Intermittent rough idle on warm start....

[2stroke]

If you are qualified to change spark plugs, you are qualified to clean fuel injectors. Its easy as pie, especially since you don't have to deal with the egr tube. you have to move some wires and things out of the way, but other than that its mostly unbolt the plenum, unbolt the fuel rail, and there it is. I've done it in a parking lot in 30 minutes. If you want to avoid doing it in a parking lot, make sure you put the fuel injectors in the fuel rail first, then guide them into the head. If you do it the other way around, you can screw up the o rings. All you need for the job is plenum gaskets at about $10, and a couple bucks for injector o rings. Tools are just basic except you need a socket torx for the fuel rail studs. I bet you could do the whole job with a flat screw driver, a 13 mm socket with extension, and whatever size the torx socket was. While cleaning your fuel injectors will certainly help it run better, I don't know if it will fix the intermittent rough idle. I've never fixed mine. There is a super easy test for the TPS if you have a volt meter, and if you are willing to spend a little time, you can actually adjust them. I think OEM tolerance is pretty large, something along the lines of .8-1.2 volts. For peak performance, I think it should be .94-.98 volts. Don't quote me on those numbers, but if you ream out the two holes, you can actually turn it to adjust it perfectly. Your IAC won't cause this problem. It simply affects what speed your engine idles. At. You could clean your MAF if you haven't already. Like I said, I've done all these things with no change to the rough idle. Normally it idles ok, and runs great. They never idle silky smooth. What I think it is, is a simplistic computer. When you go to start it up, it either senses hot or cold start. This is just a guess. When it senses cold for whatever reason, it dumps too much gas at start up, and idles poorly until you clear it out. There is no fix for that, if that is the case.

 

[natenkiki2004]

If you are qualified to change spark plugs, you are qualified to clean fuel injectors. Its easy as pie, especially since you don't have to deal with the egr tube. you have to move some wires and things out of the way, but other than that its mostly unbolt the plenum, unbolt the fuel rail, and there it is. I've done it in a parking lot in 30 minutes. If you want to avoid doing it in a parking lot, make sure you put the fuel injectors in the fuel rail first, then guide them into the head. If you do it the other way around, you can screw up the o rings. All you need for the job is plenum gaskets at about $10, and a couple bucks for injector o rings. Tools are just basic except you need a socket torx for the fuel rail studs. I bet you could do the whole job with a flat screw driver, a 13 mm socket with extension, and whatever size the torx socket was. While cleaning your fuel injectors will certainly help it run better, I don't know if it will fix the intermittent rough idle. I've never fixed mine. There is a super easy test for the TPS if you have a volt meter, and if you are willing to spend a little time, you can actually adjust them. I think OEM tolerance is pretty large, something along the lines of .8-1.2 volts. For peak performance, I think it should be .94-.98 volts. Don't quote me on those numbers, but if you ream out the two holes, you can actually turn it to adjust it perfectly. Your IAC won't cause this problem. It simply affects what speed your engine idles. At. You could clean your MAF if you haven't already. Like I said, I've done all these things with no change to the rough idle. Normally it idles ok, and runs great. They never idle silky smooth. What I think it is, is a simplistic computer. When you go to start it up, it either senses hot or cold start. This is just a guess. When it senses cold for whatever reason, it dumps too much gas at start up, and idles poorly until you clear it out. There is no fix for that, if that is the case.

2stroke, you never actually said how to clean the injectors. I'd be willing to bet that without putting them on a cleaning machine, you're not doing much. They need to be checked for flow rates and leaks. Especially these batch fire systems, one bad injector can foul up a whole bank. If one leaks and causes a misfire, the computer would see that unburned oxygen and dump more fuel in. This is just my theory but it seems to make sense.

 

[2stroke]

I don't know how I completely skipped that part. I'm sure there is a better way to do it, but I basically run cleaner through them. I get a piece of hose that fits tight on one end, and hook it to a syringe full of cleaner. I usually use carb cleaner because thats what I have, but there are plenty of fuel system cleaners that will work. I use a 9v battery with 2 wires on them with female spade connectors. First I let the injector soak in a bowl of cleaner for a few minutes, then I put the hose/syringe full of cleaner on the top side. I hook up the spades on the injector, but leave one wire off the battery, and put pressure on the syringe. Then I tap the wire on the battery to actuate the injector. You can spray it backwards too. This is the poor mans way of doing it. Honestly, if you were going to go through all the trouble and money of having someone clean them for you, checking them for leaks and such, I would just buy all new re-manufactured injectors. Brand new ones are very expensive at $40 minimum, motorcraft I bet is close to $100 each, but remans can be had for $25 each.

 

[arco777]

2stroke, I use a method like yours. I soak mine overnight in injector cleaner, then blow through them while pulsing 12v to them. I use a test harness made from gator clips, a momentary switch and an injector connector. I made my intermittent rough idle go away for good on one Explorer this way.

 

[2stroke]

What do the injectors normally get for volts? I used a 9 volt battery, and it worked, but maybe a 12 v would be better?

 

[arco777]

I haven't found a solid answer for the voltage that they use. I'd use the lowest voltage that opens them. 9v should be fine. I think they're a simple electromagnetic coil, longer duration of being open is probably worse than a couple extra volts.

I know I did use a 12v bulb once to test that the PCM was firing the injectors, and it lit just as brightly as when hooked to a 12v source.

 

[2stroke]

Hmm, I should pop off one of the connections and put the DMM on it to figure it out once and for all. Cylinder 3 fuel injector should be easy to do without removing anything.

 

[arco777]

I'd think an analog voltmeter would work better unless your digital has a peak hold. These are pretty short pulses.

 

[natenkiki2004]

You CAN clean them that way but you still don't have a way to verify that all 6 are flowing evenly which is important. I should have worded my post better, I wouldn't get a set of new injectors for 2 reasons and the first and most obvious one is cost. Other reason is that who knows how long they've been sitting on a shelf. If you go to any reputable injector rebuilder, they suggest installing the injectors within a week and they put oil in them before shipping. Getting them through a rebuilder is best since they have the proper machine and can get 6 injectors that flow the same.

 

[2stroke]

Yes, my Fluke meter will work fine, and I'll post the results if I get them.

natenkiki2004- Shows how much I know about a proper injector job. I pull injectors from wrecked trucks in junk yards and put them in my own. My engines do last though. I don't expect perfection from these. I wouldn't buy a 90's ford truck if I did. I say forget the stumble, and focus on keeping the engine healthy.

 

[Wolfie_85]

I had my other car do the same thing because of the gas I used (only happened with gas from one local station). Not sure what it was about it, but starting it warm, it ran like crap. Ever try switching brands? Just a thought. Perhaps not likely the cause, but you never know.

As for the injectors, they do probably need attention at this age. Been thinking about doing mine. Should have thought about it when the head gasket was being done. Oh well.

 

[arco777]

I don't think injectors are as touchy as some retailers/rebuilders make them out to be. I've ohms checked new ones vs 190k mile ones and not seen a difference, also swapped them out and not seen any difference in running. Some do fail but I think most last a long time because Ford doesn't cheap out on electronics. Flow rates might vary a little but these aren't high horsepower motors running on the ragged edge. Likewise our fuel injection systems are simple and not real picky about slight differences in flow. The OHV especially just seems to run no matter what.

 

[natenkiki2004]

natenkiki2004- Shows how much I know about a proper injector job. I pull injectors from wrecked trucks in junk yards and put them in my own. My engines do last though. I don't expect perfection from these. I wouldn't buy a 90's ford truck if I did. I say forget the stumble, and focus on keeping the engine healthy.

Just an FYI, what I say shouldn't be taken as 100% truth. I have little experience with injectors. In all honesty, a fellow forum member RustyJohnson sent me injectors he cleaned in the manner that you described, he didn't even charge me. I was grateful and very pleased to get them. However, after installing them, the engine ran horribly, like it has 2-3 dead cylinders. It would almost die when I put it in gear and shake horribly when idling. Long story short, I put my old ones back in and it's been working since. I don't know if his had stuck after cleaning or if them being the newer style injector (92TF-AA) just wasn't compatible with my 1991 OHV (90TF-AA injector).

I've been wanting to, and probably will soon, buy a set of professionally remanufactured 92TF-AA injectors. From what I've read, flow rates are very important. Coil tests only show that there's continuity. It says nothing about spray patterns or actual volume that flows though in a given time. Both of which are pretty much the only important test for injectors.

The reason I'm digging into this thread so much right now is that I'm getting misfires when hot and idling. Cold starts are great, plenty of power while driving, no check engine light. I feel like there's a heat soak issue with the injectors, something affecting spray pattern or perhaps even straight up leaking when warm.

The bodies of the injectors can crack, the 1991 & 1992 Explorers came with an older pintle-style injector which is more prone to deposits and spray pattern issues. There's really no lubrication in gasoline and the pintle has to set back on something to seal, maybe that seal is just toast or maybe the spring inside is weak. After 230,000 miles and 23 years... who knows?

 

[smegun]

seem like evey other time i fill up with gas even though using high test i get some cycling like what were talking here after warm there seems to be a poor idle this reflects overall
perfomance at the pedal also seems like you have to kick it to get a good transition of speed like in traffic also .... i want to look at the tpm myself also as well as check the regulator and gas lines im curious about the return line and flow rate changing the screens in the injectors sounds great too

 

[Rupert8]

Hello again,

Well I decided to change out the fuel injectors, using instructions and advice posted elsewhere on this forum. It has seemed to do the trick. Two months now and running great. Not a particularly difficult job, either.

Thanks for all the input.

 

[Bmoresports]

Check and clean MASS AIR FLOW SENSOR as well as EGR and fuel injectors....

 

[Snort]

OK, my hot start problem was similar to this. Hot start rough idle after it had sat for 10-20 minutes, worse in hot weather, not so bad in cold weather. The only thing that made sense to me was that the Air Charge Temp Sensor was getting heat soaked from the hot engine and cooled back down once it got enough air flow through the intake manifold. I checked the resistance on the sensor and it seemed fine, but the voltage coming through the wiring harness was a bit low. Not wanting to dive into the wiring harness or ECU trouble shooting I took a chance on the easiest thing first and replaced the sensor. It's been a couple months as so far all is well.