1998 Chimaera 450 Misfire after minor job
Discussion
Ive not read all the posts but here are the basics on a rich mixture.
Both banks over fuelling- AFM. - voltage output too high - check it with no airflow- should be around .3 to .34 volts . This is important if its higher all the AFM output will be wrong across the whole range. Another point is the CO trim voltage stuck high. Check the CO trim as per the G33 web page- it should be possible to change the engine note winding the voltage up and down as it goes rich or lean just like adjusting a carb idle mixture. Low voltage lean, high rich. The CO trim is a 5 k resistor to ground that pulls the ECU supplied 5v down to the trim voltage. If its open circuit you get 5v at the ECU and highly over fuelling. Trim voltage is normally between 1.4 and 1.8 volts. Also make sure the AFM plug / cable are not damaged.
Temp sensors- you have checked them but you can double check with a cold engine when both fuel rail and water temp should be near the same as the devices are electrically the same.
Fuel pressure too high. Lost vacuum to the regulator or blocked fuel return pipe
Stuck injectors- only happens on one bank at a time if the injector loom shorts to ground and opens the injectors constantly.
Just a note on "common" grounds. The AFM has a dedicated ground wire back to the ECU as does the TPS as small signals going back through the engine ground plane could be altered by stray ground voltages. Sensors must be measured on there own ground wires and not the engine block.
Both banks over fuelling- AFM. - voltage output too high - check it with no airflow- should be around .3 to .34 volts . This is important if its higher all the AFM output will be wrong across the whole range. Another point is the CO trim voltage stuck high. Check the CO trim as per the G33 web page- it should be possible to change the engine note winding the voltage up and down as it goes rich or lean just like adjusting a carb idle mixture. Low voltage lean, high rich. The CO trim is a 5 k resistor to ground that pulls the ECU supplied 5v down to the trim voltage. If its open circuit you get 5v at the ECU and highly over fuelling. Trim voltage is normally between 1.4 and 1.8 volts. Also make sure the AFM plug / cable are not damaged.
Temp sensors- you have checked them but you can double check with a cold engine when both fuel rail and water temp should be near the same as the devices are electrically the same.
Fuel pressure too high. Lost vacuum to the regulator or blocked fuel return pipe
Stuck injectors- only happens on one bank at a time if the injector loom shorts to ground and opens the injectors constantly.
Just a note on "common" grounds. The AFM has a dedicated ground wire back to the ECU as does the TPS as small signals going back through the engine ground plane could be altered by stray ground voltages. Sensors must be measured on there own ground wires and not the engine block.
Edited by blitzracing on Tuesday 11th April 17:10
Edited by blitzracing on Tuesday 11th April 17:26
Hi Guys, I cant believe my car has been off the road for such a long time. Mostly though I've not been working on the car because on my trip home to the UK in May/June this year. Following that, I lost a dear friend Jim Gamsby who may be well known to many of you as the NZ TVR Guru. Jim lost his fight with Cancer and will be very much missed by the local NZ TVR community.
I started going through everything again with fresh eyes about a week or so ago. Here are my findings.
The ECU Wiring has been checked. I had an old wiring loom (From a Griff) that I used to confirm some things that I couldn't physically check. These are shown here;
Of Note and compared to the wiring provided by Steve_D, I don't think the Black/Red wire that connects the AFM and other sensors is directly connected to earth. Instead they all connect at the loop back connector and I assume earth return is via the ECU. Also, the Orange/Brown wire that provides 12V to the AFM via the main power relay is linked in the relay, so removing the relay from the socket separates the two lines so that they can be tested independently.
The advice to remove each sensor, Injector etc. was fantastic. I have now tested every wire for continuity, shorts against the battery +Ve and -Ve and every other pin on the ECU. There are no issues and this also proved how the lop back connector has grouped the wires.
Unfortunately though, I have still not found the issue. In addition to the wiring checks, I have
Put the old ignition coil back in
Changed the plugs back to the original and installed the spark plug shrouds
Checked all tests listed in the 14CUX manual (actually I haven't checked everything - but have all the ones I think needed to be)
Checked voltage and resistance across everything I can check.
The results generally within spec except the AFM. I have two AFM's that were both okay before I did any work on the car. Both test exactly the same.
Signal (Blue/Green) is reading -0.03V (yes negative)
CO Trim (Red/Blue) is 11.9V
Supply (Orange/Brown) is 11.9V
I also have another modified AFM that I know had a fault. It was originally supplied by the Late Ian Whalley (Surname??) I repaired it as it had soldering issues and used it as a 3rd test.
Signal (Blue/Green) is reading 0V
CO Trim (Red/Blue) is 2.33V
Supply (Orange/Brown) is 12V
In all cases the car wont run. If I clean the plugs it starts, then misfires and coughs to a halt. Interestingly though, I don't have the strong over fueling smell now.
I'm at a complete loss now. I have booked the car to a mechanic who is relatively inexperienced with the 14CUX but is awesome otherwise and is picking up some of the local TVR work now that we have lost Jim.
Here are my notes from testing.
I'd be very grateful for any guidance.
Steve
I started going through everything again with fresh eyes about a week or so ago. Here are my findings.
The ECU Wiring has been checked. I had an old wiring loom (From a Griff) that I used to confirm some things that I couldn't physically check. These are shown here;
Of Note and compared to the wiring provided by Steve_D, I don't think the Black/Red wire that connects the AFM and other sensors is directly connected to earth. Instead they all connect at the loop back connector and I assume earth return is via the ECU. Also, the Orange/Brown wire that provides 12V to the AFM via the main power relay is linked in the relay, so removing the relay from the socket separates the two lines so that they can be tested independently.
The advice to remove each sensor, Injector etc. was fantastic. I have now tested every wire for continuity, shorts against the battery +Ve and -Ve and every other pin on the ECU. There are no issues and this also proved how the lop back connector has grouped the wires.
Unfortunately though, I have still not found the issue. In addition to the wiring checks, I have
Put the old ignition coil back in
Changed the plugs back to the original and installed the spark plug shrouds
Checked all tests listed in the 14CUX manual (actually I haven't checked everything - but have all the ones I think needed to be)
Checked voltage and resistance across everything I can check.
The results generally within spec except the AFM. I have two AFM's that were both okay before I did any work on the car. Both test exactly the same.
Signal (Blue/Green) is reading -0.03V (yes negative)
CO Trim (Red/Blue) is 11.9V
Supply (Orange/Brown) is 11.9V
I also have another modified AFM that I know had a fault. It was originally supplied by the Late Ian Whalley (Surname??) I repaired it as it had soldering issues and used it as a 3rd test.
Signal (Blue/Green) is reading 0V
CO Trim (Red/Blue) is 2.33V
Supply (Orange/Brown) is 12V
In all cases the car wont run. If I clean the plugs it starts, then misfires and coughs to a halt. Interestingly though, I don't have the strong over fueling smell now.
I'm at a complete loss now. I have booked the car to a mechanic who is relatively inexperienced with the 14CUX but is awesome otherwise and is picking up some of the local TVR work now that we have lost Jim.
Here are my notes from testing.
I'd be very grateful for any guidance.
Steve
I forgot to mention that I also got my Roverguage thing working. It showed up faults 12 and 18. I cleared the faults and they showed up again after a few minutes. Interesting the Ian Whalley AFM has not thrown up these faults but the car still doesn't run. This AFM is probably throwing me off rather than helping.
![](https://thumbsnap.com/sc/JSST2fYK.png[/img]</a> <a href="https://thumbsnap.com/eQudUcWQ" Target="_blank" rel="nofollow">[img]https://thumbsnap.com/sc/eQudUcWQ.png)
Ive not read the whole thread, but you should caption your rovergauge screenshots so we know what you're doing.
eg in the first ones the top row is being used in the map, in tne lower ones the bottom row is being used. the throttle position sensor records a change between them, were you blipping the throttle or out on the road or something, because neither situation should really occur unless you are on a trailing throttle downhill 9top row being used) or under full load up hill 9bottom row being used.)
If you were just in the garage with closed throttle, or lightly revving it, then youve found your visual symptom referenmce, if not the root cause ..
eg in the first ones the top row is being used in the map, in tne lower ones the bottom row is being used. the throttle position sensor records a change between them, were you blipping the throttle or out on the road or something, because neither situation should really occur unless you are on a trailing throttle downhill 9top row being used) or under full load up hill 9bottom row being used.)
If you were just in the garage with closed throttle, or lightly revving it, then youve found your visual symptom referenmce, if not the root cause ..
spitfire4v8 said:
I've not read the whole thread, but you should caption your rovergauge screenshots so we know what you're doing.
eg in the first ones the top row is being used in the map, in the lower ones the bottom row is being used. the throttle position sensor records a change between them, were you blipping the throttle or out on the road or something, because neither situation should really occur unless you are on a trailing throttle downhill 9top row being used) or under full load up hill 9bottom row being used.)
If you were just in the garage with closed throttle, or lightly revving it, then you've found your visual symptom reference, if not the root cause ..
Understood, all the screenshots were taken with the car parked and me attempting to run the engine by keeping the throttle open between just open and half. The engine ran for about 2 minutes then I stopped it as it was progressively getting rougher. So cold start, out of gear and parked, throttle blipping to keep the car running and trying to find a point that it "Might clear". eg in the first ones the top row is being used in the map, in the lower ones the bottom row is being used. the throttle position sensor records a change between them, were you blipping the throttle or out on the road or something, because neither situation should really occur unless you are on a trailing throttle downhill 9top row being used) or under full load up hill 9bottom row being used.)
If you were just in the garage with closed throttle, or lightly revving it, then you've found your visual symptom reference, if not the root cause ..
SteveSNZ said:
Understood, all the screenshots were taken with the car parked and me attempting to run the engine by keeping the throttle open between just open and half. The engine ran for about 2 minutes then I stopped it as it was progressively getting rougher. So cold start, out of gear and parked, throttle blipping to keep the car running and trying to find a point that it "Might clear".
In that case you have a problem .. the top row of the fuel map is for over-run conditions, the bottom row is for full throttle .. the reason for the issue however I don't know, but that's definitely an issue.Another update..
I had a spare AFM connector plug from another loom. I spliced it to the car loom, close to the ECU plug and now I get different readings but the same problem. Using the repaired AFM
AFM Signal 1.75V and AFM CO trim 3.24V.
On Roverguage, I noticed the MAF CO Trim reads as 2.5V which I believe is the outcome you get when the AFM is faulty.
I then plugged in my original AFM, the voltage readings are the same (1.75V and 3.24V), however in Roverguage the CO Trim is reading as 1.26V. The engine still struggles to start and when it does, it cuts out after a few seconds.
I videoed the attempts and have some screenshots. This is with my original AFM, plugs removed and cleaned, engine cranked to clear an residual gasses, plugs back in. In the garage, not moving, cold start.
Images: Before attempting Start
MAF reading = 0. CO Trim = 1.25V
Engine starts well + 1 second.
MAF reading = moves a bit then looks to stick for a moment at 50%. CO Trim = 1.25V
Half a second later - here the AFM reading moves to about 75%, everything is looking good with the engine been running for the 1st second or so. Then, MAF CO trim changes to 2.5V and the engine cuts out.
Engine now fails to start. The MAF reading is sitting at 40% with the engine stopped.
Now with the engine dead, the MAF reading is still 40% or so and the CO Trim is still 2.5V.
I messed around for a while longer. I did get a MIL light on but no fault codes. No fault codes came up again but the MIL light did flash on and off again, then a laptop restart sorted that.
I then checked I was getting a spark at each plug (timing light and turned the engine over), each one flashed.
Then I gave up and had a beer.
I had a spare AFM connector plug from another loom. I spliced it to the car loom, close to the ECU plug and now I get different readings but the same problem. Using the repaired AFM
AFM Signal 1.75V and AFM CO trim 3.24V.
On Roverguage, I noticed the MAF CO Trim reads as 2.5V which I believe is the outcome you get when the AFM is faulty.
I then plugged in my original AFM, the voltage readings are the same (1.75V and 3.24V), however in Roverguage the CO Trim is reading as 1.26V. The engine still struggles to start and when it does, it cuts out after a few seconds.
I videoed the attempts and have some screenshots. This is with my original AFM, plugs removed and cleaned, engine cranked to clear an residual gasses, plugs back in. In the garage, not moving, cold start.
Images: Before attempting Start
MAF reading = 0. CO Trim = 1.25V
Engine starts well + 1 second.
MAF reading = moves a bit then looks to stick for a moment at 50%. CO Trim = 1.25V
Half a second later - here the AFM reading moves to about 75%, everything is looking good with the engine been running for the 1st second or so. Then, MAF CO trim changes to 2.5V and the engine cuts out.
Engine now fails to start. The MAF reading is sitting at 40% with the engine stopped.
Now with the engine dead, the MAF reading is still 40% or so and the CO Trim is still 2.5V.
I messed around for a while longer. I did get a MIL light on but no fault codes. No fault codes came up again but the MIL light did flash on and off again, then a laptop restart sorted that.
I then checked I was getting a spark at each plug (timing light and turned the engine over), each one flashed.
Then I gave up and had a beer.
spitfire4v8 said:
What happens if you disconnect the afm, then start the car.
With the afm disconnected before turning ign on the ecu will run throttle angle v revs . is it better. worse. or the same?
The outcome is the same, but I haven't been able to grab logs until yesterday so I cant compare logs. But the voltage and behaviors is the same. With the afm disconnected before turning ign on the ecu will run throttle angle v revs . is it better. worse. or the same?
Steve_D said:
Rob is the name of my car. Those wiring diagrams are mine (and available to anyone who wants them).
Rovergauge is a must as it can answer many questions like, is the ECU seeing the correct temperatures for both fuel and coolant temperatures i.e. with the engine cold both readings should be about the same and read ambient temp. It will also show if the ECU is using the right fuel map. The map is set by a 'Tune Resistor' so any poor connection could cause the ECU to use the wrong map.
The blue 'Loopback Connector' or header is a way of joining together wires of a like function. There are 4 'functions' passing through this connector being...
Ignition switched 12 volt. mainly white/green wires with 1 black going to the coil.
+12V from the main ECU relay. 4 Brown/orange wires.
Earths. Possibly 6 wires black or Black/Slate.
Sensor earths. Possibly 6 wires all Black/Red. These are sensor earths connecting back to the ECU so should only be tested for resistance with all the sensors and the ECU disconnected otherwise false readings can occur such as Steve has already mentioned.
This connector lives in the footwell so (for a UK car) could be a rather damp environment and I have seen a number of cars with corrosion in this area (and in ECUs).
If corrosion is present then each group of wires should be cut from the connector, stripped back to clean copper and soldered together as a group and finally sealed.
Were all the plugs fouling or just one bank? Have seen a situation where the number 1 injector wire (that connects to the ECU) had chaffed through on the coil mounting bracket and earthed so all the injectors were wide open on that bank.
Steve
I commented above that my wiring is different from your diagrams, but its not. Sorry I misunderstood what one of the connections was smileRovergauge is a must as it can answer many questions like, is the ECU seeing the correct temperatures for both fuel and coolant temperatures i.e. with the engine cold both readings should be about the same and read ambient temp. It will also show if the ECU is using the right fuel map. The map is set by a 'Tune Resistor' so any poor connection could cause the ECU to use the wrong map.
The blue 'Loopback Connector' or header is a way of joining together wires of a like function. There are 4 'functions' passing through this connector being...
Ignition switched 12 volt. mainly white/green wires with 1 black going to the coil.
+12V from the main ECU relay. 4 Brown/orange wires.
Earths. Possibly 6 wires black or Black/Slate.
Sensor earths. Possibly 6 wires all Black/Red. These are sensor earths connecting back to the ECU so should only be tested for resistance with all the sensors and the ECU disconnected otherwise false readings can occur such as Steve has already mentioned.
This connector lives in the footwell so (for a UK car) could be a rather damp environment and I have seen a number of cars with corrosion in this area (and in ECUs).
If corrosion is present then each group of wires should be cut from the connector, stripped back to clean copper and soldered together as a group and finally sealed.
Were all the plugs fouling or just one bank? Have seen a situation where the number 1 injector wire (that connects to the ECU) had chaffed through on the coil mounting bracket and earthed so all the injectors were wide open on that bank.
Steve
blitzracing said:
Ive not read all the posts but here are the basics on a rich mixture.
Both banks over fuelling- AFM. - voltage output too high - check it with no airflow- should be around .3 to .34 volts . This is important if its higher all the AFM output will be wrong across the whole range. Another point is the CO trim voltage stuck high. Check the CO trim as per the G33 web page- it should be possible to change the engine note winding the voltage up and down as it goes rich or lean just like adjusting a carb idle mixture. Low voltage lean, high rich. The CO trim is a 5 k resistor to ground that pulls the ECU supplied 5v down to the trim voltage. If its open circuit you get 5v at the ECU and highly over fuelling. Trim voltage is normally between 1.4 and 1.8 volts. Also make sure the AFM plug / cable are not damaged.
Temp sensors- you have checked them but you can double check with a cold engine when both fuel rail and water temp should be near the same as the devices are electrically the same.
Fuel pressure too high. Lost vacuum to the regulator or blocked fuel return pipe
Stuck injectors- only happens on one bank at a time if the injector loom shorts to ground and opens the injectors constantly.
Just a note on "common" grounds. The AFM has a dedicated ground wire back to the ECU as does the TPS as small signals going back through the engine ground plane could be altered by stray ground voltages. Sensors must be measured on there own ground wires and not the engine block.
At this point I don't smell as much unburnt fuel in the garage when I'm testing. The plugs aren't as wet but now the car only runs for a couple of seconds then wont start without all the plugs being removed, cleaned and installed again. Its becoming very challenging to have any confidence in what's actually going on.Both banks over fuelling- AFM. - voltage output too high - check it with no airflow- should be around .3 to .34 volts . This is important if its higher all the AFM output will be wrong across the whole range. Another point is the CO trim voltage stuck high. Check the CO trim as per the G33 web page- it should be possible to change the engine note winding the voltage up and down as it goes rich or lean just like adjusting a carb idle mixture. Low voltage lean, high rich. The CO trim is a 5 k resistor to ground that pulls the ECU supplied 5v down to the trim voltage. If its open circuit you get 5v at the ECU and highly over fuelling. Trim voltage is normally between 1.4 and 1.8 volts. Also make sure the AFM plug / cable are not damaged.
Temp sensors- you have checked them but you can double check with a cold engine when both fuel rail and water temp should be near the same as the devices are electrically the same.
Fuel pressure too high. Lost vacuum to the regulator or blocked fuel return pipe
Stuck injectors- only happens on one bank at a time if the injector loom shorts to ground and opens the injectors constantly.
Just a note on "common" grounds. The AFM has a dedicated ground wire back to the ECU as does the TPS as small signals going back through the engine ground plane could be altered by stray ground voltages. Sensors must be measured on there own ground wires and not the engine block.
Edited by blitzracing on Tuesday 11th April 17:10
Edited by blitzracing on Tuesday 11th April 17:26
DVR V8 said:
The connector you mentioned with the melted wire is called a header , just a way of connecting multiple wires together. The blue header is a group of grounds. The 14 CUX ignition system does not have OBD. Regards. Edited by DVR V8 on Saturday 1st April 20:02
Not sure what you have bypassed but the blue loop back connector contains different circuits.
Info here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Info here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Belle427 said:
Not sure what you have bypassed but the blue loop back connector contains different circuits.
Info here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
What I've done is spliced in a 2nd plug that connects the wiring to the AFM. Effectively running 2 sets of wired to each source, connecting the 2nd plug in parallel to the original one. The reasoning is that if the original plug had an internal connection issue, the 2nd one would hopefully be okay. I have now cut the original plug from the loom, only leaving the 2nd one connected. No Change. Info here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
I have also tried moving the ignition leads around, just in case a basic error was made. I moved the leads to opposite side of the disty (just in case the rotor is 180Deg out) = Top image. Then I move the leads one step clockwise = bottom left image. Then one step anticlockwise (from the start position) = bottom right image. The red numbers represent the leads and the black represent the disty cap. The small squares are where my clips are in relation to the plugs. Yes I'm clutching at straws... no change.
Car still doesn't start now. Although I expect if I spent another hour removing the plugs between each change then it might.
Also, I connected a lead to a spare spark plug, the spark jumped to the engine over a distance of about 15mm. So I think the spark is good.
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