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tomtom72 · 03-01-2007

L'dawg, When you checked the MAP sensor you checked the electrical plug or you checked the plug and the hose?

The issue could be just coincidence although injector snake oil stuff is not advised...only the Techron stuff from Chevron I was told by a GM tech that that is what GM sells over the parts counter in a rebox.

Ya gotta pull the SES DTC(trouble code) & post up, or look it up if ya have a FSM(by Helm). If ya have or know some one with a scan tool with the correct software pkg for your yr Z you could run a scan and compare your data to the data in the Helm FSM. Section 6E, "Emissions and Driveability" chapter is where the codes are listed and the section has a page with what the scan data of a normal LT5 looks like in closed loop.

Usually he early 90 thru 92(?) injectors are the most problematic...they were designed before the ethanol was added to the fuel. So if you're in that group then the injectors are a prime suspect. The later cars seem to be less susceptable to the ethanol. Only thing with failing/failed injectors: the effects don't go away off idle....they can cause a miss but it's permanent till r & r is done. There are two modes of inj failure: coil shorts and nozzle junk. Shorts cause a non firing = lean cylinder. Junk can be either lean or rich because the junk disturbes the spray pattern....neither condition will necessarily set a "code" (DTC) because the injectors are monitored indirectly by the ECM...via the O2 sensors mostly.

The thing is if your miss is real & only at or just off idle speed then I would ask if it gets worse as the car gets to proper coolant temp? It's kind of okay when stone cold? It's there when cold but gets worse as she warms up? All those point to injector coil shorting....in that scenario the injector's short will get worse the more heat gets to the coil and that's the give-away to shorted coils, the miss doesn't go away rather it gets worse. If it is injectors it will get much worse as time passes...the miss that is.

I would also do some looking at all your vacuum connections and pull the plugs for inspection, oh and do a spark test while you're there. The more you can eliminate in the absence of a scan tool the further all of us might have some ideas to pass along. The scan makes it easy but diagnostics can be done without one....it's just back to basics. Ya know does it smell rich or lean, the fuel filter is new, the PCV's are good, the vac connections are all in place & there is no sucking noises, Your vac gauge says it's not lean or rich. You get the idea, right? Oh, yea the spark test will help you eliminate the wires and coils...ya know pull one at a time when shes at idle?

Sorry to be so long winded about this!

Good luck & post up!
Tom

03-01-2007	#3
tomtom72 Join Date: Dec 2004 Location: Jacksonville, FL USA Posts: 4,609	Re: Did fuel injector cleaner cause problem? L'dawg, When you checked the MAP sensor you checked the electrical plug or you checked the plug and the hose? The issue could be just coincidence although injector snake oil stuff is not advised...only the Techron stuff from Chevron I was told by a GM tech that that is what GM sells over the parts counter in a rebox. Ya gotta pull the SES DTC(trouble code) & post up, or look it up if ya have a FSM(by Helm). If ya have or know some one with a scan tool with the correct software pkg for your yr Z you could run a scan and compare your data to the data in the Helm FSM. Section 6E, "Emissions and Driveability" chapter is where the codes are listed and the section has a page with what the scan data of a normal LT5 looks like in closed loop. Usually he early 90 thru 92(?) injectors are the most problematic...they were designed before the ethanol was added to the fuel. So if you're in that group then the injectors are a prime suspect. The later cars seem to be less susceptable to the ethanol. Only thing with failing/failed injectors: the effects don't go away off idle....they can cause a miss but it's permanent till r & r is done. There are two modes of inj failure: coil shorts and nozzle junk. Shorts cause a non firing = lean cylinder. Junk can be either lean or rich because the junk disturbes the spray pattern....neither condition will necessarily set a "code" (DTC) because the injectors are monitored indirectly by the ECM...via the O2 sensors mostly. The thing is if your miss is real & only at or just off idle speed then I would ask if it gets worse as the car gets to proper coolant temp? It's kind of okay when stone cold? It's there when cold but gets worse as she warms up? All those point to injector coil shorting....in that scenario the injector's short will get worse the more heat gets to the coil and that's the give-away to shorted coils, the miss doesn't go away rather it gets worse. If it is injectors it will get much worse as time passes...the miss that is. I would also do some looking at all your vacuum connections and pull the plugs for inspection, oh and do a spark test while you're there. The more you can eliminate in the absence of a scan tool the further all of us might have some ideas to pass along. The scan makes it easy but diagnostics can be done without one....it's just back to basics. Ya know does it smell rich or lean, the fuel filter is new, the PCV's are good, the vac connections are all in place & there is no sucking noises, Your vac gauge says it's not lean or rich. You get the idea, right? Oh, yea the spark test will help you eliminate the wires and coils...ya know pull one at a time when shes at idle? Sorry to be so long winded about this! Good luck & post up! Tom __________________ 1990 ZR-1, Black/grey, #2233, stock. ZR-1 Net Reg Founding Member #316 & NCM member Last edited by tomtom72; 03-01-2007 at 06:45 AM.