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Discussion Starter #1
Hi, first post here. I'm working on a friend's 94 5.0 mustang, trying to get his issue resolved. The car is mostly stock, it has air pump and egr deleted (no tuning done). He has the vacuum lines plugged and block off plates on the exhaust and intake, and no "simulator" or anything for the electrical harness, so he does have codes related to these. Also he has removed the cats and has an aftermarket exhaust. I believe it is 100% stock otherwise.

The car runs perfect once at full operating temperature. Perfect idle, perfect driveability, etc. But when it's a cold engine start, it has a sligthly rough/stumbly idle and it is basically undrivable. It bucks and misses badly and is barely driveable.

The car seems to be "tuned up" by a previous mechanic that was not able to find the source of the problem, I even went behind the last guy that worked on it and checked all the spark plugs, wires, etc. Distributor looks brand new and I checked under the cap to make sure there wasn't anything obviously bad. Was some corrosoin on the contacts but I cleaned it off. I have cleaned/tested/etc. the following: MAF, IAC, TPS, IAT, ECT. I also tried a new ECT and IAC as I had access to them with no cost. I also ran through the whole procedure of resetting base idle and resetting TPS voltage. I'm not electrical guru but was able to test all the sensors based on info I foudn online and they all tested good based on cold and hot readings for resistance and key on voltage at any scenario where I tested them.

I have tried looking for vacuum leaks with a can of brake cleaner and found none. I'm thinking about doing a smoke test and cold compression test.

I'm also wondering if the EGR delete can be messing up base fuel tables? How would the EGR being disconnected effect the A/F ratio? Does the computer think it is open or closed (I assume closed, which should have no effect...)? If it thinks it's open then it would think there's more air so it would add fuel and it would be rich, right?

Also wondering about O2 sensors, however, I haven't looked at them because I don't believe they are used until the engine is hot, so don't think this could be the issue. Am I wrong?

I have pulled codes but don't recall them off hand. At one point there were a bunch of codes, but I had charging issues that have since been resolved. Since then, I believe the only codes are related to EGR, thermactor (I believe this is also EGR/AIR related), and one for the radiator fan (which is odd because it works on low and high speeds during the self test). Also, it passed the cylinder balance self test (of course, the engine was hot...).

I feel like I'm grasping at straws at this point, but would really like to get it resolved for him. Any help is appreciated.
 

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knowing

when in closed loop, fuel corrections are being stored into long term fuel trims

long term fuel trims ARE applied to open loop

when you cold start, or start any time, it will be in open loop, until conditions are satisfied to go into closed loop

see anything there?

post all engine off and engine running codes, then perform a cylinder balance test after running test codes end

list them out here, code number, and what circuit it represents

this does not assume you might have a air leak when cold that seals as it warms up.

but we will get to that after
 
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Discussion Starter #3
Thanks for your response, sorry it's taken me so long to reply. We've had hurricanes, vacations, holidays, etc. and I just didn't have time to mess with this mustang.

I'm not sure if your post/text got a little jumbled or what but I understand most of what you said. Here are the codes from last time I ran them:

KOEO Codes:
327 - DPFE or EVP circuit below minimum voltage of 0.2 volts (I assume this is due to the EGR/AIR delete and may go away with the plug in tricker thingy)
564 - Electro-drive Fan circuit failure (no idea why this is triggering, when the car does the self test I can hear it run low and high speeds. Not too worried about this one...)

Continuous Memory Codes:
212 - Loss of IDM input to EEC or SPOUT circuit grounded (I had pulled the SPOUT thing to check static timing, this may be why this one was set. Also, I pulled codes multiple times prior to checking timing and this is the first time it's set. So not worried about this one right now, I'll clear them next time I pull codes...)
327 - Same as above

Engine Running Codes:
314 - Thermactor air system inoperative - left side (I assume this is due to the EGR/AIR delete and may go away with the plug in tricker thingy)
311 - Thermactor air system inoperative - right side (I assume this is due to the EGR/AIR delete and may go away with the plug in tricker thingy)
327 - Same as above

Cylinder Balance Test:
CEL flashed 9 times (believe this is a pass)

I'm not sure what you mean "what circuit it represents"...?

I started the car the other day and let it warm up just to charge the battery since it's sat a little while, and noticed while walking around the yard that the driver side exhaust was putting out a little bit of smoke/moisture, and the passenger side was not. Now, it could have been from the weather (been a little colder here lately), which isn't totally abnormal, but I thought it was odd only the driver side did it. Wondering if this could be related to the issue? If it was "smoke" and not just from cold start, it was water I'd say. It was not blue or black, it was closer to white if anything. And the liquid on the concrete (small wet spot/puddle) did not smell like gas, it looked and felt like water.

Thanks for your help, I can pull codes again this weekend. Could really use some guidance on how to proceed troubleshooting.
 

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Discussion Starter #4
I should also note when I first got the car, it had codes:
173 (O2 sensor sensor circuit indicates system rich (right side)
177 (O2 sensor sensor circuit indicates system rich (left side)
556 (Fuel pump circuit failure)

But the car had a charging issue, it wasn't putting out proper voltage. I believe the voltage regulator was faulty, replaced the alternator and VR and it has been charging fine since and these codes have not returned. I believe they were triggered due to the charging issues.
 

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I WILL put a little thought into it later

but to address your question about “not sure what circuit it represents”

if you read the description of the codes 173 and 177 in your parenthesis

see how it says “sensor circuit”? and 556 says “circuit”

in a nutshell, codes are generated from an out of spec expected value

the out of spec on all codes is a CIRCUIT issue, it can be the sensor or component

a code DOES NOT mean change a part
 

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Discussion Starter #6
Ok thanks. I definitely understand what you are saying lol. I am not a parts changer, and while I'm not the best mechanic in the world I'm a pretty knowledgable diy guy. My buddy brought this car to me to look at after two different professional "mechanics" were unable to fix the issue, and they racked him up a bill by throwing parst at it. I work a lot with OBD2 (this is actually the first OBD1 vehicle I've worked on where I needed to pull codes, so just that was a learning experience), I work a lot on LS engines, and a bunch of misc. stuff here and there. My dad has a supercharged 4.6L modular marauder, I have a 402 stroker LS2, etc. I'm much more familiar with GM engines but know a little bit about modular fords and some modern chrysler engines, just from having them in the family. Like I said I'm not the most knowledgable in the world, but I'm always working on this stuff and I have a good basic understanding of how all the sensors work and what they do, etc. I learned long ago changing parts just lightens your wallet! I appreciate your help with this.
 

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564 the low speed fan is turned off by the ecm, NOT on

if low speed does NOT turn off, its a failed circuit

now lets look at the 02s

if both banks are always rich, the ecm will reach leaning out limit

these short term trims will produce long term trims

when applied at start, OL will have fuel pulled, and the engine will be lean, a cold engine needs alot of fuel

time to check if the 02s are lying

you can measure 02 signal voltage at ecm, by backprobing while engine is at operating temp

measure at tell us what you get
 

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When it misfires cold, is it popping through the intake?
 

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Discussion Starter #10
I'm not sure. It just sort of has a rough idle, not really a clear misfire. It sort of like almost stalls then catches itself and repeats. But if you try to drive it it pops and stumbles really bad when giving it gas. But I don't know if it's misfiring back into the intake or not.
 

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THAT is a yes
most likely lack of fuel
 

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Ok, so I let it warm up today and checked voltage at the ecu on the O2 sensors. Once fully warmed up and running smoothly, I had the below readings:

Left = 0.98
Right = 0.88

Both were bouncing around a couple hundredths, but pretty steady. During warmup, they were all over the place, anywhere from 0.1 to 0.9 volts, bouncing around rapidly and was hard to even follow.

I took some videos too, if I can figure out how to upload them I will, or maybe upload to youtube and paste links. Once the temp gauge hits the "N" on "Normal" it's like a light switch is flipped and the car just smooths right out and runs perfeclty.

Unfortunately, there's another issue that I thought I had previously resolved. It is not charging again. I thought the voltage regulator was bad so got a new alternator/VR under warranty which seemed to fix the issue. Well today it was only putting out ~11 V the whole time it warmed up. Once it smoothed out and was running good it steadily decreased to where it was only putting out ~8 V. All the gauges froze, etc. and I shut it off. I'll have to charge the battery up and figure out what to trouble shoot there also.
 

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If the voltage was fixed near 1volt when warm, that means the 02s are reporting a rich condition

what we have to do, see if they are lying or not

we need to introduce more air, and see if they can go lean

we can create a large air leak, like unplugging the booster, or unplugging a injector on both banks WHILE watching the 02s voltage

do they go lean? ie go ro 0 volts
 

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Discussion Starter #14
Gotcha, so 1 volt = rich, 0 volt = lean, and I'm guessing 0.5 V is stoich and ideally where it should be?

I'll work on this tomorrow evening or this weekend. Gotta charge the battery up too. Any insight on what to look for with the charging issue? The alternator and VR is brand new, and it was doing the same thing with the last (new) alternator. Seems to be an intermittent charging issue.
 

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it should be oscillating between 0 and 1 volt many times a second, never steady at any voltage
 

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Discussion Starter #16
Ok thanks. Here's some videos that might show better what I'm trying to explain:

Warming up right after cold start:

Warming up right after cold start (I hadn't noticed yet that it was only charging ~11 volts):

Warming up right after cold start, giving it just a little gas so you can hear the pop/miss:

Warming up still, but closer to fully warmed up, starting to have periods of "smooth" running for a couple seconds:

Pretty much fully warmed up, suddenly runs perfectly smooth:
 

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you have no 'batt' light on...............

does it come on during the bulb check ?

bulb is part of the charging circuit, and must work
 

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Discussion Starter #18
No sir it does not, I just checked. I'll try replacing it and see if that resolves the issue. I will create an air leak and check O2 sensor voltage sometime this weekend also.
 

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before you go and tear out the dash for one bulb

trace it to the battery, and ensure the ground is there
 

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Discussion Starter #20
hm, ok. I may have to hunt for a wiring diagram, unless you know which ground I should be looking for?
 
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