally - no difference. Then, I took the EGR valve off completely and blocked the intake orifice - no difference at idle. However, it seems like the miss/shudder may have improved during cruise. DPFE sensor was replaced - no difference.
Vacuum system: all hoses are intact and connected, sprayed down intake manifold area with carb cleaner - no idle change detected, so intake manifold gaskets seem okay.
Ignition system: plugs (Bosch) and wires (Bosch premium) are new (< 1 year), moved wires - no response, checked boots - all boots firmly connected
Fuel system: fuel filter was changed less than 1 year ago, added injector cleaner - seemed to make slight difference, possible clogged injector?
Sensors: no other codes present, cleaned MAF - no difference, tested IAC (< 1 year old) - works fine, tested TPS - works fine

What I still might try:

Compression: puffing=bad valve?, test cylinder compression
Fuel system: test fuel pressure to make sure within spec
Ignition system: check wires for resistance, voltage check to ensure coil(s)not going bad. Ignition problem seems unlikely since miss does not occur under load.

Please help!

 

If you are certain the problem is not in the vacuum system, then the next step would be cleaning and/or replacing the Idle Air Control (IAC) valve. Often just cleaning with a few blasts of carb cleaner will restore function, other times it is too badly gummed up and replacement is required. If cleaning does not greatly improve performance, check the vacuum line to the fuel pressue regulator for evidence of fuel at the connection point. If the line is wet, the regulator is bad.

There are other more draconian possibilities but it is best to start with the most commonly encountered and least expensive routes.

 

Hey AeroC.....

Where exactly is the IAC? Might be a good idea to check mine if I knew where the Da*n thing was...!

What happened to your Avs!!!! (Insert evil laugh here)

-reever

 

"then the next step would be cleaning and/or replacing the Idle Air Control (IAC) valve. "

aero, the IAC is less than a year old. Plus, I tested it to see if it was working by disconnecting it. The RPMs dropped when I disconnect it.

"check the vacuum line to the fuel pressue regulator for evidence of fuel at the connection point. If the line is wet, the regulator is bad."

I cannot see/access where the vacuum line attaches to the FPR, but I did remove the vacuum tree at the back of the intake manifold that supplys the vaccum to the FPR. No evidence of gas. With the vacuum tree port plugged, the idle was the same. Also, if the FPR is bad, wouldn't black smoke be present from the tailpipe? I'm going to check the actual fuel pressure tonight via the Schrader valve on the injector manifold. This should confirm if the FPR is suspect or not.

Other important points, I forgot to mention:

99k miles on it
Checked PCV valve operation too. Removed PCV valve and plugged vacuum line - no change in idle. Cleaned and reinstalled PCV valve - same idle as before.

 

Well, I had a similar situation, but without the EGR code (my '95 doesn't an EGR). The problem with my van was a bad exhaust valve seat. The symptoms were very similar to what you are experiencing and the puffing in the exhaust is a pretty good (or in this case, bad) clue.

If you are still stuck after running all of your EGR diagnostics, run a compression test, or better yet, do a leak down test. Don't believe the manual when it says that more than a 25% deviation indicates a problem. In my case, it was around 20% for cylinder with the bad seat. There was another cylinder with a bad exhaust seat, exept it only measured 10 psi lower than the others. However, it wouldn't have lasted long.

 

Problem solved!

Before I went out and bought a fuel pressure gauge, I decided to pull the spark plugs. Although they were less than a year old, I thought I might as well rule them out. As most of you are aware, it's not the easiest thing to do on the 4.0 L.

Plugs are Bosch double platinum. Center electrode is small and located on end of ceramic post approx 1" long.

1, 2, 3: were all a very nice light tan color. electrodes were in tact. so far so so good!

4: whoa, 3/4" of the center electrode was gone! essentially, there was no electrode.

5: not as nice as 1, 2, or 3. electrode appeared pitted.

6: same as 5

Since so much of 4 was missing, I was praying that it didn't damage the piston or the valve/valve seat. I did stick a magnet tool into the #4 cylinder but nothing was retrieved, so it must have gotten smashed to pieces and spit out or chipped off slowly over time. Anyway, I went to Autozone and got three new matching plugs. I put them in and she runs smooth as silk now! Why 4's condition generated P0402, I am at a loss.

FYI: I noticed the owner's manual lists two types of plugs depending on what cylinder is invovled. The ones for 4, 5, 6 have different suffix that means they are double platinum. The others are single platinum. I'm thinking the design of the engine is such that 4, 5, 6 are exposed to more pressure, heat, etc. If 4, goes to crap again, the Bosch plugs are history. OEM Motorcraft plugs will be what I replace them with.

Thanks for all your replies!

 

Clarification:

Researched Bosch plugs and Ford's EDIS ignition. Apparently they are incompatible over time since EDIS is a dual polarity system. Dual polarity systems fire both from electrode to ground in one cylinder and from ground to electrode in another. This also explains why all the plugs on one side of the engine were fine, while the other side's (4, 5, 6) were all crappy. That must also be why Ford requires double platinum plugs (platinum electrode and platinum ground) anytime a plug is replaced. As stated in the Aerostar owner's manual, when you replace plugs, they must be double platinum. This must be because most people would not know which cylinders would work okay with single platinum and which cylinders would require double platinum.

Apparently, Bosch is now aware of the problem. They should make consumer's aware too. I never would have bought them, had I known about this long-term incompatability ahead of time. As it is, now I know they are going to fail again. When one does, it's time for Motorcraft double platinum.

 

I would like to find a good Ford diagnostic cd. Can you let me know which one you bought? Thanks, Jim

 

i know this is from eleven years ago but i have the same problem and traced it to no compression on cylinder number one.

 

I'll never understand why a person would use any spark plugs other than the ones specified by the vehicle manufacturer.

 

use the Autolite AP103 plugs, not the APP103. I already contacted Autolite about the ceramic insulator cracking in the APP103 plugs in my 1997 4.0. They know about it but will tell you that "noone else has complained about it".

 

How timely. My van just started to idle roughly on initial start up, like at least one of the cylinders is not firing. But after a minute or so, it runs normally. I was thinking that maybe I have an injector leak. But would one of these cracked insulators behave the same way? Or would they just run crappy forever?

I'll have to pull them out this weekend to check.

 

Had your symptoms and it turned out to be a plug. The ceramic around the center electrode was split in half lengthwise. Still hanging there inside the plug. It amazes me why it ran okay after it warmed up.

 

yes, I bet it is one of the plugs, and the chances of it showing up in codes as a "misfire on cylinder X" is 50/50. Sometimes it just does not show up in codes.

the failed plug(s) start by missing intermittently, has to do with temperature I suppose, then it gets to a point where the missing is constant and the engine starts to run on 5 cylinders.

Last time it happened to me I started chasing one spark plug after another, replacing one at a time, and of course it turned out to be the last spark plug I removed, the most difficult to get to, had the cracked ceramic insulator, which I sent to Autolite and they sent me replacement plugs.

 

first time I hear of this, the factory label under the hood of my 1997 4.0 states AP103 and nothing else.