I've been wrestling with my truck running rough for a while now. It's an '87 with the 2.3 and 5-spd. When it's running rough at idle it will occasionally spew out some black smoke in the exhaust. Today I was checking for trouble codes and when I opened up the throttle I got a nice plume of black smoke. The codes I got during the KOER test were: 41, 34, 13, 72 and 73. All basic maintenance has been done and I installed a new TFI module, because that is what first caused this problem. Also I have the EGR valve disconnected while I troubleshoot this problem.

Anyone have any ideas for me? A better explanation of the codes than my book gives me would also be appreciated.

 

I'm not good with codes, but i Ken is and he'll probably reply aswell. Black smoke usually means your blowing raw fuel out the tail pipe. The easiest thing to start with is a cracked spark plug or a bad spark plug wire. The first step would be to start the truck and let it idle and one by one pull off a spark plug wire and put it back on. If you pull wire off a good cylider the engine will slow down and almost stall, If you find one that has very little or no change when you pull it then thats the problem cylinder. What i've done in the past when i have had a dead cylider is trying switching the wire on the bad cylinder with one on a cylinder that is firing and see if the problem moves.
It's easy and free so i'd give it a shot.

 

Good idea, I'll try it tomorrow. Keep the ideas/information coming. I've been stuck on this problem for a while now, the wife is getting tired of me messing with my old truck all the time...

 

You could also check the fuel pressure regulator. It can spike intermittently, leading to high pressure leading to a shot of extra fuel leading to black smoke.
Look in your code reader booklet for 'clues' on the codes and put them next to the numbers. We all don't have the booklets at hand when trying to deduce solutions from problem descriptions. I *KNOW* I don't have any of them memorized, and refuse to do so.
tom

 

Fair enough, I should post what the book says on the codes.

41: EGO sensor output voltage is always 'lean' during the fuel test

34: EGR fault (I had it disconnected during test)

13: Engine did not return to lower rpm prior to entering goose test (seems to be an IAC related code)

72: MAP sensor has not detected a sufficient manifold vacuum change during goose test

73: system has not detected a sufficient TP change during the goose test

I tested fuel pressure by the way and it seems to hold steady at 40 with KOEO and 32 at idle. Most other sundry tune-up parts are pretty new.

 

I decided to check the timing again and adjusted the distributor a bit. At first the starter wouldn't engage, then it started but ran real rough. After I started it again it idled ok, I didn't see any black smoke this time. I did hear a 'popping' sound coming out of the exhaust though, not too loud. Is that a small backfire, or something else?

 

I replied to your original thread.

 

I took your advice Ken and reset the computer last night. Today I drove my truck around for a while and re-tested it. The black smoke has been replaced by an intermittent backfire at idle.

I got the following codes during KOER just now: 41, 34, 13 and 73. Looks like the same from the other day, with the exception of the map sensor code. Do these codes along with the engine problems (backfiring, black smoke, rough then smooth idle and a dog during acceleration) tell anyone anything? According to the codes I might be looking at EGR and air/fuel mix problems?

 

The 73 indiactes you didn't goose the gas pedal when required.

We already tallked about the 34 & 13 and you need to address the 34 DD11 and the 13 is high idle (KE15), disconnect the IAC, it should stall or have an RPM drop.

The 41 is a O2 issue that could cause the black smoke but vacuum leaks and the disconnected EGR might be causing this one. Drop me an email if you want the pinpoint test.

 

Well lets see, my book says the code 41 Continuous Memory is " No EGO sensor switching detected (1987-90)

This would suggest that the O2 sensor is bad, or maybe you have a bad electrical connector or broken lead to it.

The other codes seem to indicate to me that maybe you didn't do the code pulling routine correctly, or maybe you also have a problem with the throttle position sensor.

The black smoke says to me the mixture is very rich. So things like the O2 sensor & MAF or MAP sensor (which ever you have) aren't outputting correctly to the computer & thus confusing it about what to do about the air/fuel ratio.
So the code 41 kinda fits in here imho.

If you are sure you pulled the codes correctly & did the "goose" test right(code 73), then I'd look at the TPS & see if it's resistance in within spec & is smooth (no rough spots) over it's full range.

On the code 13 it seems to be unhappy with the output with the DC motor that positions the throttle, so you need to look to it, it's electrical connections & wires. It will control the idle speed.

On the code 34, I show two KOER possibilities.
1) Exhaust pressure high, or defective PFE/EPT sensor ( 1985-91)
2) EVP voltage above closed limit (1986-90)

 

From the 34 pinpoint tests I have run so far everything seems ok. The EGR system shouldn't be affecting performance at idle though should it? Also, wouldn't disconnecting the EGR system take any of it's effects away while driving? I did hook the EGR system back up today. From all the tests I've been able to run so far everything looks ok there.

The engine does drop in RPM's when the IAC is disconnected, and it's resistances check out ok.

As for running the test, I've tried to do it right and did open up the throttle when beeped at to do so by my little tester. Also, my TPS is new and operating ok. Today my truck is running really loud, lacking power and backfiring occasionally. I also want to say thank you to everyone who has tried to help me out, I've been fighting with these issues for a while. I don't currently have the means to pay a mechanic, buy a new truck or buy a bunch of parts I don't need. So thanks again, and keep the ideas coming.

 

On reviewing my code book I see that I omitted another code 34 possibility.

4) It says that with KOER, EVAP voltage out of range during self test.
So it seems you have 4 choices on the code 34, three with the engine running & 1 in continueous memory at KOEO.

If you ran any of these tests with the EGR disconnected & any vacuum lines unplugged it could affect the air/fuel mixture & cause the popping in the exhaust.

So I'd put it all back together as it's supposed to be, run the tests, then fix the codes one at a time!!!!

If the EGR was hooked up during this last code gathering, then it says the computer is unhappy with the O2 sensor, the idle motor & MAP/MAF for some reason.

The EGR will help prevent engine ping, if it's operating ok. If you drove without it connected, then you should have heard some pinging.

If you have a MAF sensor & it's dirty, it can cause ping.

So did you have the EGR & everything else hooked up during these last code retrievals????

 

Yes I did hook the EGR valve back up today before doing the latest code test. Previously I had capped the vacuum line, just to see if there would be any difference in performance. There aren't any trouble codes stored in the KOEO test, they are all only during KOER.

My system has a MAP instead of a MAF sensor, it has a vacuum line that hooks into the tee at the top of the upper intake. I suppose they do similar jobs, it even looks alot like a MAF sensor, black box with a connector and a vacuum line. Would the cleaning be similar to the method for cleaning the MAF?

 

No MAP cleaning possible that I'm aware of.

Many of the symptoms you've described sure sound like a MAP system problem.

If for instance you have a vacuum leak, it can cause confused outputs from the MAP to the computer & cause it to think the MAP has sensed a change in the engines load, (it thinks you've opened the throttle) but it's due to a drop in manafold vacuum, due to a vacuum leak somewhere, then the computer begins to set about changing the air fuel ratio, making it richer & changing the spark timing.
You can see the results sound very much like what your experiencing.

So you need to first check everywhere & everything for a vacuum leak. This means a thorough check of ALL vacuum lines, fittings & components that operate by or have vacuum applied & the intake side manafold gaskets as well.

If you determine all is well & you have no vacuum leaks, then you must test the MAP sensor. Here is a helpful link with illustrations, for testing Ford MAP/BP sensors. http://www.kemparts.com/techtalk/tt11.asp
Let us know what you find.

 

Thanks for the info, I'll be checking out the map and the oxygen sensors in the morning.