86 Iroc, 305 tpi. The fuel pump went bad, causing low fuel pressure that bled off quickly, and got to the point where it would not run at all, so i parked it over the winter. I just replaced the fuel pump and injectors with bosch 3's from southbay, and now the car starts but runs VERY rough, backfires through the intake on occasion under throttle, and i STILL have to feather the throttle to keep it alive. Fuel pressure is now where it should be, 43 psi key on engine off, and about the same when running. I figured i would check my plus and wires, even though they were less than 6 months old. ALL of my AC Delco R43TS plugs were carbon fouled. just black and smelled like fuel. Next thing i did was inspect all my plug wires, which are Jegs Pow'r 8mm wires. All tested good on my multimeter, but i ordered a new set anyways, since 1 of them did have a burn on it that caused some minor cracks. Enough to probably let some spark jump out. Next, I inspected my cap, rotor, and measured resistance values of the dist. pickup coil, and the ignition coil. Resistance vaules were in spec. My rotor, however, was a cheap duralast and had serious carbon tracking all around the inside near the metal strip. It also appears slightly bent to one side. I switched out the rotor, and put everything back together. I am waiting on my new jegs wires to come now, and will once again put a new set of AC R43ts plugs in and see what happens. My question is, how do you think my plugs are fouled like this when my original problem was LOW fuel pressure? Fouled plugs are caused generally by a rich condition, or weak ignition system right? Do you think my rotor could have been the problem since it had alot of carbon visible and the strip was bent? Is this the incorrect plug for a stock 305 tpi? Plenum gaskets were replaced when I changed the injectors. This car ran good before the fuel pump died! Thaks! P.S. Sorry about the iphone low res pics, and my fingernails.

 

Oh and some of you may have seen my other post from a week ago about me not having enough gas in the tank and that was why it wouldnt start initially after the fuel pump replacement lol. Sending unit is way off. PLENTY of fresh fuel now. So....yeah.

 

Your motor calls for the ACDelco R45TS (not the COLDER) R43TS that you are running. A hotter plug will burn away most of that carbon build-up!

 

Thank you sir for your reply, I will get the 45's tomorrow. In your experience, have you seen fouled plugs cause backfiring?

 

Are they the correct injectors? 305 should be 19#/hr.

Fuel pressure at 43 psi key-on, engine-off is OK. But should drop somewhat with the engine running. Is the vacuum line connected to the FPR? It may also be that the FPR diaphragm has a tear in it.

RBob.

 

I can't say for sure, but the way those plugs looked, a new set can't hurt. Also get a bottle of Chevron Techron gas treatment and run it threw a full tank and take it out on the highway and floor it several times (if NOT backfiring) and see how much crap comes out the exhaust. Make sure to check the factory GAP setting on the plugs before install (I believe it is .035) Last but not least, have you checked your timing?

 

The R43TS is actually the right plug for that car.

I'd check the engine ground, and check the coil.

 

Yes, I ordered the 19lb injectors, I hope that's what I actually got!! So the 43's are the right plug? Thanks, I'll make sure to double check with the part's counter guy. Have not checked timing yet, but will. Just strange that the car ran good before the fuel pump died, and now the plugs are fouled like this. Thanks again guys.

 

Your backfiring could very well have been caused by the carbon tracking on the rotor. That is an often-overlooked cause of problems. The even-ness of the fouling on your plugs suggests that there is another problem.

Why did you replace injectors if the car was running well? The problem with making multiple changes simultaneously is that it makes it difficult to trace problems should they arise. I would have replaced the pump, and then after seeing the engine run satisfactorily, I would have continued with any other upgrades.

Are you getting any codes from the ECM?

 

Yeah the rotor had way more carbon buildup than I have ever seen. I know that's not good as the spark will tend to follow the carbon track. Do you think that all my plugs could be fouled because of this? My thinking is that if the rotor is defective, that will cause weak or inconsistant spark to ALL cylinders, leading to inconsistant firing, incomplete combustion. Backfire possibly from cylinders loading up on fuel then burning off when the cylinder(s) get good spark? I changed the injectors because I believe some were leaking down. I say this because after the car would sit overnight, I'd start it up an it smelled rich as heck and would often have longer than normal crank time.

 

Well, it's hard to say, but maybe. Carbon tracking can lead to a complete no-start, so I guess so... but if it were inconsistent, I'd expect uneven fouling of the plugs.

That said, I'd start with a new rotor and a new set of plugs and see what happens.

 

I would also check to see if the coil ground strap is there. I cant remember what the end result of that missing is, but it has to be there.

 

I think we may be on to something here.....starting was getting harder and harder and i attributed it to the fuel pump all this time since i tested it and the pressure was low and bleeding off almost instantly.....wonder if at the same time my pump went bad, the rotor was devolping this problem.

 

Whoa... that's an important piece of information that you did not share before... did you check your spark? A weak spark would cause carbon fouling, and it would make sense with all the other symptoms (except for the fuel pressure issues).

Your spark should jump a 1/4" gap at sea level pressure, and be bright blue. If it is yellow or intermittent, you probably have a bad ignition coil. A coil can seem to be OK when you measure resistance, but it has two internal coils, and if either one is shorted, even for just a couple of windings, it can cause a weak spark or even no spark.

 

yeah sorry, the car did sit all winter and i forgot some things until now when i really started thinking about it again. Funny how things come back to memory. I'll let you all know in a day or so when my new wires arrive, if after changing the rotor, plugs and wires fixes it. If that dont fix it i guess ill try a new coil. When you say two internall coils, you mean the primary and secondary right? If so, i did test the resistance of both, and one tested infiniti, but the other within spec. Book said only to change the coil IF BOTH tested bad. I thought that was wierd...... Is the book wrong?

 

Yes, I meant primary and secondary. The coil is a transformer. It steps 12V up to about 50,000 Volts. Therefore, the ratio between the two is considerably large. The primary will have significantly fewer windings, hence, it will read with a little resistance, but the secondary will have a much higher resistance.

Testing the resistance of the coil doesn't give you an absolute indication of its functionality. It is really more to make sure that you don't have an open winding. All it takes is a short in one or two windings of the coil to reduce the functionality of the coil to the point where you have spark, but it is weak.

This just happened to my son's car, BTW. He broke down on the road, and the car sounded like it wanted to fire, but wouldn't. When we tested the spark, it was there, but it was yellow, somewhat intermittent, and had trouble jumping a 1/4" gap. We changed the coil, and she fired right up and ran normally.

 

Thanks for your input sir. As soon as I get the plugs and wires in, I will check the spark with my spark tester. I am also changing out my o2 sensor because I don't know how old it is.

 

fix the main problem first, go buy an msd coil there cheap enough. check spark before and after mine did the same thing because of a bad advance in the distribtor.

 

was there ever a fix to this problem ?????