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Discussion Starter · #1 ·
So the water pump started leaking pretty severely out of no where. Got a new Motorcraft one and installed it today. Went pretty smoothly. It was stuck to the block pretty good but a few good whacks and it came right off. Got her all buttoned up and filled with Water Wetter + distilled water for summer. No leaks. The problem is now I have a really bad misfire. Like the car will barely stay running in drive with the AC on. No codes. My cheapo “scanner” and phone app says the fuel system status is “open loop due to system failure”. The plugs and wires are literally less than 1k miles old. No problems whatsoever before the water pump change. The only thing I can think of is that I did move the car across the parking lot with the water pump off the car. It was running for literally less than 30 seconds. Does anyone have some ideas, this is my only car at the moment and I have to go to work misfiring like crazy :/ I can post screen shots of my phone app scanner data if any of you know how to interpret it, I don’t understand the vast majority of it.

What I’m thinking right now is that it’s just running really really rich causing the misfire, based on the open loop thing. But I have no idea what would cause that or even if that’s what’s happening.

Thanks for your time.
 

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Check all the plug holes for water. :)
 
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Discussion Starter · #5 ·
I agree with Grog6...
Thanks for the input guys. I have a new development. This morning driving to work the misfire just randomly stopped and the car ran perfectly! Then all of a sudden it came back after a few miles. My scanner said it went into closed loop when it was driving normally. Now goes back to saying open loop due to system failure. What is going on?! Is it possible when I was draining the radiator I got coolant in a wiring harness or something like that? That this is a connection problem?

I will still check for water in the plug holes this afternoon.

Thanks again.
 

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Discussion Starter · #6 ·
On the way home today misfiring at first then for the middle part of the trip the car ran fine. In fact it felt peppier than usual. Did a WOT pull. Get home, pop the hood (still running) and just looking around for loose connections or whatever I can find. While I’m standing there looking at it I hear what sounds like maybe a relay click, and the idle dropped, and it started misfiring again. Once it cools down I’m going to check the plugs as suggested. Any ideas please share, I’m completely at a loss.

I’ve also noticed some weird idle fluctuations. For instance sometime putting it from drive to park the rpm will go to like 1100-1200 whereas it used to go to like 900. I think it’s idling low in drive. Whereas it used to be like 750rpm now it seems like it’s around 500. So lower idle in drive than normal but higher idle in park than normal.
 

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Discussion Starter · #7 ·
Ok the plugs are dry and look fine. I pulled the EEC fuse and cranked the car. Put it back in and went for a drive. The car ran perfectly for a couple of mins, got back home and was idling in the driveway. Heard a click, like a relay, idle dropped, misfire again. With no codes I don’t see how it could be a sensor, right? What in the world.
 

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Discussion Starter · #8 ·
New update, if you guys want me to stop talking to myself just lock the thread...lol.

On a whim I unplugged the MAF and started the car. Boom ran perfectly, scan tool says closed loop. Plugged MAF back in, bam, misfire, scam took says open loop due to system failure.

So now my question is this: is it harmful to drive with the MAF unplugged until I get a new one in the mail?
 

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Sorry for the silence. Glad you found it, what I was thinking of posting would have sent you down the wrong road!

I wouldn't be afraid to run it with the MAF disconnected. At least unless it started running rough again.

Still odd that it wasn't giving you any codes, at least one(s) for misfire.
 

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Discussion Starter · #10 ·
Sorry for the silence. Glad you found it, what I was thinking of posting would have sent you down the wrong road!

I wouldn't be afraid to run it with the MAF disconnected. At least unless it started running rough again.

Still odd that it wasn't giving you any codes, at least one(s) for misfire.
I went and bought some MAF cleaner and sprayed it down good, the connector too. No change. I’m hesitant to order this $100 part if it’s not going to fix it though ya know? What was your suggestion? I think the no code is odd too...it should have misfire plus the MAF right? Is it possible to have a bad MAF and no code? It threw a code pretty quickly after unplugged it.

Also I can’t find a motorcraft MAF anywhere, only off brands, is there a specific one you all could recommend?
 

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The EEC coolant sensor or wiring is my suspicion. If there’s an open circuit it will read as extremely cold and fueling will go rich. Unplugging the MAF just defaults the EEC to using the base fuel table, I do not believe throwing a new MAF at a problem that cropped up after an unrelated job will solve the core problem.
 

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The relay click and idle drop is the fan coming on; that's totally normal.
The air conditioner cycling does the same thing.
You need something to datalog with; you can chase a dead sensor forever with poor info on what's actually happening.
I use an xcal2 and a laptop; there are cheaper options. :)

If you need a new maf, do an upgrade. Get the maf, airbox, and inlet tube off a 2002 mustang. you need a tune to use it, but it's a good upgrade for the future. Likewise, if you need a water pump, buy the closed vane style for the mustang and drop a few degrees at high throttle values. :)

The most common cause for weird behavior lately have involved the EGR; no one ever gets all 8 pieces of hose:)
 

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Not related to the running problem, but I would put 50% antifreeze in there. It raises the boiling point, and nasty corrosion can form in a cooling system with just water. Actually, it can still form with antifreeze, but it definitely helps.

Al
 

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Discussion Starter · #14 ·
The EEC coolant sensor or wiring is my suspicion. If there’s an open circuit it will read as extremely cold and fueling will go rich. Unplugging the MAF just defaults the EEC to using the base fuel table, I do not believe throwing a new MAF at a problem that cropped up after an unrelated job will solve the core problem.
Thank you. I too have since come to the conclusion that the MAF isn't the culprit. I will look into the EEC coolant sensor for sure. I do know our cars have two coolant temp sensors. One for the gauge, one for the EEC. On my scan tool the coolant temps level off about 200-205 which seems pretty normal/accurate, so my question is this which sensor would be responsible for the info on the scan tool? Whichever one that is, I'm pretty sure is functioning properly. My other question for you, as you can probably tell my automotive knowledge is kind of basic, and electrics is the one area that I completely don't understand like at all. So how would I go about tracking down an open circut? Physically inspecting wires and harnesses for broken jackets/frayed copper? Sounds like quite the task, lol.

The relay click and idle drop is the fan coming on; that's totally normal.
The air conditioner cycling does the same thing.
You need something to datalog with; you can chase a dead sensor forever with poor info on what's actually happening.
I use an xcal2 and a laptop; there are cheaper options. :)

If you need a new maf, do an upgrade. Get the maf, airbox, and inlet tube off a 2002 mustang. you need a tune to use it, but it's a good upgrade for the future. Likewise, if you need a water pump, buy the closed vane style for the mustang and drop a few degrees at high throttle values. :)

The most common cause for weird behavior lately have involved the EGR; no one ever gets all 8 pieces of hose:)
I know what you mean about the fan and the AC and it is kind of like that but more pronounced. After seeing it do it a few more times I think I imagined the "click" lol it will just drop idle and start running very rough seemingly at random. I haven't been able to isolate one thing that produces the effect. After I reset the EEC it will run good for a few mins then it's almost like the AC kicking on but more pronounced, idle drop, and terrible misfire. Then while driving seemingly at random it will clear up and act normal for a few mins...then back to terrible misfire.

I already did the water pump, I wish I had thought about the Mustang upgrade sooner. I did at least get a Motorcraft one for the Thunderbird.





Thanks so much for both of your time, it not very often I cant figure out what's wrong with my vehicles. Been doing my own maintenence/repairs since I was about 19. 10 years ago.

I wanted to add that I've been driving around with the MAF unplugged and the problem hasn't arisen since. It runs great other than when pulling away from a stop it will almost die for a second then go, like when you first touch the throttle. I assume that is normal behavior for having the MAF unplugged.
 

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Discussion Starter · #15 ·
This afternoon I have spent some time learning about my phone app and bluetooth scan tool. Apparently it can data log and I plan to do that tomorrow driving around. I don't understand basically any of it, like what the values actually SHOULD be but hopefully there will be something obvious. I've been reading for about an hour and I'm no closer to understanding what my fuel trims, timing, etc should be. I will post the logs here tomorrow afternoon/evening.
 

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Short term fuel trims are real time correction, long term trims are “learned” correction. 0 is stoichiometric air/fuel(14.7:1) positive numbers mean fuel is being added by percentage(ie .10 means 10% fuel added) indicating lean, negative numbers indicate rich, subtracting fuel.

It sounds like your Coolant sensor is ok, the scan tool uses the EEC one for data.
 

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I wanted to add that I've been driving around with the MAF unplugged and the problem hasn't arisen since. It runs great other than when pulling away from a stop it will almost die for a second then go, like when you first touch the throttle. I assume that is normal behavior for having the MAF unplugged.
With your problem going away with it disconnected, usually this means the MAF is bad since the PCM is relying on TP/RPM/temperature tables to compute fuel delivery and tip-in transient fueling is much harder without MAF data.

To elaborate a little on what Matt said, the short term trims indicate commanded lambda. Lower numbers mean a richer mixture is commanded, higher numbers mean a leaner mixture. 1.0 means stoich (14.7 is only for E0, for E10 it's 14.08). 0.85 means 12:1 (for E10).

In closed loop the system is using O2 feedback to maintain perfect stoich (always 1.0 - regardless of fuel type). Because of the "switching" around that inherent to narrow band O2 operation, you'll see it vary a little - this is normal. it should stay within about 4% of 1.00 at all times.

If it's constantly high, that means the PCM is having to subtract fuel to maintain stoich (commanding a 1.1 lambda to achieve a 1.0 lambda) and you are running rich for some reason. If it's constantly low, conversely it means the PCM is having to add fuel to maintain stoich (e.g. commanding .9 to achieve 1.0) and you are running lean. Over time the PCM will use the long term trims as a scalar to the entire fuel delivery table and you'll see your STFTs return to "about" 1.0. But like Matt said these scale fuel delivery, not lambda, so higher LTFTs mean the opposite of higher STFT values. Multiply the STFT by the reciprocal of the LTFT for what the PCM is doing relative to "normal".

In short, STFTs under 1 - adding fuel - running lean. LTFTs under 1 - subtracting fuel - running rich.

So it's important to look at both sets of fueling trims for both banks to see what's going on.
 

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What was your suggestion?
I was thinking engine coolant temperature sensor, too, specially because its related to the system you had recently repaired. But sounds like that's not it.

I checked through my Ford '95 Powertrain & Emission and my ASE manuals for ideas on why the system would go in and out of closed loop. Didn't find what I was looking for - discussion of why the system would come out of closed loop. Seems to me to be an electrical or electronic problem rather than fuel or air.

Is it possible to have a bad MAF and no code?
All MAF sensors are not created equal. Doesn't mean not being unable to find a Motorcraft one is a show stopper. I replaced mine many years ago but couldn't see giving up the original one for the mere core charge. Subsequently retried it many years later and found it now performed better than the one I had replaced. But I could smell fuel when getting on it. Ultimately the fuel trims were going double digits and performance rough so I swapped it back and using it since. I didn't check or notice if the system went open loop at that time. But it never lit up the Check Engine Light during that time.
 

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I am having good luck with the Delphi MAF I got from Autozone. The 20% discount online got it down to $106 + tax, plus I got free shipping.

One thing I'll throw out there is if you have a code for a while, it is possible to burn out the CE light. It happened to our old '96.

Al
 
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Discussion Starter · #20 ·
I will give a more thorough reply when I get off work but it finally threw a code! P0174 System too lean, bank 2. Does this point at the MAF being bad? O2 sensor wouldn’t make it run this bad would it? I also have data logged two of my trips today and luckily I was logging when the code finally popped up. I’ll reply to you guys after work. Thanks for the help!
 
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