1995 3.8 barely runs, black/gray smoke - Ford Mustang Forum
 
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post #1 of 10 (permalink) Old 10-05-2010 Thread Starter
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1995 3.8 barely runs, black/gray smoke

1995 Mustang coupe, 3.8 V6, 5-speed. The car starts but runs horribly. Loping and emitting blackish/grayish smoke like it's loading up on fuel. It will rev but it doesn't "clear out" like a flooded, carbureted engine will. The "check engine" light has not come on at all and there are no codes. Currently, fuel pressure is running 34-40psi, but I've seen it drop below 20psi at times. Changes in the pressure don't seem to corelate directly to the way the engine is running. A new air filter and fuel filter were installed with no effect early on in the process.

Any thoughts or input are greatly appreciated.


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post #2 of 10 (permalink) Old 10-06-2010
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do a compression test all cylinders. if that fails do a leak down test to see if you have some sticking valves, rotate crank manually to were both valves are closed to perform leak test on each cylinder one at a time if you have an aircompressor. valves may not be closing all the way. exhaust side that is.

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post #3 of 10 (permalink) Old 10-06-2010
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It sounds more like an electrical issue. When were the plugs, wires, and coilpack changed?

Changes or drop in FRP are often signs of a stuck injector......

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post #4 of 10 (permalink) Old 10-06-2010
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My 2 cents worth. How was the fuel pressure measured? If measured with an external gauge at idle, fuel pressure in the 20's is not all that low. Remember that the fuel pressure is intake manifold referenced and at idle, the intake is under a vaccum.

Check the fuel return line for blockage or kinks.

For a test, remove and plug the fuel regulator vacuum reference line. The external gauge and the regulator should now read the same. For the Mustang, the pressure should be 40 PSI. Rev the motor to see if fuel pressure remains around 40 PSI. Never drive the car with the reference line disconnected.

Check the fuses.

Have you cleaned the MAF? What happens if the MAF is disconnected? Does it run better?

Do you have any exhaust leaks?

How old are the O2 sensors?

Confirm there is spark in all cylinders. Need to know if the chronic rich is because of no spark or the PCM is calling for too much fuel.

Buy/rent a set of "noid" style test lights. Place across each injector to confirm "firing" pulse. The light will flash with each PCM pulse. Look for any injector with a constant light.

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post #5 of 10 (permalink) Old 10-06-2010 Thread Starter
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Thanks for responses. I'll certainly be looking at some of the things suggested. This problem began intermittently, and at first seemed that hot soaking would trigger it. I actually drove the car to work on Monday morning and back home at lunch (it's only 3 miles one way), but 30 minutes later it wouldn't run worth a crap. Since then it's been nothing but crap.

Fuel pressure was measured at the schrader valve on the fuel rail. With key "on" the pressure is 34-36psi. Repeated cycling of the key "on" and "off" will raise pressure to 40psi. Start the engine and pressure remains constant at idle. Rev engine and pressure rises temporarily. Remove vac line from regulator while running and pressure rises. I think the pump and regulator are operating within acceptable parameters, at least at this time. Earlier testing that gave the 20psi reading actually seemed inconsistent and the tests I've done the last couple days have been fairly consistent. There could still be an issue here, but it's not showing itself right now, and it still runs like crap.

The MAF looked clean, but just to "cover the bases" I sprayed it off with the proper mass air sensor cleaner. I also unplugged the sensor at one point to see if the "check engine" light would actually come on, which it did on the second run cycle. I believe that this is the way the system should work. I'm actually quite surprised that the light hasn't come on otherwise, with the nasty stuff that's coming out the exhaust.

The engine doesn't seem to be missing on individual cylinders. Whatever is happening seems to be affecting all cylinders in general. There aren't any exhaust leaks, and as far as I know the only sensor on the car that has ever been replaced is the cam position sensor. (I became the second owner of the car about 10 years ago but have only put approximately 2000 miles a year on it. Currently it has 106,000 miles on it...for what it's worth.)

I'll post with any further info I come up with. Any ideas and/or input remains welcome!

I thought I wanted a career....turns out I just wanted a paycheck!

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'95 Mustang coupe
'91 F150
'79 Mustang Mini-Stock
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post #6 of 10 (permalink) Old 10-07-2010
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FWIIW, the gray smoke is troublesome. This sounds more like excessive oil in the combustion chamber. The results of a compression test can help narrow this down.

All black smoke is more likely to be an excessive rich fuel mixture.

The fuel pressure measurements taken with the engine off are not much value. To confirm the correct fuel pressure with an external gauge, pull and PLUG the vacuum reference line. The gauge should read around 40 PSI for the Mustang. Rev the motor and verify the Fuel pressure stays around 40 PSI.

NEVER drive the car with the vaccuum reference line disconnected. This is just for a test to make the external gauge read the same as normal air.

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post #7 of 10 (permalink) Old 10-18-2010 Thread Starter
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Finally got the opportunity to get back to the car. While it had been inconsistent in it's symptoms earlier, it seems to be fairly consistent now. It will start and idle, but it's barely ticking over at less than 500 rpm and kind of sounds like it has a super lopey cam in it. It doesn't want to rev and sounds very flat. Try to rev it hard enough at times and it'll pop back through the intake.

Compression test showed all cylinders between 160-170 psi. Fuel pressure has been steady at 38-40 psi and reacts properly upon acceleration. Intake manifold vacuum is very low...under 10 in/Hg and bouncing a bit. Still hasn't set a code or turned on the light at all. A friend who works at a local parts store "loaned" me a PCM to try just for the heck of it. Made no difference whatsoever. Disconnecting sensors (MAF, O2, TPS, etc...) had no effect.

While it doesn't exactly make sense with some of the earlier symptoms I witnessed, I'm now wondering about a vacuum leak under the intake or possibly a timing chain issue. Short of some real disassembly of the engine I don't know of a decent way to get an idea of chain stretch on this engine. With a tensioner on the chain, the old trick of observing distributor rotor motion (in this case the CPS rotor) may not be very telling. Of course, if this thing had a distributor and carburetor like engines were intended to have, I would have had it fixed the day after it messed up....if it would have messed up at all! LOL

Does any of this make sense? Any thoughts?

I thought I wanted a career....turns out I just wanted a paycheck!

'70 Mach I
'95 Mustang coupe
'91 F150
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post #8 of 10 (permalink) Old 10-18-2010
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FWIIW, I think you have a major vacuum leak. The good compression results tends to rule out a piston/valve issue (or at least make other possible sources more likely).

A byproduct of the very low intake manifold vacuum is HIGH FUEL pressure. IMO, this is a possible source of the excessive fuel (rich). Remember that the fuel pressure is intake manifold referenced. So if the intake vacuum is low, this will raise fuel pressure resulting in a RICH mixture.

Have you ruled out a vacuum leak at the power brake booster? What other tests have you done to locate a vacuum leak source? EVAP? EGR? PCV?

Consider getting a propane based leak detector. IMO, it's a bad idea to spray carb/choke cleaner all over an engine looking for vacuum leaks because the solvents could damage gaskets. This is trading one problem for another.

Amazon.com: Vacuum Leak Detector: Automotive

However, I still suspect this is a sizeable vacuum leak.

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post #9 of 10 (permalink) Old 11-22-2010 Thread Starter
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Okay...it's a month later and the car still isn't driveable. As pointed out by wmburns, I ruled out other possible external sources of a vacuum leak (brake booster, EGR, EVP, etc) and decided to just do some "exploratory surgery". Replaced intake gaskets and also inspected and replaced the timing chain. The original timing chain exhibited deflection very close to the specified limit.

Now that it's reassembled, the engine starts fine (cold start) and comes up on fast idle for a bit before dropping to idle rpm, just as it always had. After running okay for a bit (15 seconds or so) at normal idle it will start skipping just a little and gets worse and worse until it either just shuts off or gets so rough it just can't maintain rotation. Fuel pressure seems pretty constant between 38-40psi and still am not getting a check engine light.

Just for kicks (and since I could) I borrowed a crank position sensor and gave that a shot. Had nothing to lose but obviously it didn't help.

I obtained a Mac tools MT97 scanner that I've attempted to use but I haven't been able to get any info out of it (supposed to be able to read data streams with it). The vast majority of the fields on the screens say "not supported". Figures.

At this point, unless a brainstorm appears in the very near future, I'm going to have to pay someone to tow the car to a shop (already paid once to get the car home) and then pay someone else to fix something that I could do myself if I only knew what to fix!! I find it quite frustrating but around here automotive techs don't make service calls, so getting one to come to my garage and do the diagnosis so I can make the repair is out of the question. I work at an agri/industrial dealer and we make service calls all the time, but comparing the two industries is a subject for another thread.

If anyone has any final thoughts, directions for use of MT97 scanner, or anything else that might be considered useful information or queries for further information, please feel free to post up!

I thought I wanted a career....turns out I just wanted a paycheck!

'70 Mach I
'95 Mustang coupe
'91 F150
'79 Mustang Mini-Stock
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post #10 of 10 (permalink) Old 03-30-2011 Thread Starter
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Finally! Four months after my last post I have a resolution to the problem. I actually found someone with the knowledge and equipment that was willing to come to my garage and do the diagnosis. He connected his $9000 scanner to the car and determined that the MAF sensor had issues. Replaced the sensor tonight and we're back in business! Cost for the service call diagnosis...$35. Wish I could have found this guy months ago!

I thought I wanted a career....turns out I just wanted a paycheck!

'70 Mach I
'95 Mustang coupe
'91 F150
'79 Mustang Mini-Stock
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