I would fix that quick. I had a bad injector on my old Bronco that eventually burned a valve. I guess it was making it run lean in just that cylinder.

 

I pulled out the offending injector and tested it. The injector is working as far as I can tell. Measured it's resistance, shows 15 ohms as do several working injectors, the Hayes manual says they should measure 11 - 18 ohms. Put it back in and still it's not working. I took some voltage measurements at several injectors while the engine was running (realizing that full voltage will not be read as each injector only receives voltage for a "split second"). Measured .3 - .4 volts at idle which increases at the RPM is raised at several other injectors. At injector No. 1 I'm only seeing .1 - .2 volts which does not increase as the RPM is raised. I had thought that each injector was controlled by the PCM individually but according to the wiring diagram in the Hayes manual they are not. It seems that 1, 4, 5 and 8 are connected together (all injectors are connected to a common red wire) and 2, 3, 6, and 7 are connected together. Injector 5 is working (tied to No 1?) and receiving much more voltage than No 1. If they are wired together then this would indicate a bad connection in the wiring harness. Am I correct about the wiring? If this is the case then jumping No. 5 to No. 1 would correct the problem if the wiring shown in the book is correct. I want to sure about this, I don't want to go and fry anything.

Pulling my hair out!

 

Makes ya feel a little bit better to know where to start looking, huh? let us know-hope it's an easy fix for you.

OK-I feel really stupid. I replied before I realized we had a second page going.

 

How did you test the injector open air with fuel or did you just put voltage to it with it in your hand? (be careful open air testing an injector hypodermic fuel injection doesn't just happen with diesel injectors!) You could have some sort of blockage in there try swapping that injector with another one. Have you done a compression test on the motor see what you get then add some oil to the low cylinder and see if that brings it up you might be losing compression in that cylinder and some oil is getting past the rings causing that black spark plug!

 

Took the injector out (removing the number 1 injector involves removing the plenum) and put voltage to it. I did think even though it clicked it might be blocked so I put some compressed air to it and the gas that was in it sprayed out in a very fine mist. I did this about 10 more times with injector cleaner and each time it produced a fine mist spray. This probably isn't the best way to test an injector but sometimes you gotta use what you have. When I tested the injector it produced a nice sharp click, when it's in the engine it makes no clicking at all (the other injectors do). Tested compression last weekend... the lowest cylinder measured 155 psi, the highest was 165 - 170 not bad for a high milage motor I think. I'm still thinking a voltage supply problem at the injector as the voltage I'm seeing at the injector that's not working is lower than the ones that are. Of course I could be totally wrong about this, this fuel injection stuff is uncharted territory for me.

 

Swaping the injector is an idea, but you would have to run it awile to find out. (See if the new location turns black) You could just get a new injector or one out of a junkyard. If your sure about the four injectors firing together, just switch the wires and see if it clicks. I've seen engines that fire spark plugs on exhaust strokes, but I dont understand how they could be firing a fuel injector. It would seem to me the mpg would be teriable. I think I would disable the ignition (pull the coil wire) before trying switching the injector wires.

 

Yeah it doesn't make sense to me either but the wiring diagram in the manual shows 1, 4, 5 & 8 are all tied together by a tan wire and this wire goes to one injector output of the PCM (2, 3, 6 & 7 are tied together by a white wire and go to the the PCM injector output). If the diagram in the manual is correct and there's voltage reaching 4, 5 & 8 but little or no voltage reaching No. 1 then there's a problem in the wiring harness on the engine. I was going on the assumption that each injector was controlled individually but then there would have to be 8 injector outputs on the PCM, the manual doesn't show it this way. I was going to by another injector and put it in but I don't want to spend $70 on a part if it's not going to solve the problem not to mention having to spend another day pulling the plenum back off to change it.

 

Success!!!!!!!!!!!!

Using a couple of clipleads I jumped No. 5 to No. 1... the engine smoothed right out and I can hear that injector clicking away. Removed the jumper, the miss came back and the injector stops working, put the jumper back on and she starts clickin away (the injector that is). Now all thats left is to do a little "rewiring" and I'm on my way! Boy that was a real hair puller!

 

Good follow up!!! Check the connector the contact could be pushed too far inside so it doesn't make contact! Get some of the DEOXIT power booster from radioshack it cleans contacts and leaves a protective coating and supposedly increases the energy flow of contacts. It definately cleans them real good I have cleaned contacts that were so corroded to be almost all the way through and it worked, they have a gold pen that leaves a trace of gold on the contact to keep it corrosion free for a long time! But I haven't tried it yet!

 

I looked at the contacts in the connector before I pulled the injector, I know from fixing things for a living that contacts do sometimes get cruddy or pushed out. Thanks for the tip about the cleaner from Radio Shack, I haven't been there in a couple of years. Anyway I permanently connected No. 1 to No. 5 and she's back to her old self. I don't know where but somewhere in the harness these are tied to a commomn feedpoint and something went bad. I would think that firing 4 injectors all at the same time would be terribly inefficient instead of firing each one individually as needed.

Thanks for all the help.

327,600 miles and still going strong

 

You learn something new everyday. I would like someone on here that understands this to explain it.

 

Yes you certainly do! If I hadn't looked at the diagram in the back of the manual I'd still be thinking the injectors were fired individually. Go figure!

I'd like someone who's familiar with this setup to explain it also. Mine's a '94 and I would imagine they've improved on this type of arrangement by now. Perhaps the later models are individually fired.

 

The system we have is bank to bank. The computer fires the injectors every half a rotation(180degrees) It isn't as efficent as true sequential injection, But it is cheaper!SFI needs more sensors, wiring, etc. You could upgrade to SFI but it wouldn't be worth it unless you were doing a lot of other mods (boring,porting,Blower,etc.) The pluses of this system are easier diagnosing and repair plus less parts to breakdown!