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> FI system troubleshooting, Two FI components will not work
Such914
post Jun 20 2018, 07:58 PM
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Hello, my mechanic is finishing up a rebuild of my cars FI system, and we cannot get it to work. We have some parts we know are broken, but replacements haven’t worked either. Are there any known sources for these?

-Manifold Pressure sensor (known as the 'grenade')
-Air bypass valve

The issue that we are experiencing is misfiring and lack of power in the top end. Apparently they have tried 3 sensors to no avail. It is a ‘74 2.0.

Thank you!
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914werke
post Jun 20 2018, 09:43 PM
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76-914
post Jun 20 2018, 09:56 PM
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You can disconnect everything, except the MPS, and it will run. Repair kits are available thru Tangerine Racing. I don't remember the name of this do dad but it is like a volume control so you can adjust the ohm output. Unplug the head temp sensor and plug that in place and turn it to the value needed for cold engine. I can't remember that value either(I'm running a Subaru engine (IMG:style_emoticons/default/happy11.gif) ) Maybe 350 ohms (IMG:style_emoticons/default/confused24.gif) Or if you are sure everything else is OK just rotate the dial until it starts. You did verify that the CHT sender is good, correct?
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Rand
post Jun 20 2018, 10:19 PM
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QUOTE
-Manifold Pressure sensor (known as the 'grenade')
-Air bypass valve

Those things will mess with your fuel / air ratio. But if you are experiencing misfiring, I'd look first at components related to spark, not fuel.
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TheCabinetmaker
post Jun 21 2018, 08:14 AM
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Adjust valves, adjust dwell, adjust timing. In that order. I agree with Rand. Sounds like spark,timing, dwell adjustment, Etc. Adjust timing with distributor vacuum unplugged and capped
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rhodyguy
post Jun 21 2018, 08:30 AM
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FI harness, trigger points? What exactly happens? High idle, low idle or just refuses to start and run? The components need to be matched properly.
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TheCabinetmaker
post Jun 21 2018, 09:43 AM
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Go here. Read thoroughly, then test items as outlined. It's all pretty simple really. How do you know you have broken parts? Did you test the parts? No offense to your mech, but does he really know these cars and the injection system? You would not believe how many mechanics just "think"they know 914s.

https://members.rennlist.com/pbanders/DJetParts.htm
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Such914
post Jun 25 2018, 10:43 AM
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Thank you all for all of this awesome information. Sorry about the slow reply, but I’m sending this information over to my mechanic. Hopefully we can get this moving! He’s worked on a lot of 914’s before, but I think this information is pointing us in a good direction. This FI system has been a lot more troubling than I anticipated!
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Mblizzard
post Jun 25 2018, 10:55 AM
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Is this L-Jet or D-Jet?
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914Sixer
post Jun 25 2018, 10:58 AM
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My main concern is the wiring harness. They are old and brittle. Lots have high joints in them. This causes problems to come and go. Bad parts are labeled because of this. The FI system has to see each part of the system.
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Jazzy
post Jun 25 2018, 12:06 PM
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QUOTE(Mblizzard @ Jun 25 2018, 06:55 PM) *

Is this L-Jet or D-Jet?

2.0 and 1.7 are always D-jet, only 914 with L-jet is the 1.8.
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Mblizzard
post Jun 25 2018, 12:30 PM
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QUOTE(Jazzy @ Jun 25 2018, 10:06 AM) *

QUOTE(Mblizzard @ Jun 25 2018, 06:55 PM) *

Is this L-Jet or D-Jet?

2.0 and 1.7 are always D-jet, only 914 with L-jet is the 1.8.


Yes. I missed the 2.0 in the original post! (IMG:style_emoticons/default/headbang.gif)
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dr914@autoatlanta.com
post Jun 25 2018, 12:31 PM
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those are not the problem, I would say that. your distributor is the problem, trigger points or ignition points. A bad pressure sensor gives great top end power, an open aux air valve just causes high idle or poor cold idle


QUOTE(Such914 @ Jun 20 2018, 06:58 PM) *

Hello, my mechanic is finishing up a rebuild of my cars FI system, and we cannot get it to work. We have some parts we know are broken, but replacements haven’t worked either. Are there any known sources for these?

-Manifold Pressure sensor (known as the 'grenade')
-Air bypass valve

The issue that we are experiencing is misfiring and lack of power in the top end. Apparently they have tried 3 sensors to no avail. It is a ‘74 2.0.

Thank you!
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