MFI Tuning help

[orange911]

OK,

I am in the final stages of CMA after doing the whole vacuum tester correlation and all:

MFI Correlation Questions

So after I got all parts re-installed, it runs like crap. What I have done since the throttle bodies were installed to try and make it better:

installed new Bosch 5DC plugs gapped at 0.028"

attempted to adjust part load mixture, but I could not tell if the screwdriver was egaged or not - really don't know what is in that hole and what resistance I am suppose to feel when turning. This may just need to be done in a shop

I have not touched the idle mixture

The synchrometer has been a great tool to verify the balancing of the TBs. When at idle, I used the by-pass screws to ensure balance all around. I ended up with 4 kg/hr. After that I ran the motor to 2000 and checked again. Left bank (1-3) is all equal at 18, and right bank is all equal at 16 kg/hr.

So, with this information, do I:
1) Adjust the throttle rod on the right bank so that it matches left bank
2) Adjust the throttle rod on the left bank so that it matches right bank
3) Adjust both to bring it to meet in the middle

After this adjustment, do I then readjust the air bypass at idle to sync with each bank?

[FenderBender]

Olin

To adjust the part load you need a very small slotted screw driver, you will feel it lock into the slot. When adjusting you should feel it click, make sure you count them so you can return it back if need be. Mine does not click so I marked a spot on my screw driver handle so I know how far I move it. Make small adjustments do not over do it.

I am not sure about the other adjustments but here is some good reading. Ultimate MFI resources thread

Good luck, Mike

[304065]

Olin,

Any competent porsche driver tracks faster if brakes come smoothly.

Air filter compression loss plugs dwell timing fuel pressure injectiors belt correlation smog.

I assume you have done all these items but didn't see a step-by-step rundown. You might post what you found.

OK, I am unclear as to whether you did get all the throttle plates set with the "vacuum flow bench" method, it looks like you got 5 at 3 Kg/hr and 1 at 3.5?

You use the side rods to set side-to-side correlation, subject to a max difference of 5mm in rod length. That isn't very much, but Porsche doesn't want you using the side rods to compensate for one throttle body that is worn more than the other. You should be able to balance them so you get the same reading at 3000 rpm. Watch yourself in the fan and belt while doing the checks.

Unless you have an LM-1 or other exhaust gas analyzer like a Gunson Gas Tester, it is very, very hard to get the mixture right. Do not monkey with the part load adjustment until you buy or borrow an LM-1 with an exhaust clamp- this will really allow you to see the part-load throttle (car in gear and brakes on, engine under load) at 3000 RPM. Measuring with no-load doesn't give you the right readings. LM-1s can be had cheaply these days.

What ignition system? That gap is a little narrow, I use 1mm but have MSD.

[orange911]

Mike,

Did you ever notice that the screwdriver can reach 2 depths? I noticed that it would seem to stop an inch or so in, then it would go even deeper? This really had me stumped.

[orange911]

Originally Posted by john_cramer

Olin,

Any competent porsche driver tracks faster if brakes come smoothly.

Air filter compression loss plugs dwell timing fuel pressure injectiors belt correlation smog.

I assume you have done all these items but didn't see a step-by-step rundown. You might post what you found.

OK, I am unclear as to whether you did get all the throttle plates set with the "vacuum flow bench" method, it looks like you got 5 at 3 Kg/hr and 1 at 3.5?

You use the side rods to set side-to-side correlation, subject to a max difference of 5mm in rod length. That isn't very much, but Porsche doesn't want you using the side rods to compensate for one throttle body that is worn more than the other. You should be able to balance them so you get the same reading at 3000 rpm. Watch yourself in the fan and belt while doing the checks.

Unless you have an LM-1 or other exhaust gas analyzer like a Gunson Gas Tester, it is very, very hard to get the mixture right. Do not monkey with the part load adjustment until you buy or borrow an LM-1 with an exhaust clamp- this will really allow you to see the part-load throttle (car in gear and brakes on, engine under load) at 3000 RPM. Measuring with no-load doesn't give you the right readings. LM-1s can be had cheaply these days.

What ignition system? That gap is a little narrow, I use 1mm but have MSD.

OK, air filter is new, compression is even, points replaced with pertronix, injectors cleaned, but pattern is not perfect, belt timing right on.

Timing is set with vacuum off at 5 degrees advance. Advance mechanism is getting above 30 degrees at high rpm, but did not test it at 6000 rpm. I assume it still has room to advance if I took it there.

Vacuum flow bench as you stated - 5 @ 3.0 kg/hr and 1 @ 3.5 kg/hr. After install and running, I set all to 4 kg/hr with all linkages off, rechecked after connecting linkages and made sure it was still 4 kg/hr. Difference was when I reached 2000 rpm, one bank different than the other.

I am using the Bosch CDI and it is humming and sparks are strong at the individual wires on the cap.

I think I read somewhere that the people were using 0.035 - 0.040, but the manual spec'd 0.025, which was how they were delivered, even though the box said 0.032". So I only opened them a bit to 0.028.

[orange911]

Originally Posted by john_cramer

You use the side rods to set side-to-side correlation, subject to a max difference of 5mm in rod length. That isn't very much, but Porsche doesn't want you using the side rods to compensate for one throttle body that is worn more than the other. You should be able to balance them so you get the same reading at 3000 rpm.

So if I understand this statement correctly, I should only open the one linkage from the control rod to the throttle body on the one that is low and leave the other side alone. This will take the throttles off the stops, right? Then I assume that I should close in the bypass screws to get idle flow balanced, correct?

[Grady Clay]

Olin,

Thanks for the ‘heads up’ PM. Sometime when not 10/10 I need a KITA.

… it runs like crap.

Can you be more specific? How well does it run full throttle above 4000 rpm? Will it idle at all? What are the idle symptoms? Are you absolutely sure of all the CMA details.

Are you sure of no vacuum leaks?
Are all the ball sockets clean and lightweight lube?
Are all the ball sockets, lock-nuts and rods free to turn?
Are all the lock-nuts finger tight?
When disconnected from any linkage, is the pump lever on the stop?
When you move the main rack (from the access above the drive tooth pulley), is it free to return to the closed stop?


You should be able to get all six flowing the same at idle first leaving the plates equal and on the stops and only using the bypass adjustments to equalize flow. Is this the case?

Now you need to adjust the throttle body rods so all the plates come off the stops at exactly the same time. This should not change the idle air flow when on the butterfly stops.

Next, connect and adjust the side rods (cross shaft-to-throttle body) so the butterfly plates come off the stops exactly the same time the pump lever comes off its stop. (This is one of the critical items.) Be sure to use the rod to the pedal to move the linkage. Any side movement of the cross shaft will fool you. So will pushing on a side rod or the pump rod.

When you first open the throttle (all seven come off stops), what happens? Does it ‘pop’ in the intake? Both sides, one side or one cylinder? Does the rpm increase? Does the rpm decrease? Don’t adjust anything yet. Re-check air flow for equal.

Using the hand throttle, idle up to, say, 1500 rpm. Measure the air flow. Are all six still equal? Is there an average difference left-to-right? How is the running? Smooth? Popping the intakes? Popping (rumble) in the muffler?


Now life will be much easier with an exhaust gas analyzer.



You need to adjust the main mixture with the screwdriver straight in the access hole. The ‘target’ is a screw slot about 3 mm long. It is surrounded by a circular metal piece about 5 mm diameter. The screw slot is below the edge of the circular piece. Any angle of the screwdriver, you can go past the side of the circular piece and not adjust anything. The circular piece tends to keep the screwdriver in the slot.

In the 2.2, 2.4, 2.7 & 3.0 there are twelve ‘clicks’ per 360° rotation of the screw. Keep track of every movement.

One of the most important admonitions in CMA it to go back and repeat. “…ask yourself whether all the points mentioned up to now have been conscientiously carried out Recheck any points of which you are not sure.” (Bold is from CMA.)

In many cases this means repeating CMA from scratch.
With our geriatric MFI, there is more than originally in CMA. Search Pelican on CMA2.

Best,
Grady

[orange911]

Originally Posted by Grady Clay

Olin,

Thanks for the ‘heads up’ PM. Sometime when not 10/10 I need a KITA.



Can you be more specific? How well does it run full throttle above 4000 rpm? Will it idle at all? What are the idle symptoms? Are you absolutely sure of all the CMA details.

It idles, but it sounds as if it could be missing and I can feel the engine shake from the seat more. I am going to revert back to the points tonight and see if that changes things. When running at 4000 and up, it pulls, but with random backfire. Since I do not have all the equipment a shop does, I will never be absolutely sure of CMA

Originally Posted by Grady Clay

Are you sure of no vacuum leaks?
Are all the ball sockets clean and lightweight lube?
Are all the ball sockets, lock-nuts and rods free to turn?
Are all the lock-nuts finger tight?
When disconnected from any linkage, is the pump lever on the stop?
When you move the main rack (from the access above the drive tooth pulley), is it free to return to the closed stop?

I put fresh gaskets on top of the heads and on top of the TB. Are there any other leak points outside of the vacuum port for distributor? All the ball sockets were cleaned, lubed with lightweight lube, balanced, and then lubed with grease and checked balance again. They are all free to turn by hand when the locknut is loose since I cleaned them all and ran the ball sockets all the way in and out with light oil (ATF).
I did not check the pump lever returns to its stop, and will do that this evening.

Tell me more about the main rack access, I am not familiar with what lurks from the rear of the pump.

[orange911]

Originally Posted by Grady Clay

You should be able to get all six flowing the same at idle first leaving the plates equal and on the stops and only using the bypass adjustments to equalize flow. Is this the case?

I used air flow from a vacuum to test when they begin to open (based on change of air flow rate) and locked each one. I can not say that they all are at the same degree, nor can I confirm that all air flow was equal with the by-pass screws closed. I will say that they were balanced first with the vacuum method with the by-pass screws and again while idling.

Originally Posted by Grady Clay

Now you need to adjust the throttle body rods so all the plates come off the stops at exactly the same time. This should not change the idle air flow when on the butterfly stops.

This is done and checked to be balanced at 4kg/hr with an idle around 1000

Originally Posted by Grady Clay

Next, connect and adjust the side rods (cross shaft-to-throttle body) so the butterfly plates come off the stops exactly the same time the pump lever comes off its stop. (This is one of the critical items.) Be sure to use the rod to the pedal to move the linkage. Any side movement of the cross shaft will fool you. So will pushing on a side rod or the pump rod..

I need to check this tonight. I had only inspected each side rod so that they open throttles on each side at the same time. Did not confirm pump lever off stop.

[orange911]

Originally Posted by Grady Clay

When you first open the throttle (all seven come off stops), what happens? Does it ‘pop’ in the intake? Both sides, one side or one cylinder? Does the rpm increase? Does the rpm decrease? Don’t adjust anything yet. Re-check air flow for equal.

There is popping and backfiring (fire) in the intake when activating the throttle. Several stacks are 'popping', but not much noise at idle. I really see the difference with the synchrometer in place. It fluctuates every time it 'spfs' or 'pops'. maybe two cylinders are dead on 4 kg/hr with no fluctuation. One of those without fluctuation is the number 3 cylinder that indicated more wear by not being able to get to 3 kg/hr on the vacuum bench. This cylinder also has the air bypass screw all the way closed.

I assume you are asking about the rpm increase/decrease with the pump rod disconnected? I tried this for experimenting and did notice the speed increase, but it still did not sound any better. How much should I open it to see an increase/decrease in rpm?

Originally Posted by Grady Clay

Using the hand throttle, idle up to, say, 1500 rpm. Measure the air flow. Are all six still equal? Is there an average difference left-to-right? How is the running? Smooth? Popping the intakes? Popping (rumble) in the muffler?

I used the hand throttle to measure at 2000 rpm and one bank (1-3) was at 18 kg/hr and the right (4-6) was at 16 kg/hr. Yet all were balanced at ~4 kg/hr on idle.

[cmcfaul]

Might be as simple as your timing. With the vacume hose on it should be 5 degrees ATDC. Thats after top dead center not before. 5 degrees advanced (btdc) at idle, even with the retard hose off, sounds too advanced.

Chris

73 911 E

[RSTarga]

If you are running original CDI I think your plugs need to be gapped much wider, check the factory specs .55 I believe but my memory fades. Until you get all the electrics in order do not adjust anything on MFI.
I think the stacks (screws) need to be synced at 3000 rpm. Which from my experience should be done with the factory tool, I think Stoddard sells them for 180dls. I was never successful with a unisyn but our host sells a newer too for much less that is supposed to work.
Do you have a copy of check measure adjust for MFI? It is available as a PDF, in the MFI section of this board. Last be carefull moving the adjustment mixture screw it has a spring that needs to be pressed in before it engages, I wouldn't move it more than 5 or 6 clicks. Don't do it while engine is running or you will damage the rack.

[orange911]

Originally Posted by Grady Clay

You need to adjust the main mixture with the screwdriver straight in the access hole. The ‘target’ is a screw slot about 3 mm long. It is surrounded by a circular metal piece about 5 mm diameter. The screw slot is below the edge of the circular piece. Any angle of the screwdriver, you can go past the side of the circular piece and not adjust anything. The circular piece tends to keep the screwdriver in the slot.

Did I get it right in the image below? I assume that the second bump is me going off the 5 mm disk and hitting the back. I was careful not to put too much pressure here from earlier reading. That was why I really did not feel comfortable in moving forward any more.

Will the screwdriver work if it is slightly wider than 3 mm; ie the screw protrudes out from the disk and has no boundries on the sides?. Does the disk turn with the screw or is it fixed?

[orange911]

Originally Posted by cmcfaul

Might be as simple as your timing. With the vacume hose on it should be 5 degrees ATDC. Thats after top dead center not before. 5 degrees advanced (btdc) at idle, even with the retard hose off, sounds too advanced.

Chris

73 911 E

I have it set at 5 degrees advanced with vacuum hose off and plugged

[orange911]

Originally Posted by RSTarga

If you are running original CDI I think your plugs need to be gapped much wider, check the factory specs .55 I believe but my memory fades. Until you get all the electrics in order do not adjust anything on MFI.
I think the stacks (screws) need to be synced at 3000 rpm. Which from my experience should be done with the factory tool, I think Stoddard sells them for 180dls. I was never successful with a unisyn but our host sells a newer too for much less that is supposed to work.
Do you have a copy of check measure adjust for MFI? It is available as a PDF, in the MFI section of this board. Last be carefull moving the adjustment mixture screw it has a spring that needs to be pressed in before it engages, I wouldn't move it more than 5 or 6 clicks. Don't do it while engine is running or you will damage the rack.

Yes, I am running the original Bosch CDI and you are correct that the factory specs are 0.55 mm, which equals 0.024". Since so many suggested wider gaps I only went to 0.028". My old plugs were gapped at 0.027" and that was ok.

If you are referring to the STH Synchrometer, that is what I have. I realize the CMA suggests 3000, but I only could hold 2000 with the throttle handle.

Thanks for the warning on the idle mixture screw, but I am still working on the feel of the part load screw. idle is the last one to adjust.

[cmcfaul]

I think your timing is way too advanced. Plug the hose back into the distributer and time it properly. I think you are off 5 -10 degrees too advanced (closer to 10). You set the timing using the left most line on the flywheel (5 degrees ATDC). The next line is TDC. The third line is 5 degrees BFTD (5 degrees advanced). Should be set at the first line at idle (5 degrees ATDC).

Your symptoms are exactly in line with f-ed up timing

Chris

73 911 E

[orange911]

Originally Posted by cmcfaul

I think your timing is way too advanced. Plug the hose back into the distributer and time it properly. I think you are off 5 -10 degrees too advanced (closer to 10). You set the timing using the left most line on the flywheel (5 degrees ATDC). The next line is TDC. The third line is 5 degrees BFTD (5 degrees advanced). Should be set at the first line at idle (5 degrees ATDC).

Your symptoms are exactly in line with f-ed up timing

Chris

73 911 E

Chris, thanks for following up. I am not sure if your 73 advances with vacuum or not, but my distributor retards on vacuum. This may be what is confusing. It is supposed to retard about 10 degrees, but it ain't getting all 10. That is why I plugged the port to set timing without vacuum to be advanced 5. That way timing may be slightly off at idle, but will be correct off idle. I was using the following from the CMA as a guide for this info.

[orange911]

Originally Posted by Grady Clay

Now you need to adjust the throttle body rods so all the plates come off the stops at exactly the same time. This should not change the idle air flow when on the butterfly stops.

Next, connect and adjust the side rods (cross shaft-to-throttle body) so the butterfly plates come off the stops exactly the same time the pump lever comes off its stop. (This is one of the critical items.) Be sure to use the rod to the pedal to move the linkage. Any side movement of the cross shaft will fool you. So will pushing on a side rod or the pump rod.

I have found that the pump lever was off it's stop when the butterfly plates were on theirs. Corrected so that they are all on stops and all are opening at the same time.

I also opted to leave the pertronix in since these either work or don't and I am certain that this is working, or the engine wouldn't run at all.

I did pull the dizzy and disassembled to oil the weights and springs and make sure nothing was left dry and that they moved smoothly.

When observing the timing at idle, I saw very little retarding of the timing due to lack of vacuum. I noticed that when the intakes "spit" or "spf" that the vacuum on the hose drops off and is not as strong. This is why I have timed it at with vacuum plugged in order that the higher revolutions (with no vacuum) will follow the timing curve and be on time.

I have called Chuck from Millersport to bail me out with the mixture. After talking with him, I should not have to adjust it if all was well before. Without a CO meter, I am just pi**ing in the wind.

I know I am much better off than when I first posted here and I am comfortable driving it to his shop - which I wasn't before. I will continue to follow up as problems are revealed.