decipering MAP log

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landychris
Posts: 17
Joined: Fri Aug 12, 2011 5:19 am
ECU Model: S80 Pro
Firmware Version: 54
Location: Gloucestershire
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decipering MAP log

Post by landychris »

Hi, it's been a while - it's good to see the same people still on here after all these years!

I've got a 6L GM based N/A V8 in a boat, which I'm having trouble with now it's had a propane conversion done. which is making me wonder whether to put my S80 onto it and run sequential and duel fuel - (ideally monofuel LPG).

It originally had the GM TBI system with a MEFI2 marine ECU with HEI dizzy.

I read the logs from the old MEFI system on petrol and with the following readings holding steady:
RPM: 3340
MAP: 68-69 kPa
Throttle angle: 40% (39.4-42.2)
Advance: 37.9 deg BTDC
Max poss RPM on super unleaded: 5600
Max poss RPM on regular: 5200

I had a propane conversion done, they put an Impco 300A mixer on there with a model E vaporiser.

Now the readings are as follows:
RPM: 3330
MAP: 75-78.4 kPa
Throttle angle 48%
Advance 37.2-37.6 deg
Max poss RPM on propane 4100

My interpretation of the differences are caused by the increased restriction from the mixer and associated fittings, but the reduction in max RPM and lack of power (big lack of power) is a concern. I can't work out whether it's just the restriction or also not enough fuel. It uses a wet exhaust system so can't put an o2 sensor on there

So, once I've sorted the above (or not) its leading me in the direction of swapping in my S80, 8-10 years ago it couldn't run LPG injectors, with the software updates (on V48 or similar atm) could it run LPG injectors directly without a piggypack ECU?
Alex DTA
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ECU Model: S40 Pro
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Re: decipering MAP log

Post by Alex DTA »

I think LPG injectors are low impedance, which the S80 cannot. It's a hardware limitation, not a software issue.
You *CAN* make them work with ballast resistors to increase the impedance, but it's not ideal.
If you do, you'll have to set the dead times correctly.
stevieturbo
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Location: Norn Iron

Re: decipering MAP log

Post by stevieturbo »

If you need to drive lowz injectors, there are various driver boxes you can use for this via teh ecu's highz output. They're old, I presume they're still available.

https://injector-rehab.com/product/aem- ... or-driver/

https://shop.vems.hu/catalog/lowz-exten ... p-161.html

http://www.jbperf.com/p&h_board/

Although when you say maximum rpm...why is this ? a power limitation or some sort of self imposed limit ?
stevieturbo
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Re: decipering MAP log

Post by stevieturbo »

And what is a "wet exhaust" system ? I'm sure water is not right at the exhaust port itself ?

For any tuning, really you need to be able to ascertain whether it is running correctly or not.
landychris
Posts: 17
Joined: Fri Aug 12, 2011 5:19 am
ECU Model: S80 Pro
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Location: Gloucestershire
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Re: decipering MAP log

Post by landychris »

Thanks, a "wet" exhaust is a marine exhaust manifold.

The headers are wrapped in a water jacket to reduce engine bay temps and reduce fire risk on a boat. The engine coolant is pulled in from the lake using a separate water pump, shoved into the engine coolant system like normal with a thermostat for the core bock, then the warm/hot coolant water (normally radiator inflow) outflows into the water jacket, which then mixes with the exhaust at the end of the manifold/riser.

So, to put an o2 sensor in there is very difficult without major surgery and (from the offshore racers) very unreliable as you can get a flow reversal with water mist and it screws the o2 sensor in short work.

(not my boat, but similar setup)
Image
landychris
Posts: 17
Joined: Fri Aug 12, 2011 5:19 am
ECU Model: S80 Pro
Firmware Version: 54
Location: Gloucestershire
Contact:

Re: decipering MAP log

Post by landychris »

The current MEFI2 ecu has a soft cut at 5600 and hard at 5800rpm and uses knock detection (albeit primitive) to retard the ignition as required (hence the different top RPM depending on the type of petrol I presume)

the max RPM is WOT that I've had / can do / could do under load.

This is the video, WOT on LPG maxing out at 4k, with no power at all, the change from 3k to 4k happens when the boat gets up on the plane and the load on the prop reduces

This is my boat take off (0-58kph in approx 11-12s)


This is not my boat, but this is what it used to be like (0-58kph in <6s)




So, going back to the original figures, the 8% higher throttle angle and 13% higher MAP reading for the same RPM and engine load condition - would that be air starvation?
Alex DTA
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Re: decipering MAP log

Post by Alex DTA »

landychris wrote: Wed Jul 07, 2021 3:43 amSo, going back to the original figures, the 8% higher throttle angle and 13% higher MAP reading for the same RPM and engine load condition - would that be air starvation?
Higher throttle angle at that percentage of throttle should equate to a higher MAP, so that looks roughly correct. If you had a higher throttle angle with the same or less MAP then you would have a restriction.
Ideally what you need to check is if you have the same MAP at the same throttle angle as before, that will show if you have a restriction.

If you don't have a restriction and you're making less power with a higher load request (not sure if you're Alpha-N or SD, but both are now higher) then either you don't have the right fuel mixture or the timing is retarded from where it needs to be.
katana
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Joined: Sun Jan 27, 2013 6:08 pm
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Re: decipering MAP log

Post by katana »

landychris wrote: Wed Jul 07, 2021 3:43 am So, going back to the original figures, the 8% higher throttle angle and 13% higher MAP reading for the same RPM and engine load condition - would that be air starvation?
Can't imagine it would be as Propane / LPG AFR's aren't that different to gasoline - just a bit richer I believe, so you'd have to really air restricted to cause that drop. Simple test, just remove the air filter and see what happens as that is usually a fair restriction on any intake! Isn't the octane rating on LPG higher so you can use more advance - have you?
stevieturbo
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Re: decipering MAP log

Post by stevieturbo »

Really you need some means of determining tuning if this thing has not been dyno tuned where you can ensure it is ok at least as a baseline.

Your lack of rpm could simply be low power, whether that's restriction or incorrect tuning is another matter.

As a priority I'd be wanting some means of mixture measurement. Also, that air filter looks tiny ( hopefully yours is not the same )

Or if you cannot get mixture measurements, you'd need to do some serious testing and plug checking ( ie lots of new plugs used )

But really, I'm sure there is some way to get an exhaust sample for mixture reading, or remove the engine and have it tuned with both systems or LPG injection on thge dyno.

As for the LPG....as most car systems just mirror the petrol ecu, you could take that approach. Albeit the petrol ecu is just the DTA but the LPG piggy backs, that way you'd have no injector control issues and you could still do dual fuel.
landychris
Posts: 17
Joined: Fri Aug 12, 2011 5:19 am
ECU Model: S80 Pro
Firmware Version: 54
Location: Gloucestershire
Contact:

Re: decipering MAP log

Post by landychris »

That was my thinking, getting a MSD cam trigger that replaces the dizzy so the S80 controls everything then piggy back using a standard LPG ecu thing.

Boats tend to run without a filter, the thing you can see is a flame arrester so its basically a metal gauze "filter"

The airflow to the engine in a boat (like mine) is relatively "pure" i.e. not used in multiple dusty / wet / humid etc places,. just on a lake and under cover so a pretty controlled environment
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