I'm stumped... EFI/ITBs have no throttle response. Help!?

[Gabe.]

Morning everyone!

I posted up some issues I was having with my engine in my build thread over the last week and haven't been getting much traction. Felt like opening it up to more people may bring some more knowledge.

It's an 86 911 with 10.5:1 JE Pistons, Twin Coil on Plug, DC 44 cams, Triumph ITBs, running an MS3 Pro on Alpha N. It has had 800 miles of trouble-free enjoyment *except for sucking debris into cylinder #2 and me having to take it apart and fix some things about 75 miles ago*.

It drove well on Saturday and then when out driving on Sunday it started misfiring and now has absolutely no throttle response off idle. If I build the revs slowly past 2500 rpms it will then have more normal throttle response. The idle is really low ~450-500rpms when it was stable at about 750-800 rpms before. The way it sits now it's pretty undrivable.

This is what it was doing when I got it home on Sunday:



Here's what I've done since Sunday:

• Compression Test. All came back the same as they were before. Cylinder #2 hasn't had the rings seat yet, it's only been driven 75 miles.
• Leakdown test, all the same as before. Results are positive and there are no issues here other than cylinder #2 that needs the rings to be broken in.
• Checked ignition timing, my Tooth #1 Angle was off 10 degrees. When I first got the car done it wasn't a reliable trigger, this time I'm confident with it. It's set at 60 degrees and with the timing fixed to zero it's firing at the TDC mark. I've also adjusted most of the ignition map to compensate for the change, it was really conservative before (2/5 degrees timing advance at idle). This could definitely be an area of concern but with the car having been driving fine before, I'm not sure how important this is.
• Double checked mechanical timing. Yes, I took the back of the engine apart and spilled oil all over my garage floor again. DRC specs at 3.0-3.2mm for my cams with .004" valve clearance at TDC. It's at 0.120" which is about 3.05mm. It's the same for both left and right side cams.
• Checked valve springs, retainers, rocker arms, and while I was in there I adjusted all the valve clearances and double-checked head stud torque.
• New spark plugs (NGK BCPR7es gapped to .035") and I also tested out another set of OEM Audi R8 ignition coils I had lying around.
• Confirmed fuel pressure is steady. You can see the gauge in the videos and it's stable.
• ITBs are synced and pulling ~6-7 on my synchrometer.
• Hooked up my mity vac (it's the only vacuum gauge I have) and it was ~5 in hg at idle, which seems low but I have no idea what it should be or was before on a car with ITBs.

Here is a vid of how it's running now:



Electrically there are seven sensors that contribute to how the ecu makes the car run

• Crank Sensor
• Cam Sensor (which is hooked up but not yet being used for full sequential)
• Intake Air Temp sensor
• Throttle Position sensor
• Cylinder Head Temp sensor
• Wideband O2 sensor. AEM sensor running CAN so it's getting a direct signal into the ECU.
• Manifold Absolute Pressure sensor. I'm running the MAP sensor that's internal to my MS3 Pro. I'm running an Alpha N tune which uses throttle position to work it's way through the VE table and the MAP sensor is a secondary sensor.

All the sensors seem to be operating as they should according to the readouts I see in Tunerstudio. The map sensor seems to be slow to respond but since it's Alpha N it should only be using that secondarily and I didn't pay enough attention to it earlier to know if it actually is being slow.

After doing a full health check, I'm pretty stumped and would love any ideas of what to check next from the Pelican brain trust. My thought is to see if there are any intake leaks anywhere. Either take the ITBs off the heads and check the intake manifold spacers and gaskets or build something to pressure/vapor test each throttle body. After having sprayed starting fluid around each vac line with no change in idle I'm not sure I'll find anything. I'm grasping at straws at this point.

I don't understand how it can run perfectly on Saturday and then not on Sunday. The only difference between the two driving sessions was being in traffic for a bit before getting up in the canyons on Sunday.

This is a bit longer vid with some readouts from Tunerstudio.



Let me know if any of you have any thoughts. I'm eager to learn new problem solving techniques or hear theories about what's happening.

Thank you for all your help!

[anthony 911]

Start the car up and spray water on each cylinders exhaust you will find your problem

[Gabe.]

Originally Posted by anthony 911

Start the car up and spray water on each cylinders exhaust you will find your problem

I thought you were a little crazy... Turns out the entire passenger side bank isn't firing despite injectors and ignition working in test mode.

I've checked and we're getting fuel but the spark isn't as strong on the passenger as it is on the driver side.

I'm going to go through all the ignition wiring again.

[Gabe.]

Well, it pays to be thorough.

I cleaned all the grounds again and still wasn't having much luck...

These ignition coils have four pins
A - 12v power
B - ground
C - signal from ecu
D - another ground

I was getting full battery voltage between pins A and D but not A and B. After some more poking and proding, I found that I had a grounding issue with all the B grounds which are terminated at the cylinder head.

I cleaned the bolt, bolt threads, washer, and the terminal and still wasn't getting a good ground.

Blasted the bolt hole out with brake clean and compressed air, put everything back together and... WE HAVE 12 VOLTS! Yay. I suspect that there was some oil in that hole from taking the engine apart.

Now to put it back together, test the spark, and then see if it fires.

With all 12 ignition coils tested and operable, I put the fuel pump relay fuse back in, turned the key, and it fired right up!

Just goes to show, don't overlook the simple stuff... Glad I relearned that today. Thanks for all your help!

[Mixed76]

Well done!

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[kjellr]

I have same setup only dc43-108 cams JE11.5 pistons, check with the syncronometer under different rpm`s if the values stays the same.

Adjust accel enrichment

Are you using itb fuel load?

How is your ing timing table?




I use full squense and here is my injector timing

[Gabe.]

Originally Posted by Mixed76

Well done!

Thank you!

Originally Posted by kjellr

I have same setup only dc43-108 cams JE11.5 pistons, check with the syncronometer under different rpm`s if the values stays the same.

Adjust accel enrichment

Are you using itb fuel load?

How is your ing timing table?

I use full squense and here is my injector timing

Figuring out a new ignition map is one of my next priorities.

Here's what it looked like prior to me finding the tooth #1 angle being off by ten degrees:



Pretty conservative for a twin plug, but if it was off by ten degrees that meant that it became quite a bit more aggressive.

It didn't really like the conservative map once I got the car running again so I went back to the forums to cobble something new together. It's not easy to find ignition maps for a twin plug engine so I used a 95 993 timing table as a starting point. It seems to be aggressive/conservative in odd places though. With some changes, this is where I'm at:



I'm going to need to figure out a hybrid between my old map and this one, there are clearly some weird things going on in that map, still a work in progress. Right now it's not loving cold starts or RPM between 1000 - 2000 RPM while cold. Once it's warm, it's fine.

I'd like to get it dyno tuned professionally so I know it's both right and what sort of power it's making. Once Cylinder #2 is broken in and has good compression, I'll find somewhere to get that organized.