348 air fuel adjustment

You deserve congratulations, not crucification. The baseline adjustment of 383 ohms is just that-- a baseline. It's like backing the idle mixture screws on a carb out 2 1/2 turns after a rebuild. Neither adjustment means that the fuel mixture is set correctly, or even the same between the two banks, it just means that the engine should run when you turn the key so that you can warm it up and set the mixture correctly. The correct way to adjust the mixture is by exhaust gas analysis, but what you did is better than simply setting both the MAFs at 383 ohms and walking away.

Suggestion: if you don't have any way of checking the mixture at least read the plugs and make sure that the mixture is not too lean. Better too rich than too lean-- while an engine makes its best power on the ragged edge of lean it's possible to burn valves or pistons if you're not careful.

 

Mike is absolutely right, it is like tuning two separate engines. One bank can have a slightly different values from the MAF, CTS and O2 sensors so it is normal that the mixture screw (pot) setings are different to achieve the same mixture on both banks. As I mentioned before, the pot on the MAF is not tuning the MAF but it is tuning the ECU given the existing values from the MAF, CTS and O2 sensors.

On my 348, I will be installing converted 355 exhaust ECU-s which will each have a digital display showing the amplified voltages from the left and right Thermocouples and, indirectly, the EGT-s of the banks. Then I will use these to equalize the EGT-s via the pots on the MAF-s.

Regarding the max power, I thought it was when the mixture is a bit on the rich side, at about 13:1 AFR?

 

So true ^^^^

I run wide bands with fully adjustable fuel rails and ecu's. Both side do not run the same. Took some work but I'm getting closer. My motor right side need a couple more psi on the fuel rail to run equal AFR side to side. When you get them exactly even it runs great, dial the afr to 12.5-13 and you will fly

 

Yes, one more factor that I missed to include together with the sensor signals - the fuel pressure. With the fixed factory pressure regulators, there could also be slight difference in fuel pressure left and right as the regulators are not perfect. This can also be compensated for by the pots on the MAF-s.

I tend to think that reason why the ECU trimming pots on the MAF-s are necessary for the 348 engine concept is the fact that you have two engines, next to each other, which you have to make running at the same mixture, i.e. to synchronise them. In this case, it is highly unlikely that the left and right pots would be at exactly the same value (resistance) when the mistures (AFR-s or EGT-s), left & right, are made the same. Whe we are setting the two pots at exactly the same resistance, we are probably de-synchronising the banks.

 

Agreed, Miroljub, but even if we only had four cylinders and a single MAF the adjustment screw would still be useful for achieving an optimal AFR.

Interesting stuff from Tim regarding the need for disparate fuel pressures to balance the two banks. Seems surprising to me but I believe it because Tim knows what he's doing.

Tim, I wish you'd do a write-up on your adjustable FPR setup to help save time for those of us who'd like to follow a similar path.

 

BTW, Miro, I mispoke somewhat earlier when I wrote that engines are most powerful on the ragged edge of lean. What I should have said is that they're most efficient there, but of course you and Tim are correct about AFRs for power. I'm not sure how much the MAF adjustment screws affect the mixture under acceleration and heavy loads but I was assuming when I wrote the above that adjusting the MAFs doesn't have a huge effect on the mixture at WOT. In that case it'd be fine to tune for a leanish mixture under constant load as long as the mixture was rich enough for max power under acceleration. But since I haven't gotten to the point of experimenting with the AFR curves in my car I'll gladly defer to Tim and his experience.

 

The fact is that, by turning the pot, we are not adjusting the MAF in any way but adjusting something in the ECU via its pin 43 (the variable resistance of the pot is between ECU-s pin 43 and the ground; pin 6 of the MAF is not connected to anything in the MAF and pin 1 is common ground). So, we can forget about the MAF. The question is whether the varying resistance between the ECU's pin 43 and the ground affects (trims) the whole of the fuelling curve or only its "idle" and perhaps its "part throttle" (PT) sections. I believe Tim can advise on this if he can observe whether there are any differences in AFR during PT and at WOT at different pot resistance settings. A Wide Band with a data logger would be ideal for this experiment.

 

Those pots I understand only help set idle afr. Before I could get them to make any difference I changed all the intake gaskets, rebuilt TBs and messed with the throttle linkage over and over until I got it synced using the WB sensors, then I moved on to tuning fuel pressure.

The ecus just plan suck and are very very slow to react and control the mixture, you can see it oscillate with the WB. Not steady like a modern ecu

Far as the regulators they are off the shelf parts, some I had some ordered. I went to AN fittings after using a M to AN adapter. very simple to do. This made the biggest difference

For most efficient power yes you want all 8 cyls to be working close to the same as possible. Not there yet but getting closer


FPR
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Now that you mention it I recall this being my experience on other cars. Not sure if the adjustment has any effect at all on higher RPM/load condition but based on my terrible memory the screws function more like idle mixture screws on a carb instead of an overall mixture adjustment. Which makes sense now that Miroljub has pointed out that the potentiometers are connected to the ECUs, so they're presumably not modifying the MAF signal as a whole.

Thanks for the info. I didn't think it'd be that easy for some reason. Now that I have better recollection of the purpose of the adjustment screws on the MAFs the usefulness of adjustable FPRs is even more obvious.

Good discussion. Thanks to you and Miroljub for rattle the old memory bank. I swear if I don't use a bit of info on a regular basis it gets really dusty really quickly.

 

BTW, Tim, I see the metric adapter on the input side of the regulator. Is the 90 degree fitting to the return line also an adapter or are the original return lines AN (or did you replace both return lines entirely using metric adapters on the far ends)?

 

Interesting discussion .... good to hear the engine running was improved with the described MAF adjustments ..... ernie improved running a bit with changing the thermostat .... the 348 is not as 'thermostat sensitive' as the 355 ... but if coolant temps are a bit low during highway driving .... it may be worth changing it ...

 

great info.

don't own a 348 but I've heard of the AFR adjustability with the 348.
as the OP referenced by adjusting the A/F screws etc.

is this adjustment possible on either the 2.7/5.2 355's ?

I would think maybe for the 2.7 and most likely not on a 5.2.

 

Tell me about it

I'm a old pollack

I need re training to use the elevator LOL


At this point in life I prefer selective memory so when I do things over its a new experience LOL

 

LOL I dont remember LOL

I think I just put an AN fitting on that return line and used the stock hose

I'll try to look at my jegs account but I order like 10 of everything when I order stuff just to have them in stock

 

No big deal. I'll figure it out. Just thought it'd save some time if you happened to remember what you did. Thanks for the overview though, it's helpful.

Happy New Year, BTW.

 

Tommy, it appears as though Tim used Aeromotive 13129 regulators in his conversion: https://www.aeromotiveinc.com/product/efi-bypass-regulator/

From his posts above he does not recall the specific fittings used but you can see the metric adapter on the input side in his pic above. Hopefully the next person who does this conversion will post a parts list here but for now we'll have to figure out the fitting sizes for ourselves using Tim's pic to show us what the final configuration should look like.

If your '89 is a 2.7 car I suspect Tim can help you with chips as he has advertised a set in the classifieds before. I have no idea if he's developed anything for 2.5 cars.

 

There were other discussion, some time ago, on the CO Pot adjustment here: http://www.ferrarichat.com/forum/348-355-sponsored-bradan/201174-how-maf-co-screw-does-not-matter-closed-loop-operation.html and here: http://www.ferrarichat.com/forum/348-355-sponsored-bradan/204039-wrong-maf-co-settings-motronic-2-5-car-can-cause-fires.html?nojs=1#links

 

Yes I used the areo regulater

Here are some or all of the fittings I ordered from summit, think these are them I had a big order. You may need to double check them

AEI-15606 FITTING-`Oring fitting for FR

RUS-670520 METRIC ADAPT #6 X14MM 1.5` rail adapter AN to metric

SUM-220687 -06 90 HOSE END SWIVEL`return line to AN fitting

 

Thanks much, Tim!

 

Thank you for the links, Miroljub. I had not seen either one before.

Do you happen to know the differences between 2.5 and 2.7? I've never bothered considering it since my car is 2.7 but now I'm curious since these discussions regard 2.5. Apparently the TPS on 2.5 cars is only 3 position instead of continuously variable but I'm wondering if there are other differences from an engine management (as opposed to installation) perspective.

 

If I can get a dump file of the 2.5 I may be able to do something