Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 914 & 914-6 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: Mar 2018
Posts: 5
Weird fuel delivery/running issue

UPDATE: Issue solved. See post below for more info.

Hello. I'm new here but not new to the VW/Porsche/Audi world. First of all, many thanks to the contributors who've posted all of the helpful info. I've been poring over threads for a couple of days and they've helped me get to where I'm at. OK:

The short version:
76 2.0 runs rich AND runs without the fuel pump running. Connecting pump power causes it to stall.

Long version:
Car was brought to be by a friend who'd had some work done. It ran rich, rough, backfired and had no power. The car apparently hadn't run for a while and had (among other things) a rusty fuel tank. He had his "guy" replace the fuel tank, hoses and pump. He also cleaned the injectors. The pump is located on the passenger side of the engine bay (not optimal, I know). It's also not the correct pump. Part numbers:
FP7901-016
580464070

My understanding is that this pump is too high pressure and delivers too much fuel, which will eventually take its toll on the regulator. But I digress...

Looking the car over, I adjusted/corrected/repaired the following:
1. Checked the return line to make sure it isn't clogged.
2. Set fuel pressure to 2.0 bar/29.4 psi
3. Gapped plugs
4. Gapped points and set dwell
5. Set timing (had to use the paper template to make 27 BTDC mark)
6. Checked both temp senders with meter
7. Removed and cleaned grounds at back of motor
8. Found coil was wired backwards (weak spark). Switched wires and cleaned terminals
9. Removed distributor injection trigger points, dressed points and bent tabs to compensate for massive wear (points only opened for about 5). Set points to open for ~160
10. Checked cold start injector for leakage
11. Checked injectors for spray pattern - lots of fuel/good atomization
11.5: Swapped pressure sensor for one that help vacuum better (coil resistance OK)
12. Pulled computer harness. Checked power, ground and several other connections with VOM
13. Removed/cleaned throttle switch (circuit board) and calibrated per tech bulletin here
14. New cap, rotor and wires (installed by previous guy)
15. Verified firing order.
16. Hokey/incorrect fuel pump wiring by previous guy. He installed a relay and is powering the pump off of the battery, using the coil positive as a trigger wire for the relay coil. So the pump runs whenever the key is on and is not mitigated by an ignition/starter signal. Bad.

The above list is not in order. I just wrote it from memory.

Thanks to the coil rewire and the trigger point repair, the car went from running on two (diagonal) cylinders and backfiring/sputtering to running smoothly on all four, albeit rich and not really wanting to idle. So I'm really close, but here's where it gets weird:

I was running it, working the throttle by hand, adjusting idle air and checking to see it the aux air valve was going to close when it warmed up a bit when I noticed that I'd forgetter to reconnect the fuel pump relay. Why was the car still running?? And running very rich, for that matter (blackish smoke, burning my nostrils). I reconnected the pump and the vehicle dies immediately. (connected directly to battery positive for this rather than coil ignition plus)

My friend assured me that there is NOT a second pump under the car, as he's had the tank and stuff out of it. It's like it's running by siphoning gas! WTF?

I just pulled the pump line...no flow out of the pump when it's running, zero pressure at the gauge (gauge is connected inline between the two sets of injectors. I ran it for a bit. I'm sure it would have died eventually but I'm shocked that the injectors can even spray with no pressure. So here's the conclusion I've come to:

When they other guy pulled/cleaned the injectors, he somehow ruined them and while they don't leak, they deliver too much fuel, even with no pressure in the lines. The excessive delivery would obviously cause a rich running condition and the pressure when the pump is running worsens it significantly.

Update: checked injectors and all are 0280150019, which is listed as 73-74 2.0

Any thoughts? Thanks!

Last edited by sciroccojim; 03-04-2018 at 05:30 PM..
Old 03-03-2018, 03:07 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Administrator
 
Dave at Pelican Parts's Avatar
 
Join Date: Dec 1969
Location: Silly-Con Valley
Posts: 13,966
Garage
Send a message via AIM to Dave at Pelican Parts Send a message via Yahoo to Dave at Pelican Parts
My guess is that the CHT is unplugged. That tells the FI to make the mixture very rich by opening the injectors for a long time. With low fuel pressure, that happens to get enough fuel into the engine so that it runs--but the fuel dribbles rather than spraying so the mixture quality is terrible. (The mixture may not be that rich; it might be that the fuel isn't burning well because it is poorly atomized.)

There may be vacuum leaks that let enough air in that the engine doesn't stall.

I remember a problem back in the Porschephiles or Rennlist days where a D-jet 914 would only idle, and only when the fuel pump was not running. It was a couple of problems, one of which was an unplugged CHT sensor.

--DD
__________________
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling
Old 03-03-2018, 06:41 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
Join Date: Mar 2018
Posts: 5
Thanks. I have checked both sensors but I'll recheck in the morning. Actually, I ended up redoing the CHT connection to the harness because it was buggered. I used to built harnesses for a living, so I use the good stuff for repairs. But I'll check the value at the ECU in the morning to be sure.

In the meantime:

Big development. I found that two opposing cylinders are spraying a steady stream of fuel whenever the key is turned to the "on" position (not cranking). This likely corresponds to input from the injection trigger points in the distributor and I'd guess that rotating the engine would cause the other two injectors to start spraying. I see that ECU pin 18 gets 12V+ when the ignition key is in the "start" position, so I'll check that, but are two injectors supposed to spray continuously when the starter position is engaged (with the engine not turning)?


I just located/downloaded a scan of an original Bosch VW/Porsche D-Jet shop manual, so I'm reading that now.
Thanks again.
Old 03-03-2018, 06:46 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Jun 2002
Posts: 475
First thing I would do if you don’t want to replace the injectors yet you suspect they are bad is take them to an injector cleaning shop. Those places have instruments to check and measure exact fuel output. If they comeback ok then you need to take a hard look at the fuel pump. It’s crazy when someone Frankenstein’s a car and you have to unFrankenstein it. Now this might take a little research on your part but years ago I bought an electric fuel pump from autozone that was not expensive and had the same specs as the fuel pump for a 914.
I’m not sure if this is the case but at the return line to the tank is a valve similar to cis, one way valve. Also there is a website www.bowlsby.net that could help. Sorry, not much more help than this.
Old 03-03-2018, 06:49 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
Join Date: Mar 2018
Posts: 5

Big development. I found that two opposing cylinders are spraying a steady stream of fuel whenever the key is turned to the "on" position (not cranking). This likely corresponds to input from the injection trigger points in the distributor and I'd guess that rotating the engine would cause the other two injectors to start spraying. I see that ECU pin 18 gets 12V+ when the ignition key is in the "start" position, so I'll check that, but are two injectors supposed to spray continuously when the starter position is engaged (with the engine not turning)?


My understanding is that the starter signal from terminal 50 is only used to operate the cold start injector. There's no coil/tach input, so how does the system know when/how much to inject? I guess the injectors don't pulse until the trigger points start to oscillate? In my case, it's full blast on two cylinders with the key on.

Last edited by sciroccojim; 03-03-2018 at 07:23 PM..
Old 03-03-2018, 07:19 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: Mar 2018
Posts: 5
Quote:
Originally Posted by Dave at Pelican Parts View Post
My guess is that the CHT is unplugged. That tells the FI to make the mixture very rich by opening the injectors for a long time. With low fuel pressure, that happens to get enough fuel into the engine so that it runs--but the fuel dribbles rather than spraying so the mixture quality is terrible. (The mixture may not be that rich; it might be that the fuel isn't burning well because it is poorly atomized.)
I did already check both sensors (and repaired bad CHT wiring) but I'll check again at the ECU. But the system is dumping fuel into the cylinders, so something bigger (like a bad ECU) is happening.
Old 03-03-2018, 07:25 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Administrator
 
Dave at Pelican Parts's Avatar
 
Join Date: Dec 1969
Location: Silly-Con Valley
Posts: 13,966
Garage
Send a message via AIM to Dave at Pelican Parts Send a message via Yahoo to Dave at Pelican Parts
It sounds like an output transistor has failed in your ECU. That can cause the injectors to turn on and never turn off.

Have a spare ECU to test with?

D-jetronic info: http://members.rennlist.com/pbanders . That contains just about al of the D-jet knowledge that currently exists. Including schematics of the ECU circuits!

--DD
__________________
Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling
Old 03-04-2018, 08:33 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
Join Date: Jun 2002
Posts: 475
Sciorrojim

What state are you in?
Old 03-04-2018, 04:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
Join Date: Mar 2018
Posts: 5
For some reason my permissions here are limited. I can't quote anyone else's post, so I'll do it the old-fashioned way.

@jess p: I'm in NJ

@Dave: Bingo. I happened to read Paul Anders's very excellent info last night and came to the conclusion. I'd actually said to my girlfriend: "There's no reason these injectors should be stuck on. Has to be a messed up semiconductor in the ECU." I think there was some recent welding done to the car and that might have done the damage. I'm tempted to replace the offending transistors and sell the ECU to recoup some costs!

So I swapped out the ECU and it runs like a dream. I'm a little embarrassed for not noticing the "stuck" injectors, but I wasn't the first person to work on this....they just told me it was "running really rich". After I figured this out, they said "Oh, yeah, there was a ton of fuel in the cylinders and it hydro-locked. We had to pull the plugs and push it around the lot in gear to get the gas out." - Uh, that's more than "running rich." The other mistake I made was not swapping out the ECU. I'm kinda stubborn, eschewing "parts swapping" in favor of careful diagnosis. I carefully testing all of the components and made several corrections/repairs, but I had the second ECU and could have easily swapped it in just to see what might happen. On the other hand, I didn't realize (until I read Anders's article) that they're pretty cross-compatible. I didn't know where the donor ECU came from and there were no visible part numbers, so I feared catastrophic results. But it has the idle mixture potentiometer on top so it must be from a later car...

Thanks for the help, folks. I hope this helps someone else at some point. I can now say that I'm pretty versed in D-Jet diagnosis and repair!

Jim
Old 03-04-2018, 05:43 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 01:29 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.