Tim240z Posted April 4, 2004 Share Posted April 4, 2004 Here's the thing. I have replaced just about every component of the ignition system on the LT1 in the Z, so I can only now summize that the problem is with the injectors (off idle stumbling when warm). So here is the question: What is the likelyhood that one or more of the injectors are mechanically damaged/worn out as opposed to being maybe just 'dirty'? When I first fired the engine after the conversion, a few (maybe 3) of the injectors weren't firing, but a couple of taps on teh injectors with a wrench freed them up. Do I take the injectors in to get tested/cleaned etc, or should I rather put that $$ towards a set of brand new injectors. What I concerned about is that if/when I get the injectors tested, I will need to replace some of them (in which case I would replace all of them). Or is it more likely that the injectors are just gummed up, not worn out, in which case the less expensive alternative would be to just clean them. And.....if I do replace the injectors, which ones are recommended? How about the Accell injectors, 30lb/hr: High performance, 30 lb./hr. injectors These 30 lb. per hour fuel injectors feature a Bosch style pintle design for increased fuel atomization. Other features include an anti-plugging vapor cap, a low mass internal needle valve, and a pressure spring for faster response time. Tim Quote Link to comment Share on other sites More sharing options...
DaleMX Posted April 5, 2004 Share Posted April 5, 2004 From what I understand, upgrading the injectors should not be a problem as long as you tune for it. If you dont then the increased fuel will make you run so rich that it will fuel wash the cylinders (destroy the rings). Also the lb per hour is dependant on the the fuel pressure. The 30 lb ford injectors I installed on my LS1 are actually 36 lb at 58 lbs. If Im not mistaken your running an LT1. Best advice would be to find a good LT shop and get them to do the upgrade and tuning on a wideband. This is a usefull LT1 forum http://www.ls1tech.com/forums/forumdisplay.php?f=31 Dale Quote Link to comment Share on other sites More sharing options...
Afshin Posted April 5, 2004 Share Posted April 5, 2004 I believe that most often injectors are dirty and can be cleaned/blueprinted (unless it was a recalled injector or really cheap ones). There is this company that apparently does great injector servicing rivaling RC engineering, however, they charge $11 per injector as opposed to $28. ( I got this info from the Mach IV/supra twin turbo guys). The process is explained on their website. For all you know, your injectors might not be bad. Here is the link: http://www.cruzinperformance.com/fuelinj.html Quote Link to comment Share on other sites More sharing options...
Owen Posted April 5, 2004 Share Posted April 5, 2004 Make sure you get the ones with the right impedance, either high or low. OEM style injectors were high impedance (I think) and I needed low. The ones I saw in summit or jegs weren't usable with my EFI system. Owen Quote Link to comment Share on other sites More sharing options...
cdk4219 Posted April 6, 2004 Share Posted April 6, 2004 Typically the off idle stumble doesnt follow the patterm of an injector problem. I am not familiar with the LT1, but upping the size of the injector on a stock or near stock engine probably wont get you much, but lighter in your pocket. Re sizing injector tables is needed for the ecm to find the proper pulse width. Injectors can be checked and cleaned by local shops that specialize in this, and the cost isnt great. Have you read the real time data from your diagnostic tool? many times this will point you in the right direction. Injectors wont usually wear out all ath the same time, and many times it is the coil that wears out rendering the unit totally useless. that's not to say that it cant happen, but it is highly unlikely that all of the injectors need to be replaced. With that being said a bad injector would show up on one or more cylinders when it ran them lean, or rich which in turn would usually lead to a hard start problem when the injector leaked into the cylinder. I would suspect the problem related with a possible vacuum leak, or TPS, but not the injectors, but I have been wrong before. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted April 6, 2004 Author Share Posted April 6, 2004 Well, while I agree with you on the increases injector size,...if I'm going to buy new injectors, I might as well go slightly larger to keep up with future upgrades. The fact that it starts when the injectors are warm, I'm thinking that one or more of them are increase the resistance in their coils, since they are old and have sat for so long. What does make me curious is that it clears up AS SOON as the gearbox is popped into neutral. As soon as it goes back into first (or second) it stumbles again...just like it's dropped a couple of cylinders. I checked the resistance through all the injectors with an ohm meter and get mainly 12.2, but 12.0 and 12.1 on others. This seems ok, butr then again it's with the injectors cold and unplugged with no current flowing through them..... I'm at a loss..... I check the current of the TPS and compare to the FSM and check the resistance on the engine temp sender. Tim Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 6, 2004 Share Posted April 6, 2004 What plugs and wires are you using? When my LT1 was stock, I had original plug wires, and ACdelco platinum plugs(stock replacements). I developed a wicked miss at high RPM that went away when revved in neutral. But it wouldn't rev passed 4500 when in gear. I replaced the plugs, wires and coil at the same time(Bosch plat +4's, MSD wires and coil), and it was the best money I had spent on it since I had bought it. Throttle response improved dramatically. With the major mods done to the engine now, I have Taylor wires and NGK TR55 non-platinum plugs. From my experiance, the only plugs that show up on parts stores systems are the plat replacements. Only local place I could find the NGK's was BAP/Geon. Apparently, the plat tips can come off and open the gap up too wide on the plug. I just replaced the ECU in my car and man what a differance. I was running the stock tuned ECU on my heads/cam built LT1. My "new" ecu is tuned for the ported/polished heads, HOT cam kit, and various other obvious tuning, plus VATS delet, and no MAF. My already rev happy LT1 now screams thru the RPM's, damn I can't wait to have that motor in my 240. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted April 6, 2004 Author Share Posted April 6, 2004 Jamie, I'm running MSD 8.5mm wires and new plugs (Champion). I have TunerCat, so PCM access is not an issue. Tim Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 6, 2004 Share Posted April 6, 2004 Carbon build up on the throttle blade? My Lt-1 get build up on the blade and needs to be cleaned or it runs rough at low RPMs Quote Link to comment Share on other sites More sharing options...
Tim240z Posted April 6, 2004 Author Share Posted April 6, 2004 I just had the intake off and the TB off the intake. I cleaned it extensively with TB cleaner (aerosol), so I don't think that's it. It was pretty dirty though, but more just dirt than carbon. I also double and tripple checked all the possible areas for vacuum leaks. I think the injectors are just old and are 'breaking' down when the coils get warm...... Tim Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 6, 2004 Share Posted April 6, 2004 Tim, did you remove the IAC and clean that seperately? It gets ALOT of build-up down inside it. Even if you sprayed the cleaner into the hole that leads to the IAC, it can still be clogged. I promise we can figure this problem out. FWIW, my LT1 is pretty well modified, has ORIGINAL injectors that have never been sent out for cleaning, etc..., and has no stumbles. I have had some stumbles in the past, but they always went away with maintenence. Fuel filter is an overlooked culprit of off idle stumbles. Voltage to the pump? Is this on your Z28 or the 'Goose? Maybe some BG fuel system cleaner through a tank of gas. It couldn't hurt to get some new injectors anyway. I'm not going to spend that money until I need to though. I don't chase problems by replacing parts. I can't really afford to. Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted April 6, 2004 Share Posted April 6, 2004 Did you check the range voltage on all your sensors? I'm thinking the temp sensor that checks the temp of your coolant. Since weird things are happening when hot, maybe the temp sensor is out of wack? Quote Link to comment Share on other sites More sharing options...
Tim240z Posted April 6, 2004 Author Share Posted April 6, 2004 Well, depending on the schedule for getting the car to the hospital (aka bodyshop), I will test the following as recommended by the FSM: TPS (although I doubt it as it would likely cause the problem all the time, even when cold) The Temp sensor....this one has always been in the back of my mind, but when running with FreeScan hooked up, the PCM is showing a temp reading very close to the gauge (seperate senders), so I'm thinking that one is OK. Jamie, I did not remove the IAC, but I pretty much soaked the whole unit. It's easy enough to remove again, so I may do that. I'm still 'convinced' that a couple of the injectors may be bad, considering the history (97k+ miles on them, plus I had to 'tap' them free on initial startup). I might pull off the fuel rail/injectors, and swap it out with the Z28 and see if I get the same problems with the Camaro.... Tim Quote Link to comment Share on other sites More sharing options...
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