manual how to adjust the 3.5 engine (ignition and A/F ratio)

[vandor]

MPS = manifold pressure sensor?
Where is it located?
Thanks,

Csaba

[werminghausen]

You adjust fuel pressure at the damper between intake manifold and firewall. There is a set screw..not sure maybe 10mm or 13mm.
You measure fuel pressure with a gauge: disconnect the cold start injector fuel line and install pressure gauge...then adjust with fuel pump running. No hijacking.

[werminghausen]

Originally Posted by vandor

MPS = manifold pressure sensor?
Where is it located?
Thanks,

Csaba

MAPS is the pot located at the firewall right behind the intake manifold with the vacuum connection (rubber line) to the manifold and a wide el. connector. I have never touched it but i am ready to tweak it for the purpose of correct
A/F ratio.

[WANT '71 280SEL]

Informative thread, thanks Martin and Graham!

Everyone should note, as Graham pointed out, you need to first make sure you don't have vacuum leaks as everything then goes out the window.

Best Regards,

David

[WANT '71 280SEL]

I'm attaching the write-up Graham did awhile back on adjusting and cleaning the TPS.

Best Regards,

David

[werminghausen]

Thanks so much Graham,
Yes I moved with this car from Boston to Muscat Oman... it is still an US car.
I understand pretty much what you are saying.
Ignition timing is clear now.
AFR: I'll try and weld the bung before the first muffler...I hate crawling under this car and weld there.. is it a drag to get the exhaust pipe out? Yes I guess.

Not sure of the LM-2 shows AFR or something else...
I believe I can leave it in during driving ... that was the reason I bought this one.
I'll start fooling around. I will try and get 13 at idle... 13.5 -14 for steady cruise (not beyond 14.5 because of burning valves) and 9-11 at acceleration...would you agree?
Someone mentioned before that instead of messing with the MAPS I should regulate AFR with the fuel pressure. What about this idea?
Too bad that you are leaving... Hope I can get a hold of you in between.
Safe travels, Martin

Originally Posted by Graham

So you have US spec car but you are in Oman! The USA specs do say at idle you should be at 6deg ATDC with vacuum. Maybe stay with that at least initially. Make sure you have A/C off. Later you can try more advance.

What fuel does your owner's manual specify? If your fuel in Oman is lower octane, then it would probably be just as well to be on the low end of the 3000rpm advance range. Manual says this can be 30-38deg BTDC, so perhaps 30 would still be good?

Check you manifold vacuum - should be about 15-17" HG at idle. Very important not to have vacuum leaks.

You can get cheap rev counters. But maybe a Digital timing lights with rpm? or a multimeter with tach?.

Even with tach on my car, it is not easy to check at 3000rpm (need two people) I usually set timing at idle (800rpm for your car) first. Then rev car and check at 1500 and then a burst and see where it goes to at 3000rpm. If distributor centrifugal advance is working, according to the specs, your car with vac connected should go from 6ATDC to +/-1TDC at 1500rpm and then to 30-38BTDC at 3000rpm. But they also say vacuum adjustment after retard is 12-18deg retard at idle. That I don't understand. It makes sense on my 1972 (figure below yours in manual), because the vacuum causes the timing at idle to retard by 10-14deg. Take vac off when at 5 ATDC, and it advances to say 5-8 BTDC. But on 116, those numbers don't jive. So I would set at 6ATDC at 800rpm, then rev up and see where timing goes at 1500rpm and at 3000rpm.

Re fuel pressure - 29psi is per spec. 2.2 bar is about 32psig. Car will run richer but still OK if mixtures have not been messed with.

Re Innovate Motorsports LM-2 A/F - That would be great! I have an AEM AFR permanently installed. I put the bung on one side just before the first muffler and after the crossover pipe. Not 100%, but should be OK. Seeing your connection is temporary, you could put one on each side!

Re ECU idle mixture. First make sure throttle position switch is set to signal ECU that engine is at idle.(There is a write up I did on TPS adjustment here somewhere). Set knob on ECU in centre of it's range. 9 clicks from either side, I think!) With warmed up engine, check %CO or AFR on meter. At first adjust by ear until engine sounds OK, then fine tune. %CO should be about 2% (AFR 13.8) but I find that having it richer helps with hot starts. I am at about 4% (AFR 13) Rev car in between and do it a few times and let meter settle out.

For load conditions, you need to adjust MPS. You do it with a 4mm allen wrench - There is an adjustment on one end of MPS. Sometimes it is sealed with wax? if never adjusted.

If you can drive with the meter connected, you can check on say a steep hill (in Oman?) or maybe with brakes partly on and engine loaded up. %CO should be in 2-5% range. (13.7-12.64). If you can't drive with meter, after setting up idle mixture, pull the plug off the Throttle Posn sw. Then adjust MPS so you get about 1% at say 1000rpm. Rev car in between and do it a few times and let meter settle out.

Sorry for the information overload. I am leaving soon for 2 month trip and won't have my books with me, so just wrote down everything that came to mind!

Good Luck with it!

[Graham]

Originally Posted by werminghausen

Not sure of the LM-2 shows AFR or something else...

Hi Martin,

The LM-2 will read out Lambda and AFR. I think you choose one or the other in setup menu. I was once going to buy one, but chose built-in AEM instead. BTW, Lambda for gasoline, is just AFR/14.7.

When I start up cold, the AFR will be low and will gradually head up to about 12.5-13 at idle. Same under way, it will be around 10 and then increase to around 13. With light throttle, it varies between 13.5 and 14. After a typical hot start, AFR may peg out at 18 showing the reason for difficult start (too lean) and then it will decrease back to 14 or so as you drive. If you floor it, AFR will drop, but not to 9. maybe 11.

Fuel pressure does affect AFR because more fuel flows through injectors when rail pressure is higher. But the Fuel Pressure Regulator adjustment is quite sensitive. I would first set the fuel pressure at say 32psig. Then adjust MPS in very small increments (1/8 turn at a time) to achieve desired AFR.

I will still be on-line while travelling, just won't have my car reference files & books with me!

[werminghausen]

Great!
Thanks so much Graham. I think I understand and will start as soon as I have the rotor for distributor. I took the distributor apart and tweaked some parts as It had too much play. Now it is much better (I had trouble to adjust the dwell because of too much play).
I'll see if I can hook up the LM-2, then report back.
Martin

[Graham]

Originally Posted by werminghausen

Great!
Thanks so much Graham. I think I understand and will start as soon as I have the rotor for distributor. I took the distributor apart and tweaked some parts as It had too much play. Now it is much better (I had trouble to adjust the dwell because of too much play).
I'll see if I can hook up the LM-2, then report back.
Martin

One thing I saw here about welding the bung. I. Think it was barri (gurunutkins) who welded the bung to a saddle that fitted over the outside of the exhaust pipe. He then clamped the saddle to the pipe after making a suitably sized hole for the sensor.

[werminghausen]

I'll weld tonight the bung into the right side pipe right after the last muffler..before the stainless cover starts.
I need to get the cigarette lighter going...not sure why this thing has no power (for LM-2 power)
Then I need to get the fuel pressure gauge installed for adjustment..
Is it good to have the gauge inside the car for observation while testdriving?
I mean does fuel pressure change during driving conditions? or is it pretty stable?
MAPS: My sensor has still the cover on the one end...also it looks like there is a another cover underneath the wax thing. ...I don't see the Allen head screw.
Would you rip this thing open and dig down?
Alternatively I have a spare MAPS unit in a box...with the screw open as you show it. (the end looks slightly different if I compare the two). Are there different units around and are these interchangeable?
I can send picture of the two later today.

Thanks, Martin

[Graham]

Originally Posted by werminghausen

Then I need to get the fuel pressure gauge installed for adjustment..
Is it good to have the gauge inside the car for observation while testdriving?

No need to have it inside car. I put mine there so I could check leakdown of pressure after stops. But now it stays pretty steady.

MAPS: Are there different units around and are these interchangeable?
I can send picture of the two later today.

Thanks, Martin

I haven't seen different ones, but did read somewhere that some had a different head on adjustment screw. Pictures would be good!

[werminghausen]

Hi Graham

I welded the bung into exhaust for the LM-2 sensor. See pics.

I took also pics of the 2 MAP sensors I have...One installed and the other on the shelf.
Which one would you use?

Martin

[Mike D]

Martin, I think you would be better off installing the O2 before the muffler. You're liable to get all kinds of wacky readings back at the very end of the exhaust system.

[Graham]

Originally Posted by werminghausen

Hi Graham

I welded the bung into exhaust for the LM-2 sensor. See pics.

I took also pics of the 2 MAP sensors I have...One installed and the other on the shelf.
Which one would you use?

Martin

The MPS with the wax like material likely has the allen hex adjustment under the goop! No harm in picking out that material, but that MPS has not been messed with so should be set correctly if teh fuel pressure is set at factory 2bar. But we know 2bar can cause hot start problems with modern fuels. Maybe mess with the adjustable MPS for a start?

I agree with Mike about the O2 sensor location. When I suggested before first muffler, I meant first one starting from engine! Problem with having it near tailpipe, is that you can get back mixing of air from teh other open pipe. I tried that initially and had to stuff a rag in the other pipe to get more reliable readings.

Here is a pic of mine (for easier temporary attachment, it could be on outboard side.)

[werminghausen]

Did you stuff a rag in the pipe of the sensor or the other one?
No excuses.. I knew that it is not 'correct' when I did it.. I was lazy, didn't want to mess with R&R the muffler... too bad.
I'll try to deal with it. I'll try it out.
Any more suggestion in order to get better readings?

I'll try to use the other MAPS.