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So I have a fuel injector that is intermittent. The car misses out at idle on 1 cylinder.
I have changed fuel injectors, injector plugs and checked grounds. I have tried a noid light. Once the noid light is plugged in it doesnt start flashing until about 5 seconds after starting.
I also have some strange readings on the o2 sensors. when it was warmed up I had readings on bank 1 about .450 but on bank 2 anywhere from .950 to 1.05. My understanding is that this should have nothing to do with the injector problem since the ecm is only checking for electrical problems.
My question is what should I check next? (I want this thing out of my garage :0 )
Have you checked the resistance of the fuel injector? Low resistance can set DTC 18, or even cause the fuse to blow. When the DTC sets, the PCM shuts down the injector driver causing the misfire. If resistance is marginal, it may cause an intermittent fault. The lower limit for resistance, according to the DTC 18 flow chart in the factory service manual is 11.6 ohms, and when measuring the injector resistance, coolant temperature should be near 70-degF.
Do you have 12 volts at the pink wire in the injector connector, key on?
An O2 sensor that is stuck at 450mV may be faulty. The PCM supplies 450mV as a reference voltage. If the sensor is faulty, or not warmed up, the reading will remain at 450mV. Rich mixtures (950 - 1050mV) can be due to cold start enrichment. Voltage in open loop should drop as engine warms up. And when the sensors warm up the PCM should switch to closed loop, ,and the voltage readings should start to cycle rapidly between 100-900mV.
Free download of 1994 factory service manual, courtesy of GaryDoug:
I have checked all the resistances and the voltages on the fuel injector connectors they range from 11.9-12.1.
The reason I ask about the o2 sensors is because i didnt know if they could cause a fault in the injectors? 1 bank was running a steady .900-1 after being warmed up. Another thing i did try was another ecm i had handy and it did the same thing.
Last thing to check i guess is the wire to the ecm but i did move it around while it was running and cant seem to get it to vary the missing.
Today i was going to change the o2 sensor and the passenger side and cant get it off. I am seriously considering pulling the motor. I will probably swap it out with another 1 i have here.
Would a high knock count cause any injector issues?
As you have already pointed out, DTC 18 is set by voltage on the injector circuit not being within spec.
The O2 sensors should not cause the PCM to set the DTC 18 code. On the other hand, if the O2 sensors are staying relatively static even when the engine is warmed up, something is preventing the PCM from going into closed loop. The sensors have to reach 600°F to read correctly, the coolant has to reach a minimum temperature which is usually about 140°F, and a timer from cold start, usually 206-seconds has to time out. A more logical question would be whether the DTC 18 prevents the PCM from entering closed loop, and I don’t know the answer to that one.
The sensors are usually easier to get out if the exhaust is hot.
finally got the o2 sensors replaced and still getting the same readings. Bank 1 is like .100 and bank 2 hovers around 800-900. When i wot the car burns tires ect, seems the miss goes away. Just idling the car has a definite miss. Pulled #7 injector and the miss goes away. I assume it is running on 7 cylinders. I guess my next step will be to pull all the wires out of the plastic protective sleeve and trace #7 down to the ecm and see if i get continuity ? This would be my only guess.
One last question, could this be mechanical? Stuck valve?
And the O2 sensors are somewhat static at those readings? When exactly are you seeing those numbers - cold start, part way through warmup, at least 5 minutes after cold start, normal driving, full throttle? What are you using to read the sensors? You can't just take a single freeze frame of data. You have to watch them over a period of time. What LTFT cell is the PCM operating in when you see those numbers?
Don't tear the harness apart. Use a noid light. If it flashes the wire from the PCM to the injector is OK. The PCM is supplying a ground to fire the injector l
i took that reading at about 180 degrees (o2 sensor) . They do fluctuate but generally stay in that zone at idle. I havent really taken it out for awhile driving so dont know what the readings will be. I am using 94/95 scan to get the info. I havent learned to use tunerproht yet. It will connect but i am not sure how to get it to scan where i can see variables. My fuel pressure is about 45lbs at start and bleeds off very slowly. I dont recall what it is while running i would have to hook it back up.
Oh and another thing, I am getting a (what i consider) a high know count. Over the course of 20mins of idling in the garage i had over 2k knock counts. I think there is an exhaust leak on the passenger side. I would like to bypass it.
I might also add that this car sat for about 10 years in a garage.
Knock count normally increases during startup. It isn’t necessarily knock. And it is an “incrementing” field. If it was 2,000 when you turned off the engine, that's where it will read when you turn the key to start. The number is not important by itself, it's how fast the number is increasing. And when it reaches the maximum possible number, constrained by a 16-bit field, it resets to “0” and starts increasing all over again.
More important is whether there is any knock retard shown in the log. If there's no knock retard, the increasing knock count is not affecting anything.
Still no solution to this problem. Only thing left (i think) is to trace wires in wiring harness and check those.
i have attached a scan using scan 94/95 if its any help. about 1/2 way through the scan i went for a drive got up to about 4k rpm but roads are wet, went sidewayz
Well found the problem. I tore into the wiring harness and found at the back of the block that the a number of fuel injection wires were melted so i cut the bad and put in shrink butt connectors.
But now i have a new problem, the car just backfires like crazy on acceleration. I am guessing stuck valve.
I have no trouble codes.
Well the wire was the same diameter and same color.. Was red and black which on mine is the #7 fuel injector. The other wire that was burned up was a blue (and something) wire. It was in the same bundle and was the same diameter wire. It was located on the passenger side, by the fire wall. It was an offshoot of the large bundle.
In the pic of the harness it would be right below where it is labeled hvac vacuum in that foil protectant.
I appreciate the help.
Now i gotta figure out why it is backfire out the exhaust on acceleration. Like really bad.
I took off the passenger side valve cover. Nothing of note that i saw. Will do the drivers side here in acouple weeks try to find the problem.
I will be adjusting the lifters. Its been a long time since i have done it so i wanted to watch a video as a reminder of how to do it.
Found the problem, when I replaced the opti.i switched 5 and 7. Runs good now.
Lol I feel stupid. Just goes to show check the simple things 1st.
thx for the help.
Next project putting 383 lt1 6 speed in 87 olds cutlass
