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StockNazi
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Joined: June 18, 2004
Posts: 3051
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 Posted: Thu Mar 01, 2012 10:00 am Post subject: 1970 914 fuel injection issues |
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i have a 70 914 and i believe i am having trouble with the fuel injection
the car was not ran since 1992 so i cleaned out the tank bought a new fuel pump, cleaned ignition points, etc.
i am getting fire to all cylinders and compression is good on all 4.
the car starts up just fine, it even idles. it appears one cylinder is not firing and another fires, then it dosent
will the distributor contact points in the distributor cause this problem?
i havent cleaned them yet
any idea on where to start from this point?
any help appreciated
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type241
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Joined: June 02, 2006
Posts: 591
Location: MOSES LAKE, WA
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| Posted: Thu Mar 01, 2012 11:09 am Post subject: |
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There are numerous components in the FI system that need to be checked. One of the most common issues I found was the thermo time switch, temp sensors need to get grounded better or cleaned up.
Send your injectors to WITCHHUNTER PERFORMANCE in Woodinville, WA.
I have had many sets rebuilt for $120 and in less than a week.
There are also those pesky air intake leaks that are EVERYWHERE on these engines. CHECK EVERY HOSE AND RUBBER CONNECTOR!! |
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Hamsterben
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Joined: December 05, 2011
Posts: 140
Location: Damascus Oregon
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| Posted: Thu Mar 01, 2012 9:39 pm Post subject: |
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| Take it apart and clean the whole thing new vacuum and fuel lines the put it back together and see if it runs that's what I did when I had a 914. |
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hammy
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Joined: September 07, 2006
Posts: 27
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| Posted: Sun Mar 04, 2012 12:03 am Post subject: Re: 1970 914 fuel injection issues |
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| StockNazi wrote: | i have a 70 914 and i believe i am having trouble with the fuel injection
the car was not ran since 1992 so i cleaned out the tank bought a new fuel pump, cleaned ignition points, etc.
i am getting fire to all cylinders and compression is good on all 4.
the car starts up just fine, it even idles. it appears one cylinder is not firing and another fires, then it dosent
will the distributor contact points in the distributor cause this problem?
i havent cleaned them yet
any idea on where to start from this point?
any help appreciated |
Start with the dist. Trigger points as you mentioned. Pull them out of the dizzy and check condition. Check ground points on top of engine case in the center, likely hidden by the FI intake plenum. These are your injector grounds, make sure they're clean. Check relay board on drivers side of engine compartment. Pull out and clean relays and all connections. |
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StockNazi
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Joined: June 18, 2004
Posts: 3051
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| Posted: Tue Mar 06, 2012 9:44 am Post subject: |
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i removed the dizzy and cleaned the injector points; they looked ok to me
not the problem, still runs the same , like crap
ill clean and check grounds and see what happens
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type241
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Joined: June 02, 2006
Posts: 591
Location: MOSES LAKE, WA
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| Posted: Tue Mar 06, 2012 10:38 am Post subject: |
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| If your car sat for 20 years, your FI needs 100% rebuild!. Strip it to the longblock in car and replace, tighten, and fix all the components. You will find intake leaks and such that you didn't even know existed. I have NEVER had a FI engine run well from sitting. VERY finicky when right and easy to get wrong. |
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Shadd
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Joined: January 18, 2007
Posts: 863
Location: Athens, Ohio
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| Posted: Sat Mar 10, 2012 9:42 pm Post subject: Re: 1970 914 fuel injection issues |
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| StockNazi wrote: | | ...the car starts up just fine, it even idles. it appears one cylinder is not firing and another fires, then it dosent... |
Does it idle ok and then eventually warm up then run rough and then eventually die if you were to drive it?
If so . This is typical of a faulty temp sensor (otherwise known as the TS2 sensor).
In a properly functioning Bosch D-Jetronic system the temp sensor is basically a "resistance thermometer." When the engine (and sensor) are cold the sensor will show a higher electrical resistance and the engine will run slightly rich. As the engine warms up the resistance goes down which tells the computer to lean the mixture slightly.
This is all great so far.
Now in your crusty old Porsche, which has been sitting for 20+ years you have an unknown amount of resistance in the wiring and in the sensor.
An analogy might be helpful here. Imagine that a properly running engine is like a properly functioning relationship. In this analogy the engines fuel/air mixture is your Wife. As we all know her stability depends on her mother. So, the TS2 temp sensor is like your mother in law. Having a faulty TS2 is like having a Bi-polar mother-in-law. You can tweak and change and fiddle but you are not really going to get anywhere unless you correct the problem.
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StockNazi
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Posts: 3051
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| Posted: Wed Mar 14, 2012 7:50 am Post subject: |
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ok i seemed to have made some progress on this car.
i cleaned the grounds for the injectors on the motor, it seemed to help quite a bit and i believe i have the car firing on all cylinders now.
fuel pressure reg. works well and i have ~30 consistant psi of fuel pressure, at all engine speeds, so i can rule that out as part of the problem.
the car starts up great with just a few turns of starter and idles fine, you dont have to goose the gas to keep it running.
the problem still exists when you open the throttle, it will rev up, but then seems to die and rpms fall; it spudders some then revs back up when you hold the throttle open.
could there be a problem with the throttle switch? i removed mine and clean/inspected it ; dosen't look like its burnt in any spots or obvious problems. best way to test this switch? best way to test temp switch suggested in above post?
thanks to all for bearing with me on this, fuel injection is NOT my forte;
i am trying to keep this car as og as possible as it is a og milage 55k og paint car. i just don't want to pull this stuff off and go to carbs yet
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broomhandle
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Joined: August 04, 2009
Posts: 58
Location: Sacramento
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| Posted: Fri Mar 16, 2012 1:27 pm Post subject: |
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I also have a '70 with D-jet. i just had the injector rebuilt.... the FI has a mind of its own, so i am now dumping it and going with a sinlge brand new carb.
its worth it to me. the 40+ old FI and brain is just to old to trouble shoot and keep going.
my 2 cents.... |
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Bleyseng
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Location: Seattle!
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| Posted: Mon Mar 19, 2012 4:01 am Post subject: |
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Single carbs are the worst on the type 4 engines! Poor MPG, poor running....
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raygreenwood
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Joined: November 24, 2008
Posts: 4946
Location: Des moines Iowa
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| Posted: Sun Mar 25, 2012 6:45 am Post subject: |
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| StockNazi wrote: | ok i seemed to have made some progress on this car.
i cleaned the grounds for the injectors on the motor, it seemed to help quite a bit and i believe i have the car firing on all cylinders now.
fuel pressure reg. works well and i have ~30 consistant psi of fuel pressure, at all engine speeds, so i can rule that out as part of the problem.
the car starts up great with just a few turns of starter and idles fine, you dont have to goose the gas to keep it running.
the problem still exists when you open the throttle, it will rev up, but then seems to die and rpms fall; it spudders some then revs back up when you hold the throttle open.
could there be a problem with the throttle switch? i removed mine and clean/inspected it ; dosen't look like its burnt in any spots or obvious problems. best way to test this switch? best way to test temp switch suggested in above post?
thanks to all for bearing with me on this, fuel injection is NOT my forte;
i am trying to keep this car as og as possible as it is a og milage 55k og paint car. i just don't want to pull this stuff off and go to carbs yet |
I got into this late because I do not browse this forum much. You found part of the issue which I would have mentioned at the beginning had I been here.
A piece of troubleshooting knowledge that can help: in D-jet...if you are having a single cyclinder misfire and ignition has been correctly ruled out....the ground point for that injector is almost always the cause. Why?
Because the injectors fire in pairs. If its the trigger point that fires that pair...both injectors would be off.... not just one.
You ask if it could be the TPS. In this case...not likely. The TPS only operates in two modes:
(1) While it is in motion. It is the forward movement while thethrottle is opening that passes over the contact strips giving extra injection signals.....and again...it would affect the injectors in pairs.
That brings us to another point.....because of the slightly odd injection moment timing of D-jet....that being that the timing for injector openeing of two cylidners is quite close to being correct and the injectors open while the intake valve is somewhat open....but two inject while the valve is closed.....which is noticable at low rpms.....its very difficult to diagnose an injection problem (if thats what it is)....as affecting just one cylinder when your rpm is higher than idle (meaning while you are revving it). Both could be being affected but one is simply worse because its the out of time cylinder.
(2) The TPS also has the function..depending on year...of shutting off all fuel on deceleration. To do this...it has a pair of poles or contacts between which a forked, spring loaded contact floats. There is a tolerance of float to this switch. It is this tolerance that you are biasing forward toward acceleration...when you do the adjustment to the switch (which is explained incorrectly or incompletely in most of the books). If the switch is adjusted incorrectly....it causes a slight but very quick and notciable hesitation off the line...but only for an instant.
And....while maintaining rpm....gas pedal not in motion...at part throttle ..say anywhere from 1000 rpm on up.....if the TPS is adusted improperly.....it can cause the forked contact to float back and forth between shut off and fuel on when it should not...causing a stumble called "the bucking syndrome".
So when you are diagnosing a possible injection misfire problem.....you need to be very diligent in observation of the symptom to be sure if its a TPS issue.
You can add to this...the fact that late model Bosch replacement TPS's....those made in the 80's and 90's.....many had excessive float tolerance between forked switch and contact poles making them virtually impossible to really accurately adjust without some corrective action.
The fact that you corrected much of this by cleaning grounds is indicative of the most common problem with all D-jet....the wiring harness.
The harnesses...though the quality of build was excellent....the quality of connector design was the worst ever designed. Bosch and AMP found that the system was defective in that it could lose proper connectivity with a little as 25 cycles of plugging and unplugging. This is without vibration, heat expansion and possible moisture. This is why they never used that connector system on any injection system ever again.
Idealy...if you like this car...I would replace the harness unless the wiring is perfect (all pliable no crispy spots)...and in that case...I would replace all 23 compoent end connectors and use proper factory crimps iwth something like a palladin crimper (crimpers can be had on amazon for as low as $40-60...connectors are available). You would be amazeed at the difference with a harness that has clean tight connectors and no cracks in the wiring. There are two people on the forms that rebuild harnesses for D-jet and do factory quality work. Do a search.
If wiring gets ruled out.....check your fuel pressure stability....with a good gauge..while running and accelerating. No more than 1 psi of variance is allowed if your system is tightly tuned.
Also..check that your timing, advance and valve adjustment is dead on. If your ignition timing is off....it causes njection timing to be off. If its off far enough...it causes such large vacuum signature changes that it literally affects fuel pressure by causing the MPS to make wild swings in injector pulsewidth. This can be seen with a pressure gauge.
All of that being said....the symptom you are having...i would wager is affecting more than one cylinder. It is also symptomatic of vacuum leaks.
Question: has the back aluminum plug of ther MPS had the epoxy removed and has it been tampered with? It is not just a plug screw...its the ajdustment for the outer full load stop and can cause this symptom.
Also...is there a PCV valve in the oil breather on your engine? If so...that is also a problem that causes this symptom. It was an afterthought on these engines and its untimed fluctuation dumps vacuum into the plenum right next to the MPS vacuum intake...which can cause wild fluctuatiosn of fuel mixture during throttkle transitions. Many of us who work with D-jet on 411 and 412....which is identical to your engine...have gotten much better results by getting rid of the PCV and putting in afixed opening or orifice of about 3-4mm...and then retuning idle mixture at the MpS.
Ray |
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