To be clearer about my question....
Short answer:
After several repairs the car has been running rough (see long explanation below).
Last week while out-and-about I decided to stop the car, leave it running, pop the hood, and try the “unplug the MAF” maneuver that had been described in several forum posts.
The second I unplugged the MAF, the car died. Plugged it back in, and the car started. I haven’t tried this again to verify it always dies. Therein my question.
For those interested in hearing the history behind the repairs I made, which may have caused this issue….read on……
Long answer:
(history behind what is turning into a CF) – [You’re one patient person to read through all this!]
• I have a 93 ATX.
• Was having continual CE issues and throwing KOEO codes that pointed to DPFE/EGR problems. Both had been replaced recently, so I had the Ford Dealership look into it. They said the PCM needed to be replaced. I have a hard time believing that (since outside of the CE codes, it ran fine). I didn’t think those hardly ever failed, and since new replacements aren’t available, thought I'd do some research here on the SHOForum – before ordering a used one from SHO Source.
• Found enough evidence to suspect that the cheapo DPFE from Autozone might be bad (as others had experienced here).
• At the same time the KOER threw TPS and MAF codes.
• So…..bought the new Motorcraft replacement for the DPFE (with new plug adapter). And being the ****-retentive, OCD guy that I am, I went ahead and ordered a new TPS and used MAF at the same time – to be on the ‘safe’ side and fix all issues if possible.
• Right about the same time (just my luck…nothing can be easy), while driving to work one day, the rear wiring harness dropped down and rested on the rear exhaust heat shield, creating burning rubber. At that point the car seemed to begin to run rough – like it’s missing or running on only 5 cylinders. My immediate thought is that I burned through the wiring harness to the point that wires to/from the PCM were arcing on the metal and causing the engine to miss/misfire. Pulled the harness up out of the way and zip-tied it until I could inspect the damage.
• Now….here’s where I screwed up….. Spent a weekend doing all of the following (I know….dumb, dumb, dumb):
- I uncoupled the rear harness, lifted it to inspect the burned area. The wrapping was burned slightly. Carefully slit the harness wrapping to check on the internal wires to see if any of them were burned through. NO internal wire damage! Carefully re-wrapped the harness in that spot with electrical tape, and zip-tied it safely out of the way of the exhaust manifold.
- Replaced the DPFE with the new Motorcraft one,
- Replaced the TPS (new),
- Replaced the MAF (used one from RCM),
- Replaced IAB/IAC (new) (old one had the black cap broken off – see explanation below)
- Replaced the Throttle Body coolant housing that sits between the IAB/IAC and the manifold body. [I had removed it a couple of years ago when I decided to do the Throttle Body Coolant Bypass as described elsewhere on the forum here. Didn’t think I needed it at all anymore, as it appeared to no longer be of service in any way. I had noticed recently that by removing that housing/body and connecting the IAB/IAC directly to the manifold, it did NOT allow the gas vent/purge/accumulator (?) to vent from the manifold to the gas vapor purge solenoid (or is the venting vice-versa). The throttle body coolant housing has a small machined channel cut into it to allow this venting to occur (and its gasket is made for this too). By bolting the IAB/IAC directly to the manifold, the channel was no longer present, thereby cutting off this venting exchange. So…I mounted it back the way it should be, with proper gaskets mounted correctly.
- And I even replaced the vacuum regulator (on the firewall that feeds the EGR)….a part I had bought new a long time ago but never installed.
• Car still running rough. Meaning....
- Stuttering acceleration (like the engine is missing or running on only 5 cylinders) up to about 2800-3000 RPM, then running smoothly at higher speeds/RPMs.
- When started cold, wants to die constantly once I put it in drive to pull away (does this sometimes too when hot, but not often).
- Poor gas mileage.
- Once the engine is warm, rich/chemical smell, seemingly coming into the passenger compartment. Stinks to high-heaven.
• Work done this last weekend to eliminate possibilities and reverse this issue:
- Removed intake, and verified that all nostrils and channels to and from IAB/IAC and EGR were totally clear. (I had cleaned them thoroughly last year).
- Removed EGR mounting tube from exhaust manifold (the one that sends exhaust pressure from the exhaust manifold up to the EGR and DPFE). Verified ALL passages clear of build up, including the two smaller tubes up to the DPFE.
- Verified EGR working properly under mouth-induced-vacuum (watched the diaphragm pin move and open under vacuum).
- New vacuum hoses installed for the secondaries and its vacuum regulator & canister that mount on the back of the manifold. New vacuum hose that runs between the fuel pressure regulator and the intake (at the end of the rails).
- Loosened all silicone hose connectors on the intake manifold to give greatest flexibility in properly seating the manifold back on the engine, installed it with new gaskets, and verified each runner was mounted perfectly flush (eliminating possible vacuum leaks due to improper/cocked intake mounting). Then re-tightened all silicone hose clamps. (BTW… a new set of silicone hoses and claps were installed on the intake within a few months ago).
- Verified that all plug wires run to the correct coil locations, including the frequently mistaken 5 & 6 wires (used the colored diagram posted in the sticky here on the forum). Checked out okay.
- Car still running the same – rough and crappy.
• So… I decided to re-swap-out some of the parts one-at-a-time (the ones I didn’t throw out) to see if I can pinpoint what is causing the problem. Put the old vacuum regulator back in Saturday, and WOW….it seems to have fixed the problem!! No more rough running, purrs like a kitten and roars like a lion. Running perfectly all day Saturday! Concluded that the new vacuum regulator wasn’t working properly.
• Celebrated too soon. Driving car on Sunday. Midday... it starts running rough again. CE light coming on intermittently. Back to the same symptoms.
By the end of the day yesterday (Monday) it started popping (backfiring?) on the way home.
• One additional, odd symptom to mention (not sure if it is impacting any of this)….. many months ago, while doing some work on the car, the black cap on the IAB/IAC broke off. I wasn’t sure what purpose that cap served, and couldn’t find anything about it searching the forum. So, I put a small amount of electrical tape over it to keep dirt out, but wrapped in such a way as to still allow some amount of venting/vacuum (which I assumed was the cap purpose). I immediately started noticing a whistling sucking sound faintly coming out of the engine compartment, but only when driving and I let off the gas pedal and start deceleration (and only when the radio was off so I could hear it, as it is faint sounding). I assumed it was air sucking into the IAB/IAC where that cap had been. I removed the tape out of curiosity, but the whistling/sucking sound didn’t change in any way. Since changing to a new IAB/IAC (same version with a black cap), it still make this sound in the same way, so it didn’t appear to be related to the cap after all. I thought it might be a vacuum leak elsewhere, but after taking the steps above to eliminate potential vacuum leaks, it still makes the sound in the same way. I don’t remember ever hearing this very faint sound before. This isn’t normal is it, and perhaps I never noticed in the past?
My plan now, is to read the new codes, and proceed from there. Which may or may not include swapping out the MAF with the old one. The fact that the car died when disconnecting the MAF concerns me now that you guys stated it should not happen. Old TPS is gone, so I can’t swap out that one. I am a bit concerned as to any nuances in mounting a new TPS, as I just removed the old one and installed the new one, hopefully getting it on correctly (never had replaced on before). I’m going to spray some WD-40 or carb cleaner around the secondaries to see if there might be a vacuum leak there. I’m going to check for water/oil in the plug wells, as well as the condition of the plugs and gaps. I don’t have another coil pack or DIS to swap. I’ll probably also pull the upper cover and check for any jumped teeth on the timing belt.
Maybe the Ford dealer was right....bad PCM (or bad now that its wires may have arced to the exhaust manifold)???
Sorry about the long winded response, but I know from reading thousands of posts here in the past to expect a bunch of questions, so I tried to answer most of them here.
I love this car.
:wave:
Jim
). In the higher RPMs, every third rev equals like a few microseconds so the miss wouldn't be nearly as noticeable.
