420s throttle hesitation/surge when car doing light throttle and car running 30+ mins

[Ant2]

On to the latest issue.

I have a 420s with jenvey throttle bodies, recently had issues with idling at 2.5k, hesitation pulling off etc.

Apparently it was the tps connector, this got chopped off and spade connections instead. This fixed the idle issues and hesistation when pulling off.

But it also had another issue, which I thought was related and resolved,  but isn't 

After 30 or so minutes (motorway seems to be the only way to reproduce this) when holding a speed i.e 70mph i het surges where the car loses power, very minor level though and then if i drop the throttle more it still jolts a bit but goes away, same on acceleration or just leaving it.. I find if i put harder throttle the issue doesn't happen, but the issue can sometimes continue as much as several times per minute, to only 3 times in the next 20 minutes. 

Feels like a misfire/fueling issue

 

The fact this was only noticeable around the time of the tps issue makes me a little suspicious.  Has any one had similar issues and found out what causes it?

It does seem related to the car running a long time with no breaks and little throttle and it's intermittenet..

I found some (similar) looking threads but nothing concrete.

[aerobod - near CYYC]

I had a similar issue due to a dodgy connection on #1 coil pack. There have also been others with fractured wires if you don’t have the upgraded silicone insulated coil pack loom. Vibration, heat and low or high load conditions seem to exacerbate the issue. I needed to run a recording USB oscilloscope to capture the problem. My issue was caused by vibration causing the connector to become a bit loose (could see slight arcing on the contacts with a magnifying glass), solved for the past couple of years by applying foam tape to the connector on the coil to apply slight pressure against the coil cover to eliminate vibration.

[Ant2]

2 minutes ago, aerobod - near CYYC said:

I had a similar issue due to a dodgy connection on #1 coil pack. There have also been others with fractured wires if you don’t have the upgraded silicone insulated coil pack loom. Vibration, heat and low or high load conditions seem to exacerbate the issue. I needed to run a recording USB oscilloscope to capture the problem. My issue was caused by vibration causing the connector to become a bit loose (could see slight arcing on the contacts with a magnifying glass), solved for the past couple of years by applying foam tape to the connector on the coil to apply slight pressure against the coil cover to eliminate vibration.

Thanks for the feedback. Could you send me a picture of how it looks as I wonder if it's worth taping all 4 just to see if it goes away!

Mine doesn't appear to be high load though,  only low and static. Which is strange as i would expect bumpy roads to cause this to happen more if it was a coil coming loose.

Will look at the wires on the loom too.

[Colin_T]

Would Dow Corning dc4 compound help on the coil connections ? 
 

[aerobod - near CYYC]

1 hour ago, Ant2 said:

Thanks for the feedback. Could you send me a picture of how it looks as I wonder if it's worth taping all 4 just to see if it goes away!

Mine doesn't appear to be high load though,  only low and static. Which is strange as i would expect bumpy roads to cause this to happen more if it was a coil coming loose.

Will look at the wires on the loom too.

I have a foam strip on the underside of the coil cover with 3mm thick foam tape (the same as used on the edge of the bonnet). You can see the indentations in the foam the correspond with the coil connectors:

I also have a few pieces of 6mm foam tape on the top of the coil cover to stop it scraping/vibrating against the underside of the bonnet:

[Ant2]

12 hours ago, aerobod - near CYYC said:

I have a foam strip on the underside of the coil cover with 3mm thick foam tape (the same as used on the edge of the bonnet). You can see the indentations in the foam the correspond with the coil connectors:

I also have a few pieces of 6mm foam tape on the top of the coil cover to stop it scraping/vibrating against the underside of the bonnet:

I've scanned the ecu and see a pending tps fault logged.

When i look at the throttle position it always starts above 35, even though its closed.

It goes to 61.57 when fully open.

The sensor must be working somewhat as it's reading something,  but i read it should start from 0, is this correct?

I wonder if one of the spade wires isn't quite crimped properly or would the high reading and engine fault just suggest the sensor as a whole is faulty?

[aerobod - near CYYC]

I don’t think the OBD scanner TPS reading is particularly useful, the car wouldn’t run at all if the values were out by such a large amount. It is likely that the CAN PID 71 that is showing Absolute Throttle Position B is not configured for the percentage to map to the raw TPS voltage correctly. The 9A4 ECU can have all sorts of CAN message configuration, but by default not much is used or calibrated appropriately. To check the CAN config you need Easimap and an MBE 985 cable.

The PID 71 has a single byte resolution so can report 255 values, you can see that in your graph showing a 0.4% resolution between the data point values, but the standard MBE CAN output is not throttle % but raw voltage over 2 bytes giving 65535 values, so this further confirms the OBD scanner is not really showing calibrated TPS values.

The variation in your graph of 3/255 (1.2%) of the TPS range at idle is not unexpected, there is engine vibration that can cause a bit of throttle body blade movement on the stop and some voltage variation that can also cause a bit of noise in the signal, 0.04V over the typical 4.2V range from idle to full throttle or about 1% of the throttle range is quite normal.

The TPS fault is also not unexpected, it depends on the TPS failure limits set in the ECU. If the minimum failure voltage has been set to the lowest idle voltage expected, then the slight variability of the TPS voltage can send it below this value generating a benign error, again, another setting that can only be seen in Easimap.

Overall I don’t think there is anything that points to a TPS issue at the moment, just the limitations of what can be seen on an OBD scanner vs what Easimap can show.