Diesel EFI vs Gas EFI

[PapaG]

What makes a Diesel EFI system more complex (accurate) than a Gas-Petrol EFI? I have been told that a gas EFI system doesn't provide the Accuracy required for a Diesel EFI.

I just don't see it.

Thanks
Richard

 

[ivymike]

Huh? the gasoline version shoots a particular quantity of fuel into the intake manifold each engine cycle (or couple of cycles), but has no important timing constraints. The diesel version shoots a particular quantity of fuel into the cylinder at very high pressure over a very narrowly defined period of time (or more often, over several narrow time windows each cycle).

 

[JDana]

In the diesel the ignition timing is set by the fuel injection. Needs to be precise(or more) as the spark in a gasoline engine.

 

[PapaG]

I didnt make that clear.I am talking about the ECU. The Injectors would be in the same position in the head as before. IDI injection system with mechnical injection adapted to electronic. Aftermarket ECU's would be easy to use for this setup if the would work.

VW 4 cylinder IDI system like on older 1.6 NA or TD, 1.9 or 1.9 TD NOT TDI.

I could use Spark signal or Injection signal. Crank Trigger.
to fire the newer electronic injectors. The old style injectors hit a bushing that has a hole in it for the IDI type setup. This is a removable bushing.

The IDI bushing could be left out or remain in the system

 

[PapaG]

Pre chamber bushing pics

I will have to look for a TDI head if someone need it.

 

[PapaG]

TDI uses a sensor on # 3 injector for timing, = boost sensor, MAF, and normal GAS type sensors.

Fuel pressure not a problem. It is getting harder and harder to find good parts for thhese older diesels. Fuel Injection Pump are getting wore out that the good pump cores are hard to find. Junk yard stuff, if out there but who knows the condition of the pumps.TDI uses a sensor on # 3 injector for timing, = boost sensor, MAF, and normal GAS type sensors.

Fuel pressure not a problem. It is getting harder and harder to find good parts for thhese older diesels. Fuel Injection Pump are getting wore out that the good pump cores are hard to find. Junk yard stuff if out there but who knows the condition of the pumps.

 

[KiwiME]

Perhaps a proper aftermarket sequential injection ECU could work if the injector driver electrical output matched the characteristic required for the diesel injector. However I think a common-rail type injector is quite a different animal (electrically) than a gasoline injector.

Speaking of gasoline injection timing, the old Bosch CI (continous injection) just sprayed all the time into the ports. My Motronic II-equipped old BMW only has two sets of pulses 180 deg out of phase to fire 6 injectors.

Could you not use a VP37 pump off a TDI?

 

[PapaG]

I don't know. I think they both use the same too to lock the pump timing in place when doing some work on the engine, like replacing the head. I will have to check it out.

It is pre CRD, the pumps supply high pressure to the injecors. From whit I have heard A TDI pump can be converted to a pure Mechanical pump to elemate the electronics. I will look into it.

I have CIS car 1.8l and a 92 Golf GTI Motronic car 2.0l 16v with a TT chip, TT cams, Borla exhaust.

After market FI syster could use SDS, PerfectPower or someother system. Crank trigger could be used in place of gas distribitor. I am not sure what I could use a a cam sensor.
Richard

 

[KiwiME]

Re: the VP37, I'm sure you know all this but just in case:

I think the injection quantity actuator simply moves proportional to electrical current, and there is a positional feedback sensor. The circuit required to drive that (in a position control loop) would be a piece of cake to design and build.

The VP37 start-of-injection (timing) is a PWM (pulse-width-modulated) signal based on feedback from the #3 injector and crank position sensor. A more complicated circuit to design, although it's possible you could also just modify this back to the all-mechanical rpm/pressure hydraulic system used in the original pump.

Assuming no turbo, all you need to do is direct those two signals from the "gas" pedal potentiometer, no ECU required. I'm not sure if there is any off the shelf item that would do this for you - a TDI ECU would be also looking for pressure and mass air flow signals.

Hope I haven't gotten off track!

 

[PapaG]

It would be TD based. Most aftermarked FI uses PWM to control fuel delivery. I have built and Installed several Megsquirt (dyi) EFI units. These are not suitable because they are batch fire injection. Like a the old style VW Type3-4 ystem and 914
system,Djet, Ljet plus tons of euro cars.

Richard

 

[KiwiME]

I had a look at the MegaSquirt site since I've never seen it before.

It does seem that it is not suitable for a diesel. Aside from the batch injection and doubtful timing accuracy it doesn't seem to be of any particular use if no O2 sensor or fuel map is needed.

Not sure exactly what your desired engine configuration or what your goals are but in a practical sense either use a complete TDI engine w/ECU to replace the TD unit, or continue with the mechanical distributor pump. I'm not clear on why the parts are hard to come by - the 3rd world country where I live (New Zealand) has probably 300,000+ old diesel vans, SUV's and trucks that are on the road and considered serviceable. The average fleet age is 12 years!

Anyway, good luck with your endeavor!

-Paul

 

[PapaG]

Paul etal:

The megasquirt is fine for gasoling setups that can use a batch system. It can be run with out some of those sensors but it doesn't matter as we are talking a diesel. I have used the megasquirt on several Gasoline(petrol) engines.

While I am sure their are tons of used parts, but the USA didn't actually didn't see as many diesels. I am not sure why. I bought a new Rabbit(golf) diesel in 81. The big complaint by my self and others on several diesel forums and lists are good cores, and used parts too. A lot of the older diesels were run to death, poorly matinained by people and shops that didn't kmow how to work on small diesels. Large Diesel shop could have worked on the Golf type diesels but the price per hour for labor was quite a bit higher.

This is just a attempt on my part to help use some newer, more readly available parts on the older VW diesels. I have wondered about this for sometime, but it seems to be a untried or tested modification. It also may not be cost effective too.

I wanted to see what some other people not directly tied into the older VW diesels might have to say about this idea and feasibility of such a project. Too many nay sayers in this the VW diesel area, but they have been proved wrong in some other projects.

I don't want to get some kind of recognition on this other than a pat on the back.

Thanks All

Richard
New Ulm
Texas, USA

 

[Rob45]

Richard:
I think you can answer your own question, since you wqrote:
"the USA didn't actually didn't see as many diesels. I am not sure why. I bought a new Rabbit(golf) diesel in 81."

LOL!
Look at what GM was doing with Diesels in those days, and how this tarnished the reputation of Diesels generally; the VW Diesel with its noise and miserable performance did nothing to make things better!

Key to your question is the increased complexity required to get both fuel timing and quantity exactly right for the diesel - the gas engine really only cares about the amount of fuel; timing is much less critical, and if you were to get the timing of injection 180 degrees off, the engine will still run fine. J. Lucas and Co. demonstrated this a number of years ago.

 

[PapaG]

Rob:

It is Probably a exercise in futility. I am one of those people that think there must be a way to do something. I hate to let some thing "beat me".

I have a diesel & automotive back ground as a Pontiac-GMC dealer mechanic, and then moving on to the big trucks. But when I almost starved in the 80's. I had to find something that was oil proof in Houston. SO computers I go.

Some folks say I am a little anal (a lot) in computer work. I just wont let it win.

Richard

PS: I have one of those bad olds 5.7 diesels, that has gone over 400k miles. Time for a rebuild, if I can find parts for it. People didn't know how to drive one of those, or maintain them. It was not a gas engine, thats all they knew how to drive. I can get 30mpgs out of it, on the highway. It has been in 4 differnt cars and lastly a truck.
~R

 

[PapaG]

The new Cummins engines in the Dodge trucks use a multi-squirt (pilot) injetion to quiet them down. The new "design" had to pass the "Wendys" test. That is where you can go to a fast food place, and order at the drive though and NOT have to shut the truck off. They could have made it quiter, but people wanted a diesel sound.
Go Figure?

I will still brain storm on this when I can not sleep. All he points here are good ones, and make sence.

hanks for all the input folks.

Richard Green
PS any one want to keep throwing their ideas around are more than welcome to.
~R

 

[mattsooty]

Multishot injection is not a particularly new technology in the modern DI Diesel engine. These engines can usually delievr between 2 & 5 injection events per cycle - the reasons for which are out of the scope of this thread.

However, that 'diesel sound' coming from the engine usually comes at the expense of monstrous NOx emissions.

MS

 

[PapaG]

MS
You are correct, except it shows something that can be done with a diesel EFI. That was my point, but as usual I get ahead of my typing, as compaired to what I am thinking *>)And that is rereading my post before posting

I think the cummings uses 5.

Thanks MS for your input.
Richard

 

[PapaG]

Not that I am looking to do multishot injection.

Richard