Problems since fitting ACT twin plenum
Discussion
I’ve recently fitted an ACT twin carbon plenum, but still having issues getting the car running.
The car idles perfectly, but as soon as i increase the revs, the engine stutters and runs really lean (off the scale on my AFR gauge). The symptoms would indicate a vacuum leak, but I have refitted the plenum a couple of times now and was pretty confident after testing that it was sealing this time.
Before I take it off and refit again, I just wanted to check if there are any other obvious faults I’m missing. The car hasn’t been run on the road since December so it’s possible there is another issue.
The car idles perfectly, but as soon as i increase the revs, the engine stutters and runs really lean (off the scale on my AFR gauge). The symptoms would indicate a vacuum leak, but I have refitted the plenum a couple of times now and was pretty confident after testing that it was sealing this time.
Before I take it off and refit again, I just wanted to check if there are any other obvious faults I’m missing. The car hasn’t been run on the road since December so it’s possible there is another issue.
I took a few logs from the ECU (megasquirt) which didn’t identify any problems, other than the high AFRs. Also added some fuel to the map in the low load areas just above the idle. This did reduce the AFRs a bit, but didn’t make it run any better. I wouldn’t really expect the map to be far out at low loads anyway. Also the TPS was reclibrated and tested so i dont think its the cyurrent map thats the problem.
During the installation I did have to replace the plug for the TPS sensor, the wiring for this runs through the same loom as the injectors, so it possible that I could have disturbed the wiring to one of the injectors, or even just dislodged one of the injector plugs. If fuel is only getting to 7 cylinders then this could explain the symptoms and why the engine still runs when the AFR is so lean. Ill have abnother look tonight and check the injectors etc.
During the installation I did have to replace the plug for the TPS sensor, the wiring for this runs through the same loom as the injectors, so it possible that I could have disturbed the wiring to one of the injectors, or even just dislodged one of the injector plugs. If fuel is only getting to 7 cylinders then this could explain the symptoms and why the engine still runs when the AFR is so lean. Ill have abnother look tonight and check the injectors etc.
Low revs / light throttle is exactly where you'd expect to have the problem if you're using tps v revs for your mapping. The rate of change of airflow from the act twin with be far greater than from your old single butterfly.
Log the afrs and update your fuel map accordingly, but you'll not be able to do much with the ignition which will now have too much advance per throttle degree assuming this was correct beforehand.
Log the afrs and update your fuel map accordingly, but you'll not be able to do much with the ignition which will now have too much advance per throttle degree assuming this was correct beforehand.
angus337 said:
I took a few logs from the ECU (megasquirt) which didn’t identify any problems, other than the high AFRs. Also added some fuel to the map in the low load areas just above the idle. This did reduce the AFRs a bit, but didn’t make it run any better. I wouldn’t really expect the map to be far out at low loads anyway. Also the TPS was reclibrated and tested so i dont think its the cyurrent map thats the problem.
During the installation I did have to replace the plug for the TPS sensor, the wiring for this runs through the same loom as the injectors, so it possible that I could have disturbed the wiring to one of the injectors, or even just dislodged one of the injector plugs. If fuel is only getting to 7 cylinders then this could explain the symptoms and why the engine still runs when the AFR is so lean. Ill have abnother look tonight and check the injectors etc.
But was the TPS re-calibrated in the software ? During the installation I did have to replace the plug for the TPS sensor, the wiring for this runs through the same loom as the injectors, so it possible that I could have disturbed the wiring to one of the injectors, or even just dislodged one of the injector plugs. If fuel is only getting to 7 cylinders then this could explain the symptoms and why the engine still runs when the AFR is so lean. Ill have abnother look tonight and check the injectors etc.
spitfire4v8 said:
Low revs / light throttle is exactly where you'd expect to have the problem if you're using tps v revs for your mapping. The rate of change of airflow from the act twin with be far greater than from your old single butterfly.
Log the afrs and update your fuel map accordingly, but you'll not be able to do much with the ignition which will now have too much advance per throttle degree assuming this was correct beforehand.
I did try and calculate the difference in air flow for the twin 52mm vs single 71mm intakes. the difference in overall crosssectional area is only about 7.5%, so In terms of the flow vs percentage open I didn't expect there to be alot of difference at low loads. Log the afrs and update your fuel map accordingly, but you'll not be able to do much with the ignition which will now have too much advance per throttle degree assuming this was correct beforehand.
A comparison of valve flow coeffecient vs % open for a single 71mm vs 2x52mm valves would look something like this, based on a typical butterfly valve characteristic
Well In theory, assuming the TPS sensor is reading the actual valve position then there the shouldn’t be much difference at low loads, however I have had another look at my fuel map, and it does seem to be very flat at low TPS, compared to other examples and the base map I started with. So I’m thinking that the old TPS sensor may have been offset vs the trottle position.
Anyway Just put some fresh fuel in and tried adjusting with tuner studio and I’m now getting some noticeable improvements. So looks like a mapping issue after all. Only downside is I think I’m going to have to redo the whole map.
Couldn’t really do much more in the garage and and keep on good terms with the neighbours, so taken a few logs and settled down with a gin (or 5) to try and tidy up the map.
Anyway Just put some fresh fuel in and tried adjusting with tuner studio and I’m now getting some noticeable improvements. So looks like a mapping issue after all. Only downside is I think I’m going to have to redo the whole map.
Couldn’t really do much more in the garage and and keep on good terms with the neighbours, so taken a few logs and settled down with a gin (or 5) to try and tidy up the map.
How has this ended up for you Nick, has some work on your fuel table helped solved the lean condition or do you still suspect an underlying vacuum leak?
Is it really the case just switching to the ACT twin arrangement demands such fueling changes? I certainly know of others who've faced sealing issues with this setup, if a vacuum leak remains the true source of the problem you'd certainly not be alone in meeting this challenge with the ACT twin.
Clearly the only way to fix a vacuum leak is to track it down and eliminate it in the first place, mapping it out is not the solution so do keep in mind masking a vacuum leak by throwing fuel at it may well solve the issue in one area but will also likely still leave you with drivability and idle stability issues, so I'd be interested to know how the setup is performing for you in these respects.
I'm tempted by the ACT twin throttle plenum myself so am very keen to hear your feedback, reports of the significantly enhanced throttle response it delivers make the setup very tempting to me, but not if it comes with frustrating sealing issues, negative impacts on drivability and idle quality.
Thanks in advance for your candid feedback and review of the ACT twin
Is it really the case just switching to the ACT twin arrangement demands such fueling changes? I certainly know of others who've faced sealing issues with this setup, if a vacuum leak remains the true source of the problem you'd certainly not be alone in meeting this challenge with the ACT twin.
Clearly the only way to fix a vacuum leak is to track it down and eliminate it in the first place, mapping it out is not the solution so do keep in mind masking a vacuum leak by throwing fuel at it may well solve the issue in one area but will also likely still leave you with drivability and idle stability issues, so I'd be interested to know how the setup is performing for you in these respects.
I'm tempted by the ACT twin throttle plenum myself so am very keen to hear your feedback, reports of the significantly enhanced throttle response it delivers make the setup very tempting to me, but not if it comes with frustrating sealing issues, negative impacts on drivability and idle quality.
Thanks in advance for your candid feedback and review of the ACT twin
Only managed a short drive round the block so far, due to a minor problem with the throttle return spring. The plenum was bought second hand and it looks like the spring on the throttle pot isn’t installed correctly. Ordered new springs from ACT and in the meantime got on with suspension and brake upgrades.
From the short drive I managed, it seems that the fuel adjustments have solved the problem, although there’s quite a bit of tweaking left to do on the fuel table and also the AE. I did speak with ACT before installation and they didn’t expect major changes to the fuel map at low load. So I was only expecting to have to increase the fuelling by a few percent to get it running smoothly. In reality I’ve had to almost double some of the areas on the table just above idle.
For info here’s my original fuel map compared to a base map I received from Phil when upgrading the ECU to wasted spark (looks very similar to Daz’s old Map?). I’ve re-ranged my table to match the RPM / TPS range from the base map, which shows more detail at low TPS. Whilst I wouldn’t expect the fuel values to match, the obvious difference is the shape of the curve. Mine is very flat low TPS and then very steep in the mid range (ignore the left hand side at Mid to High TPS and low revs as the car was never mapped in that area with the old set up)
The red circle indicates the area I’ve had to make major changes, but I haven’t adjusted the rest of the table yet..
Hopefully get everything running by the weekend and can report back.
From the short drive I managed, it seems that the fuel adjustments have solved the problem, although there’s quite a bit of tweaking left to do on the fuel table and also the AE. I did speak with ACT before installation and they didn’t expect major changes to the fuel map at low load. So I was only expecting to have to increase the fuelling by a few percent to get it running smoothly. In reality I’ve had to almost double some of the areas on the table just above idle.
For info here’s my original fuel map compared to a base map I received from Phil when upgrading the ECU to wasted spark (looks very similar to Daz’s old Map?). I’ve re-ranged my table to match the RPM / TPS range from the base map, which shows more detail at low TPS. Whilst I wouldn’t expect the fuel values to match, the obvious difference is the shape of the curve. Mine is very flat low TPS and then very steep in the mid range (ignore the left hand side at Mid to High TPS and low revs as the car was never mapped in that area with the old set up)
The red circle indicates the area I’ve had to make major changes, but I haven’t adjusted the rest of the table yet..
Hopefully get everything running by the weekend and can report back.
ChimpOnGas said:
I'm tempted by the ACT twin throttle plenum myself so am very keen to hear your feedback, reports of the significantly enhanced throttle response it delivers make the setup very tempting to me, but not if it comes with frustrating sealing issues, negative impacts on drivability and idle quality.
It should be fairly straightforward. However...I had my share of problems doing the install in the underground parking for the first time, all of them traceable to stupid 'beginner' faults and their knock-on effects.
The main culprit in my case was the stainless steel adapter plate not laying flat on the trumpet base. If the hex head fitting for the big vacuum line to/from the charcoal cansister is pointing upwards instead of having a flat side up top, you'll tighten the adapter plate and have an air leak. Then you tighten it some more and bend the adapter plate... The point here is that in confined areas (cars parked on either side of yours) and/or low light conditions, it's damn near impossible to see whether the plate seals properly to the trumpet base.
Another schoolboy error is to tighten the flange bolts holding the plenum to the trumpet base (with a cork gasket inbetween) rather too much, usually after you suspected an air leak and run out of ideas where it might come from (see above).
There's also been a small batch (two or three kits having been affected) where the plenums were incorrectly drilled after Jenvey changed the flanges of their DCOE throttle bodies, resulting in a customer of mine perfoming massive modifications to make it fit before any of us found out what the culprit was...
Now I can install, unbolt and put back twin and triple plenums in my sleep, first time right every time. It's really straightforward as long as you are methodical (I'm not, I had to learn the hard way
). 900T-R said:
The main culprit in my case was the stainless steel adapter plate not laying flat on the trumpet base. If the hex head fitting for the big vacuum line to/from the charcoal cansister is pointing upwards instead of having a flat side up top, you'll tighten the adapter plate and have an air leak. Then you tighten it some more and bend the adapter plate... The point here is that in confined areas (cars parked on either side of yours) and/or low light conditions, it's damn near impossible to see whether the plate seals properly to the trumpet base.
I had the same issue on my first attempt. took me ages to realise why i could get a seal at the trumpet base. Message Board | Chimaera | Top of Page | What's New | My Stuff