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thechief68
Samba Member
Joined: May 25, 2012
Posts: 29
Location: Vancouver
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 Posted: Fri May 17, 2019 5:04 pm Post subject: ECU swap 77 automatic with 78 automatic |
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Is there any risk swapping out the ECU from a 77 automatic with a 78 automatic?
My baby is the 77 and my donor bus is the 78. For my years, the wires on my coil were swapped (figured this out the hard way after burning out a Petronix electronic points)... and it would start and run perfectly fine... for a while. But on more than one occasion the engine would just cut out leaving me stranded and hitch hiking back to town...
I corrected the coil wiring but am now concerned that the wrong side of the coil attached to my CPU may have cause some components stress/wear as my engine has a persistent misfire and my 2.0 litre was rebuilt about a year ago.
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1977 & 78 Westfalia
2.0L Automatic |
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SGKent 
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Fri May 17, 2019 5:18 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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Petronix does not provide the proper wave form for the ECU to work right. The waveform from the coil is the baseline signal to the ECU that forms the injector pulse.
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SamboSamba22
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Joined: August 06, 2015
Posts: 2772
Location: Benton, Arkansas
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Fri May 17, 2019 5:36 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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| SamboSamba22 wrote: |
As far as I know, as long as the 77 bus is Federal bus model, as well as the 78 donor bus, and not intermixing Federal/California Emissions or vice versa, you’ll be fine.
Don’t quote me but I believe on Ratwell it states the ECU’s are the same for like 76 (Bus) to 83 (Vanagon). |
the 77 and 78 ECU are the same. He cannot use Pertronix with an ECU and know it will run right all the time under all conditions. Period and end of subject. If you write Pertronix and tell them you have a L-jet FI T4 engine they will tell you their system only works with carbs. The 1979 California system with electronic ignition used a completely different arrangement in case someone wonders about that.
For the curious:
The coil produces a waveform when the points open and close. The capacitor buffers that waveform.
The ECU gets that signal (waveform) and uses it to shape the length of the initial injector pulse.
It adds length for temperature on TS2
It adds length for temperature on TS1 in AFM
It adds length for vane position in AFM
It adds length when the AFM vane is quickly swinging open (assumes acceleration)
In 1979 O2 model it adds length when lean
It never subtracts from the baseline pulse
This combination makes the mixture that fuels the engine by length the injectors are held open. Longer time open = more fuel. If the baseline pulse is improper the engine will not get the correct mixture.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50352
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| Posted: Fri May 17, 2019 6:44 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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| I think the main difference in the various 7 pin Federal units is in the factory settings of the wiper and spring. I believe the components themselves are the same. |
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Gregg in the 603
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Joined: April 13, 2013
Posts: 404
Location: New Hampshire, USA
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| Posted: Fri May 17, 2019 7:20 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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Steve, no Pertronix with FI? I know it has its fans and its detractors, but I had no idea in all my years on here that it does not work well with LJet.
Still learning, thanks
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1979 Mexico Beige Westy auto
Dirty Dover, NH |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50352
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| Posted: Fri May 17, 2019 7:33 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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| Gregg in the 603 wrote: |
Steve, no Pertronix with FI? I know it has its fans and its detractors, but I had no idea in all my years on here that it does not work well with LJet.
Still learning, thanks |
Assuming the Petronix doesn't play well with the FI, I would guess that adding a capacitor of the correct size would make it work fine. Maybe buy a handful of capacitors starting at about 0.05 microfarad and keep going larger until the problem disappears. |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Fri May 17, 2019 9:41 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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| Gregg in the 603 wrote: |
Steve, no Pertronix with FI? I know it has its fans and its detractors, but I had no idea in all my years on here that it does not work well with LJet.
Still learning, thanks |
It may work and one day not. If you read threads where people have had issues., or asked Pertronix about it they specifically say it is only for a carbed T4 engine. Example from a 20 second search:
https://shoptalkforums.com/viewtopic.php?t=146669
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| I emailed Pertronix with my concerns and just had to call after I received my response. The folks at Pertronix advised me that they in fact "do not manufacture a distributor for my vehicle". They also advised to "not" try and convert ... with their kit either. That is unless I want to dump the fuel injection system for a carb(s). They say that the Pertronix Control Unit will not interface with the fuel injection system ... |
The problem is that the coil and points produce an electronic waveform that the ECU is looking for to establish the injector pulse and timing. An electronic ignition gives a different waveform. When the ECU can no longer work with the pulse from the Pertronix it will stop sending the correct signal to the injectors.
This is what I mean by wave form. One from an electronic ignition is quite different. https://www.forabodiesonly.com/mopar/attachments/scope-jpg.1715100610/
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cmonSTART
Samba Member
Joined: July 15, 2014
Posts: 1915
Location: NH
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| Posted: Sat May 18, 2019 4:39 am Post subject: Re: ECU swap 77 automatic with 78 automatic |
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I hear about this all the time, but I have run a Pertronix ignition for years with no issues (that I know of..) The bus runs great with it. Who has had an issue with it?
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'78 Bus 2.0FI
de K1IGS |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Sat May 18, 2019 9:46 am Post subject: Re: ECU swap 77 automatic with 78 automatic |
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| cmonSTART wrote: |
| I hear about this all the time, but I have run a Pertronix ignition for years with no issues (that I know of..) The bus runs great with it. Who has had an issue with it? |
with FI apparently Pertronix customer support who got tired of the calls.
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thechief68
Samba Member
Joined: May 25, 2012
Posts: 29
Location: Vancouver
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| Posted: Sat May 18, 2019 4:26 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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Thanks for all your insights everyone... I changed to electronic points because I was having issues with mechanical points (that’s when the “engine cutouts” started) but this may have been related the my mis-wires coil... on that topic, whenever I he engine would die, I would swap out points and condensers and coils on the side of the road with varying results. In fact, one time I just had to park it where it died for several hours and when I returned, it fired up without changing or adjusting anything suggestions it could be a thermal problem.
I have a set of points and a condenser that I can swap in. I actually have a spare distributor and I can set up on the bench and then adjust dwell once it’s in the van.
Any rules/ guidance on swapping out a distributor? Also the current distributor feels like it has more play (both vertically and “rotationally”) than I think it should... how “tight” should the shaft be and how difficult is it to adjust/rebuild?
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1977 & 78 Westfalia
2.0L Automatic |
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SGKent
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Sat May 18, 2019 4:36 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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always make sure that the dist lobes have a special distributor grease on them ot the rubbing block will wear and break. Also make sure that the connector on the end of the wire doesn't have a broken wire inside the jacket right at the crimp. A bad ignition switch can cause the engine to die like that too intermittently.
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Wildthings
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Joined: March 13, 2005
Posts: 50352
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| Posted: Sat May 18, 2019 5:32 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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| Excess axial movement in the shaft can cause the timing to dance around. I would guess that an axial play of around 0.020" would be ideal, but have never seen a spec. |
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thechief68
Samba Member
Joined: May 25, 2012
Posts: 29
Location: Vancouver
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| Posted: Mon May 20, 2019 2:09 pm Post subject: Re: ECU swap 77 automatic with 78 automatic |
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So I cleaned/lubricated this guy and set it up on the bench... way easier than working on it installed in the engine... I will do the same with my spare. Going to fire it up shortly...
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1977 & 78 Westfalia
2.0L Automatic |
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