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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / December 2005Fuel Injectors cross wired
After replacing the heads, I may have miswired the fuel injectors on a '94 Oldsmobile Cutlass - 3100 SFI V6. I may have switched the front cylinders 2,4,6 with the rear 1,3,5. The firing order is 1,2,3,4,5,6. The car runs but not very well. Is it possible for a car to run with the wires switched? Otherwise, I have a different problem. > After replacing the heads, I may have miswired the fuel injectors on a > '94 Oldsmobile Cutlass - 3100 SFI V6. I may have switched the front > cylinders 2,4,6 with the rear 1,3,5. The firing order is 1,2,3,4,5,6. > The car runs but not very well. Is it possible for a car to run with > the wires switched? Otherwise, I have a different problem. Its quite possible for a port fuel injected engine to run with the injectors miswired. The fuel just sits there on top of the intake valve until the valve opens. Atomization isn't as good, efficiency will no doubt suffer, but it will RUN. In fact early port efi engines (and some current ones when cold) run in "batch-fire" mode where all the injectors fire a little bit on every cylinder firing, rather than firing one big slug timed with the individual intake valve. I agree with Steve, the fuel can't do nothing but set there till the valve opens. The AZ site should have a wiring diagram on your vehicle, you can check the injector wiring colors, just to double check. Thanks to all for the great information. Ok, so I started removing the bolts on the plenum, thinking that I had indeed miswired the injectors....when I noticed a loose spark plug cable on cylinder # 2. I recall having dropped a spark plug that I then had to regap. Apparently when I dropped the plug it cracked the porcelain as well as the conductor inside the plug so that one cylinder was not firing and what was left of the plug in the wire was arcing. I fixed that problem with one of the old spark plugs and it ran like a champ. BUT.....I smelled some gas in the engine compartment. At least two of the fuel injectors are leaking, possibly at the fitting with the intake manifold. I replaced the o-rings on the rail but not the ones on the intake manifold. As hard as I tried, I could not pop out the injectors. (The Haynes manual said to lift the rail straight up along with the injectors. No way that was going to work.) Yesterday on AZ I saw how you can use two screwdrivers (one as a fulcrum) to pop out the fuel injector. QUESTION - Is there any way to tell if the leaks are occurring at the rail or at the intake manifold, or do I just replace all of the injector-manifold o-rings and hope the problem is rectified? In fact early port efi engines (and some > current ones when cold) run in "batch-fire" mode where all the injectors > fire a little bit on every cylinder firing, rather than firing one big > slug timed with the individual intake valve. That's interesting info, Steve. Is this basically a domestic maker strategy? Are there specific engine families that you can site? I have not heard of this done on any Asian vehicles. Of course they almost all waited until OBDII was enforced before going to SFI on any of their models. Hell, many '95-back wiring diagrams I've seen show the entire set of injectors grouped as one on my beloved rice burners, but their economy was still typically pretty decent... Toyota MDT in MO > In fact early port efi engines (and some > [quoted text clipped - 4 lines] > That's interesting info, Steve. Is this basically a domestic maker > strategy? No, it was an early/simple EFI strategy. Basically just a baby-step from throttle-body injection toward sequential multi-port EFI. Also quite a number of cars with sequential multi-port injection did (probably still do) operate batch-fire when the engine is below a threshhold temperature because extra enrichment can be provided regardless of throttle opening and RPM that way. >Are there specific engine families that you can site? GM did it a lot because they went EFI across the board so early compared to most other automakers, who stuck to feedback carbs for many applications a lot longer and then tended to jump straight to true sequential port EFI. I occasionally see references to certain 1980s versions of the Buick 3800 as being batch-fire port EFI, and thus being an really easy system to retrofit to almost any old similar-displacement six-cylinder engine because the controller doesn't need to know cam position. Bosch L-Jetronic from the mid-80s used a injectors in parallel: BMW, Volvo, Saab, etc. > In fact early port efi engines (and some > current ones when cold) run in "batch-fire" mode where all the injectors > fire a little bit on every cylinder firing, rather than firing one big > slug timed with the individual intake valve. BTW, my last question was centered around the statement "and some current ones when cold". Obviously the old port injected models were grouped, by definition. Toyota MDT in MO In article <1133805118.499830.7980@o13g2000cwo.googlegroups.com>, > After replacing the heads, I may have miswired the fuel injectors on a > '94 Oldsmobile Cutlass - 3100 SFI V6. I may have switched the front > cylinders 2,4,6 with the rear 1,3,5. The firing order is 1,2,3,4,5,6. > The car runs but not very well. Is it possible for a car to run with > the wires switched? Otherwise, I have a different problem. The "S" in 3100 SFI V6 stands for sequential. Yes, the engine will start and run, but it won't run properly. The injector harness is labeled for which cylinder, the lower intake is marked for cylinder also, but you have to look at where the respective injectors point to... things aren't as they seem when viewed casually. > In article > <1133805118.499830.7980@o13g2000cwo.googlegroups.com>, [quoted text clipped - 12 lines] > the respective injectors point to... things aren't as they seem > when viewed casually. I wouldn't think it would make THAT much difference... tons of VWs are out there running CIS quite happily... nate  Signaturereplace "fly" with "com" to reply. http://home.comcast.net/~njnagel > > The "S" in 3100 SFI V6 stands for sequential. > > Yes, the engine will start and run, but it won't run properly. [quoted text clipped - 6 lines] > I wouldn't think it would make THAT much difference... tons of VWs are > out there running CIS quite happily... Ah, but it does. Two well known- well respected contract trainers use this exact scenario in their class(s) based upon a vehicle that made the rounds to a number of Chicago area repair shops (dealer included). IIRC, it was a dealership that f.cked it up to begin with... Those trainers are; John Thornton Scott Manna Using the proper wobble extension, it's not even necessary to remove the fuel rail (and thusly the injector harness) when removing the lower intake on a 3100 as part of a cylinder head repair. >>>After replacing the heads, I may have miswired the fuel injectors on a >>>'94 Oldsmobile Cutlass - 3100 SFI V6. I may have switched the front [quoted text clipped - 10 lines] > I wouldn't think it would make THAT much difference... tons of VWs are > out there running CIS quite happily... One problem with a V engine is that they normally use two oxygen sensors, and swapping the injector harness to the wrong bank will make the ECU compensate on the wrong bank, which likely will make the engine run like crap. > nate Thomas > >>>After replacing the heads, I may have miswired the fuel injectors on a > >>>'94 Oldsmobile Cutlass - 3100 SFI V6. I may have switched the front [quoted text clipped - 15 lines] > the ECU compensate on the wrong bank, which likely will make the > engine run like crap. Ah... that makes more sense now, I wasn't thinking of it like that. Obviously a VW engine is an inline engine so there's no issues like that - one O2 sensor, one adjustment. nate > One problem with a V engine is that they normally use two oxygen > sensors, and swapping the injector harness to the wrong bank will make > the ECU compensate on the wrong bank, which likely will make the > engine run like crap. Its a Chevy 3100. Running like crap is part of the design ;-p Maybe I miss-read the wiring diagram, but it only showed 1 02 sensor. So how would the computor know which bank is rich or lean? I believe the vehicle is still OBD1, so no miss-fire monitor. thanks > Maybe I miss-read the wiring diagram, but it only showed 1 02 sensor. So > how would the computor know which bank is rich or lean? I believe the > vehicle is still OBD1, so no miss-fire monitor. thanks I think that the comment was made in terms of it being a POSSIBLE effect in V-type engines in general. I do know that some V-type engines do independently monitor each bank's exhaust AND have a separate knock sensors for each bank and can selectively alter timing on individual cylinders. Thanks to all for the great information. Ok, so I started removing the bolts on the plenum, thinking that I had indeed miswired the injectors....when I noticed a loose spark plug cable on cylinder # 2. I recall having dropped a spark plug that I then had to regap. Apparently when I dropped the plug it cracked the porcelain as well as the conductor inside the plug so that one cylinder was not firing and what was left of the plug in the wire was arcing. I fixed that problem with one of the old spark plugs and it ran like a champ. BUT.....I smelled some gas in the engine compartment. At least two of the fuel injectors are leaking, possibly at the fitting with the intake manifold. I replaced the o-rings on the rail but not the ones on the intake manifold. As hard as I tried, I could not pop out the injectors. (The Haynes manual said to lift the rail straight up along with the injectors. No way that was going to work.) Yesterday on AZ I saw how you can use two screwdrivers (one as a fulcrum) to pop out the fuel injector. QUESTION - Is there any way to tell if the leaks are occurring at the rail or at the intake manifold, or do I just replace all of the injector-manifold o-rings and hope the problem is rectified? I understand the talk about the number of 02 sensors was general. Talking about the vehicle in question, I don't think the computor can tell which bank is rich or lean. So if the injector timing was off, why does the vehicle run badly? If the fuel charge just sits there till the intake valve opens, how is that different than mfi? I'm not saying SFI isn't better, I'm sure it is, but why would the vehicle run rough? thanks |
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