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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I have a cold engine, less throttle problem on my 91 V6 F-body
The case: when the engine is cold, and I step on the gas, i don't get any throttle.
Background info
Engine starts 99% everytime, right away. The idle speed is a little bit wobly but all 6 cylinders are running. I changed Rotor, dist.cap spark cables and plugs, airfilter. That did some good. I.e I had a fuelsmell due to imcomplete combustion, that's gone. When the engine got warm, the engine would start to stutter and fall out. That's also gone. In essence now: the warmer the engine gets, the better the throttle.
Today I tested the car after the tune up and when the engine got warmer, the engine would run smooth on idle, when punshing the gas pedal, instant thrust.
So the car has been standing still for three years.
And there's something else: the prev. Owner changed the injectors. The old once, 3 of theme were damaged, 3 are cleaned. But because injectors for a F-body are hard to get here in the netherlands, he placed 3.4 injectors on the 3.1 engine. I have the refurb. Injectors from southbay and waiting on gasket set, but i will change these. My assumption is that the engine gets to much gas?
And i have check the odb for errorcodes, nothing
Well, thats all the Info i have so far. Hope somebody can get me on the right track
Cheers
Don
Ps. I have added an image of my ign. Coil?before i changed the dis. Cap. What do you guys think of that?
Last edited by Donald Croes; 04-09-2016 at 11:28 AM.
I have a cold engine, less throttle problem on my 91 V6 F-body
The case: when the engine is cold, and I step on the gas, i don't get any throttle.
Background info
Engine starts 99% everytime, right away. The idle speed is a little bit wobly but all 6 cylinders are running. I changed Rotor, dist.cap spark cables and plugs, airfilter. That did some good. I.e I had a fuelsmell due to imcomplete combustion, that's gone. When the engine got warm, the engine would start to stutter and fall out. That's also gone. In essence now: the warmer the engine gets, the better the throttle.
Today I tested the car after the tune up and when the engine got warmer, the engine would run smooth on idle, when punshing the gas pedal, instant thrust.
So the car has been standing still for three years.
And there's something else: the prev. Owner changed the injectors. The old once, 3 of theme were damaged, 3 are cleaned. But because injectors for a F-body are hard to get here in the netherlands, he placed 3.4 injectors on the 3.1 engine. I have the refurb. Injectors from southbay and waiting on gasket set, but i will change these. My assumption is that the engine gets to much gas?
And i have check the odb for errorcodes, nothing
Well, thats all the Info i have so far. Hope somebody can get me on the right track
Cheers
Don
Ps. I have added an image of my ign. Coil?before i changed the dis. Cap. What do you guys think of that?
Little update:
I disconnected my MAP sensor and fired up my engine to see if that would make a difference. No results. Cleanded it and filled up my gastank
My 2 dollars are still in on the wrong injectors. Can imagine that the engine gets to much gas and the system has hard time compensating
o2 sensor could be faulty even though it isnt throwing any codes. could have a lot of carbon build up on it, making it not read correctly and leaning out or enriching the system too much. just a thought.
Are you road testing the car? Is it actually accelerating normally while driving when warm?
The O2 sensor affects closed loop operation and can prevent the engine from achieving closed loop. However, a normal running system doesn't achieve closed loop for atleast 30 to 60 seconds after engine start. Longer on systems with single wire(unheated) O2 sensors. That doesn't explain your symptom right after engine start. I have seen rare cases where a shorted sensor caused a system to over-fuel. An issue like this doesn't improve with the engine warmed up. Also, if the O2 sensor was faulty you would most certainly have a fault code stored as even on the early systems there were fault codes for sensor high or low. O2 sensor codes will set even with no symptoms noted.
Injector failures almost always show up first when hot. If your engine runs normally when warm, it is unlikely that the fault is with the injectors. I do have faith in Southbay and if the injectors in the engine now aren't correct for the application, you are wise to change them. I just don't expect it to solve your immediate problem.
As the symptom seems to change with engine temp, my first thought would be the engine coolant temp sensor. I don't mean the single wire gauge sender in the cylinder head, but the two wire sensor mounted below the thermostat, at the front of the engine. This sensor informs the ECM of engine coolant temperature. The ECM's fuel delivery rate changes dramatically with engine temperature. A cold engine needs much more fuel to operate than a warm engine. Check the connector terminals for oxidization.
If you have an ohmmeter you can test the sensor for resistance. It should read about 3,500 ohms at 70 degrees and 180 ohms at 210 degrees. Better yet, if you can find a capable scan tool, you can view ECM data, including engine coolant temp to verify if it is correct for the actual temp of the engine.
If the sensor is reporting coolant temperature much warmer than actual when the engine is cold, you will have the very symptom you have now. I have seen this type of in range failure a few times.
Thanks for tagging along and your input
Road testing
YES! the car accelerates normal when the engine is warm
02 Sensor
I haven’t got a OBD scanner, but dit the “Paperclip” trick and there where no error codes
I have seen a way or two to check if an 02 sensor is faulty. Can you help with that?
It was also with an Ohm meter, right?
Injectors
They aren’t failing actually, there are to big
It’s a 3.1 V6 engine, but the current injectors are 3.4 injectors. The previous owner swapped the faulty 3.1’s for 3.4
The injectors are working properly, but my thoughts on this is that the ECU is programmed for 3.1. injectors and it can’t manage the flow properly. fyi: the 3.4 injectors are from a F-body 93 and up. I have asked my local US car garage and he checked the specs of the 3.4;s and he confirmed that these 3.4 will not work fine because the flow is different then the 3.1’s. Simply said: the engine is getting to much fuel because there are to big.
Some weeks ago, I contacted SouthBay already and Julie has send me a set of 3.1 Bosch Injectors.
Engine Coolant Sensor
Great and good pointer. I’ll check he connector and clean it
I have got an ohm meter at my dads and will test it
Question on how-to: where do I place the (black) Ground? and where do I place the Red one?
One on the body of the meter, other on one of the pins?
And I assume (to be shure) that the motor must be up & running
Thanks Doc!
Will report back asap
cheers
Last edited by Donald Croes; 04-15-2016 at 07:00 AM.
Well, I it wasn't the CTS, it is the connector, I think. I tested the connector. It should be around 5V. No matter what I did, i would have no reading or the Voltage would jump around. Tested also for continuity, no signal what so ever. (Yes The multimeter is working)
So, i want to check if there's a shortage in the wires. I'm I correct that I have to remove the plenum to get to the PCM? Or is there an easier way? Would be great if the wires are faulty that I can replace without tearing all kinds of parts out
Test the ECT sensor for resistance between the two pins. It is not grounded to the body. Test it with the engine off. The engine should not be run with the sensor disconnected. With key on engine off, you should 5 volts between the yellow and black wires. If not, then verify ground on the black wire by testing for voltage from the wire to batt+. Test for 5V from the yellow wire to a good engine ground.
Be aware that your tester leads may be too large to contact the terminals of the sensor connectors. Never try to push the test leads into the terminals or you will destroy them. If you are sure that there is not 5V on the yellow wire and a good ground on the black wire, you may have to access the ECM for testing. Be very careful there not to short any circuits. Never test for resistance on any connected ECM circuit.
Resistance is not a valid method for testing the O2 sensor, except for the heater circuit on a heated sensor. Your car has a single wire sensor so ohm testing is out. You can test the O2 circuit from the ECM for .450mV with the sensor disconnected. Then, with the engine running and warm, you can test for toggling voltage from 200 - 800mV on the signal wire. If the voltage doesn't toggle, try running the engine at 2,000 rpm for several seconds to heat the sensor up. The single wire sensor has to be heated by exhaust to operate. In order to perform voltage tests on this system you need a voltmeter with 10Megaohms per volt input impedance. The cheap meters you buy at Harbor Freight won't work. The ECM circuits have internal diagnostic resistors on them. In order to accurately measure voltage through these resistors, a voltmeter must have much higher internal resistance. That's why we can only use 10Megaohm voltmeters.
If you aren't sure about the one you have, read the owner's manual or visit the manufacturer's website, or just buy a Fluke DVOM.
If by OBD scanner you mean OBDII, those scanners won't work on your 91.
Okido, to give a thorough update, I checked my ETC sensor by taking it out amazing and test in open air and secondly with a thermomoter and hot water. The sensor works. Hands down!
Measuring voltage on the connector: I didn't start the engine but i did turn the ignition on. Imho I do need electricty right? The car isn't running, just turned the key to 'accesory mode'. I placed my ground on blank peace of metal, a bolt and scraped it a little to find a ground and after that placed the ground on - of the battery. Placed a small red pin on the yellow...I tried these three options with the ground. I had really bouncy readings, or I had nothing or it would show 1,5 Volt and slowly build up to 2V. That's weird, right? I tested for continuity bij placing ground and red on the connector and there was no response at all. Double checked it by asking a mate to verify and he confirmed, no readings at all...i'm almost positive i made a connection with my connectors
So I would like to check the cabel of there is something wrong. As you mentioned, check the ecm...what i assume is the right way is taking of the cable and check it for brakes and cracks in de cable with my multimeter. I am new bee at this car, so as mentioned, do I need to take of intakeplenum to get to the end of ETC pigtail? Or is there an easier way to get there?
Fyi: the pigtail goes in under the intakeplenum, and there it 'magiclly' disappears!
02 sensor, great and thanks!
I ment ODB 1, i am aware that ODB2 is an other protocol
The ECM isn't turned on in accessory position of the ign switch. Have to have the key in run position, engine not running. This is key on engine off or KOEO. You know you're in the right spot when your warning indicator lights come on. You can test the circuits two ways, for voltage or for continuity. For the voltage test, you would leave the ECM connected and gently, carefully back probe the yellow wire looking for 5V with the ECT sensor disconnected. The yellow wire is the ECT signal. The ECM provides a 5V base on the signal circuit. The ECT, which is negative coefficient thermistor reduces the 5V according to temperature. The result is the ECT signal.
To test for continuity, you would disconnect the ECM and the ECT sensor. Test each of the ECT sensor circuits for continuity from end to end. Then test for shorts to ground or power or any other circuit in the ECM harness. I prefer the voltage test method.
If your DVOM is of low input resistance, you will not see 5V on the ECT signal circuit, even with the sensor unplugged. The current through your meter will drop voltage. I've had this happen even with a 10Mohm voltmeter on circuits where the diag. resistor value was high.
Well, I started this evening on removing the plenum as I needed to change the injectors. I checked where my ECT sensor's pigtail went as it disappeard in a cabletube with other cables under the plenum. Followd the cables and what do you know...the sensors pigtail goes up and after few inches is folded back really in sharp cornerand goes back to a multi-connector which I assume is the PCM?
Seeing how sharp the cable is twisted back I really starting to believe that the cables are damaged.
I already have a spare pigtail, so does anybody have a tip on how to remove the old cable from the pcm and place in the new one.
Ah, our messages have crossed each other! Thank you for the explination. One question regarding checking the voltage.
As A dutch guy, there are some words/terms i have to guess, what do you mean with 'back probe'
Accesoire mode, I always thought that was the name for when you turn your key and the dashlights come on. But to make things clear, it's in Run position when I check for voltage
Got it and Fixed My first idea was almost spot on: faulty injectors!
Today I changed the 3.4 injectors to 3.1 which I got from Southbay. While taking out the injectors, i saw that also some o-rings weren't replaced (had cracks). Swapped the injectors, cranked up the car and bam! It runs Wonderfull!
Thanks doc for all the intel, learned a lot from it
Cheers
D
Last edited by Donald Croes; 04-29-2016 at 02:16 AM.
04-09-2016, 11:23 AM
