Backfires - allmost

[slownis]

I acquired my '92 Ranger last week and have already put some cash into it to make it driveable. It firstly needed a new battery. My next problem is the CEL. I pulled the codes and got 157 and 158, which pointed me to the MAF sensor. I followed the directions on this site and bought some tamper resitant torx bits and cleaner so I could clean the MAF. It did look a bit dirty, but the CEL is still on. It drives OK, but stumbles a bit when idling. Occasionally when on the road it will give a buck and a sort of jerk, almost like a backfire that you can't hear.

A previous owner had installed a drop-in K&N air filter. I pulled it out and it is nasty! So my next step will be to buy the K&N cleaner kit and clean it. Could that be causing the CEL and backfire issue, or am I going to need to purchase a reman MAF sensor?

 

[09ajmaros]

that bad filter is probably choking the engine and causing the computer to shoot those codes but clean the filter and see if that's it, you have to start some where

 

[betomonroy]

At the same time remove and clean the throttle body. You will be surprised. When the throttle body is dirty with sludge on the back of the valve it can get clugged and at idle it WILL be choking. This also creates a terrible city mileage and low RPM at idle.

 

[slownis]

At the same time remove and clean the throttle body. You will be surprised. When the throttle body is dirty with sludge on the back of the valve it can get clugged and at idle it WILL be choking. This also creates a terrible city mileage and low RPM at idle.

Well, I looked at the throttle body and it is built into the upper intake manifold, which is more that I want to get into right now. I pulled off the intake hose and cleaned it out with a shop towel and brush as best as I can. It was black and oily in there, but I don't think that is the problem.

Update: I recharged the K&N air filter, which looks much better now. Unfortunately, after this and all of the above, it is still throwing the code. I went through the MAF sensor diagnostic for testing the MAF that is provided on the MAF cleaning procedure that was so nicely provided on this site. So now I think the MAF codes I have been getting is more of a symptom of the real cause of my issues.

What I noticed is that my truck would idle fine for a while, and then start missing out, idle rough, and try to die, so the computer would open the throttle up a bit and it would rev up and the idle would be OK again for a while. I think they call this 'cycling'.

So while I was testing the MAF voltage with the engine running during this cycling, when it was running good, I would get around 1 volt, a good reading. When it would try to die and almost quit, naturally the reading would drop to zero.

So I think my next step is to pull out a few plugs to look at them and go from there.

 

[Wicked_Sludge]

next time the truck is idling rough, unplug the MAF sensor. if the sensor is sending false signals to the PCM, unplugging it will cause the PCM to ignore the sensor and run without it. if the engine smooths out any with the MAF unplugged, it could be faulty.

i dont forsee bad plugs causing an intermittant symptom, they are either good or bad.

 

[slownis]

I did try that, and saw no change in the idle. Plus, I don't think you read my previous post where I hooked it up to a digital volt meter. It sure seemed like the readings were a reaction of the fluctuations in idle, and not the other way around. After reading around a bit, I'm thinking vacuum leak? I dunno, my little 1.8 Eclipse is a heck of a lot easier to diagnose. (more likely that I'm just more used to it, after owning it for over 10 years. Ford is a new ball game to me).

 

[Wicked_Sludge]

a vacuum leak would also cause a pretty steady symptom, not an intermittant one.

intermittant electrical problems are tough and i think this one has me stumped. i want to condem the MAF, but it seems to be operating properly.

 

[slownis]

Well, perhaps my description wasn't really spot on. I originally posted before I had really paid attention to what was happening at idle. From the minute I turn the key, its evident there is a problem with the idle, especially if the truck is already warmed up. It does have a sort of cycle to it. It will go from a fast, even sounding idle, to a loping, missing out kind-of idle (where it sounds like 1 cylinder isn't firing or something), to just about dying, and then when its just about dead the ecu kicks open the throttle and the cycle starts over. This is all in a span of 30 seconds or so. I could take a video of it and it would probably help.

I also need to add to my list of problems a coolant leak. Its not a steady leak, I can watch under the engine and rev it and not see a drip. Its only happened once since I got the truck last week. I had topped off the radiator when I first got it, and never noticed any coolant smell while driving it on a few short trips. Well, on Sunday I drove it about 30 minutes on the highway. After it sat parked for about 4 hours, I started it up to come back home and smelled the coolant from inside the cab pretty strong, during the first 10 minutes or so of the drive. I checked it when I got home and it was half a bottle low. I'm thinking its the water pump from experiences I've had with other cars, but don't know for sure yet.

 

[Wicked_Sludge]

if its running rough all the time, then a vacuum leak is a possibility. it would have to be a pretty big leak to cause a MAF code to trip i would think.

i dont suppose the rough idling happens to coincide with the a/c compressor cycling...

 

[slownis]

if its running rough all the time, then a vacuum leak is a possibility. it would have to be a pretty big leak to cause a MAF code to trip i would think.

i dont suppose the rough idling happens to coincide with the a/c compressor cycling...

Nope, I didn't have the A/C on at the time.

 

[Wicked_Sludge]

the a/c compressor cycles when the vents are in defrost or defrost w/floor.

 

[slownis]

the a/c compressor cycles when the vents are in defrost or defrost w/floor.

Understood. I know a little about A/C, I've replaced compressors and accumulator/dryers on a couple cars and converted from the old r12 to the new r134a on my Eclipse. I even had to remove the evaporator on my Xterra once when I twisted off the plastic heater hose inlets in one of those dumb moments. It was definitely not related to the A/C. If I can get my video camera to work I'll try to take a video of it later today.

 

[slownis]

So I got some autolite platinum plugs for her, are those any good for these engines? Anyways, I took out the O2 sensor today, and it was a bit black, but nothing obviously wrong with it, so back in it went. I pulled out all the the old plugs and did a compression test. Here are my numbers. Any opinions on them?

1 - 150
2 - 147
3 - 143
4 - 141
5 - 148
6 - 135

Seems OK, although #6 is the lowest by far. The #3 spark plug wire boot came off real easy, so I'm hoping maybe it just wasn't making good contact. I'll know for sure when I get the new plugs and wires in some time this week.

Thanks!

 

[Wicked_Sludge]

autolites are good. they are OE parts. those compression numbers are acceptable.

 

[bumbleb77]

Causes for engine backfires

Some of the things to look at for engine backfiring are faulty emission system, secondary ignition malfunction, fuel injecter problems, vacuum leak at the throttle body, intake manifold, or a loose vacuum line, sticking valve or just in case, crossed plug wires.