Can someone give me some symptoms of a weak or partially clogged fuel injector(s). Will the symptoms always result in a trouble code? After a little bit of spirited driving my vette will have an intermittent misfire. It will clear itself up in a couple of days of normal driving. This has happened two times now. I have checked plugs and wires. Also not getting any trouble codes. When it does misfire, it will really do it when the convertor locks up around 45 mph at part throttle. Then it will clear up around 65 mph, but will still misfire occasianally at that speed. Does any of this ring any bells for anyone? Thanks for your help. :seeya

The car is a 1991 L98. I know that the title says L89 but I am not able to correct it. Sorry.


[Modified by Runum, 6:39 PM 8/31/2003]


[Modified by Runum, 6:43 PM 8/31/2003]


[Modified by Runum, 6:43 PM 8/31/2003]

 

FI's shouldnt give you a troble code..Take out all 8 spark plugs and look at them, you should see what injectors arnt quite keeping up with the others.Chemicals you add to the taKE 'can' help, but you need to constantly put it in the tank and beat the hell outta the engine.If in doubt about there condition, send them to TPIS and they can clean and balance them for you.An injector not firing all the way will destroy your motor, assumiong this is your problem..Good luck!

 

A scan tool could tell you what's happening during misfires but spark plug condition may reveal the problem cause.

If it turns out to be a bad injecotor or two, send the set to Rich at Cruzin Performance (link on my site). He reconditions & flow tests a set for around $80 or so with 48hr shop time. He will blue print a set upon request for a little extra.

 

Just to add to the mix. I had a short in a wire that caused my injectors not to spray right.

 

This is the kind of ideas and experiences I was looking for. Thanks for your help guys. :seeya

 

I can't comment on your problem...

...But I'd like to know what you mean by "a misfire"...

Is it *not* firing? Or can you hear unburned fuel igniting in the exhaust?

Not trying to be a jerk here (although I am good at it :D ), but are these terms the same???

Some threads here get confusing with common terms being used indiscrimately...

 

Thanks for the question. It is my asumption that I am experiencing a misfire based on the feel of the smoothness of the engine. Mine is stone stock with stock exhaust and about 71,00 miles. The only noise I hear is the roar of the tires. What I am experienceing, may also be called a stumble, a hiccup or whatever other name you want to use. At cruise with the minimum gas pedal pressure needed to maintain constant speed I can feel the engine miss. The miss is very short and quick. Also it is very unpredictable. It may happen once or twice a mile for a few miles and then not do it again.

Where it is really noticeable is right after torque convertor lockup at light to medium acceleration(~45 mph). The RPM's are low at that point and the engine is seeing more load at that time. There the engine will really stumble until I get it on up to about 50-55 MPH.

As I said before this stumbling will happen within a few hours after I take the car out for some acceleration runs. The engine runs and pulls wery well and is very smooth during the runs. Then the gremlin starts kicking in. After a couple of days of normal driving the gremlin goes away.

The engine has AC rapid fire plugs in it. I pulled them and didn't notice anything different about any one of them. I used a lighted hand held eye loupe to really look them over. I also checked out the wires with an ohmmeter but that doesn't eliminate any electircal leaks. I also used dilectric grease on the boots. I just ran a bottle of Techroline through the fuel system. I also replaced the MAP and O2 sensors.

The car has not done any of this stumbling with normal driving once the problem clears up. Only after really putting it through its paces.

Again, thanks for the question. I have a good mechanical background and tools but minimal diagnostic equipment. The questions and suggestions really help in thinking this thing through. :confused:

 

Well, here are a few more things...
What were the #s when you ohmd out the s.p. wires?? Look for one (or more then one) that has an unusually high # compared to the rest..If you think one is arching, go out at night ,spray water with a bottle on all the wires and look and listen-should stand right out..
Another thing (but i really doubt it) is to check for a flat spot in the tps sensor-really easy to do-should take 5 mins or so, but like i said , i kinnda doubt that one.
The 2 other things im thinking is that 'possibly' when you beat on it, you are lfreeing up some dirt and deposits in the intake/and plenum..Then it dirtys up a plug, then clears itself out--- a long shot,but its more then possible..Maybe even a egr sticking?
The other thing is to get some tranny guys in here on this one as im wodering if your tranny runs too hot after beating on it,and runs fine at other times..I dunno?!?!? Im a Fuel Injection specialist, but i wouldnt elimate that possiblity either....
Good luck...Brian

 

IMO an injector problem isn't going to be an intermittent problem. You can check the restance of each injector and check the fuel pressure with the engine off to see if the fuel system is leaking down (the check valve in the FP could cause this also)

 

I'm going to guess it's a valve(s) not seating just right from time to time.
At 71K it's probably a good guess it's valve seat/grind time.
Particularly if it hasn't had a valve job along the way.
These things will run a lonnggggg time but they will start beechen a little sometimes.
Good luck with it.

 

Trust me , you can definatly get intermitent injector problems.And fuel pressure should ALWAYS be checked with the engine running..The pressure isnt always the same at idle vrs. WOT..It usually WILL leak down just cycling the key on and off.It will peak, but it wont stay there.(fuel return line-gas dosent stay in the fuel line, its a continous loop)
I still think he has another issue somewhere along the line.

 

Alright, this is what I know so far. I checked the resistance of all of the injectors, they all checked around 16.5 ohms. I realize they can still not flow propely, but I have at least eliminated this possibilty.

Then I pulled the plug wires out of the car for a real look see. The pass. side wires were routed under the EGR tube, I assume that is the factory routing location. All of the wire looms were melted, so I bent the wires to check for cracks. This revealed a crack in the number 6 wire. Also, there was pretty heavy tracking between the distributor cap and rotor. I am replacing the rotor, cap, wires and plugs. The bottom line is, how do I get the wires past the EGR tube and keep them from getting burned by the heat from the tube? :confused:

 

Lots of places have insulating tape/wrap...Jegs,Summit,etc...
Gald you found the problem!!! :rofl:

 

If you found the problem (and I'm not saying that you didn't), why is a bad plug wire only acting up after you get down on it. Sure, it can be intermittent, but wouldn't it (at least once) have screwed up after driving like the speed-limit-observing, law abiding citizen that all Corvette drivers are? Really silly question here, but when was the last time you changed your fuel filter? It's cheap and easy........ just my nickel's worth.

 

BTW, the plug wires are supposed to run down to the back of the valve covers, wrap around the back corner, up the side of the valve covers, peeling off 2X2 as they progress to the front of the engine. MidAmerica has a complete set of the plug wire retainers by the original manufacturer for just $11. Hope that is at least a little help.

 

I have only had the car for a month and I am going through the fuel and ignition systems and checking things or replacing things I find substandard. I do agree that the wire should give more problems than what I have described so that is why I am not sure that I have fixed anything yet. Good idea about the fuel filter. I am going to check the running fuel pressure also when it's back together.

I do have the wire separators and the wires do go behind the valve cover and up the side. Where things get tight is when they go under that EGR tube. The insulation is there but it is still hot enough to melt the plastic spark plug wire sleeving. I thought maybe someone had figured a better, cooler way to route the wires away from that heat source.

You guys are good though, your keeping me on my toes as I work through this. Thanks for the brain power. :seeya