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Old 05-26-2006, 05:52 AM   #1
theman352001
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D-jetronic experts, help please

Hey guys & gals, sorry for the length, would like to be thorough.

Past Status: '74 Porsche 914 2.0 was running great 2 years ago. Took it to a gas station to fill up a gas can (no gas was put into the car's tank) and as I was leaving the car died. I tried to start it a couple of times and was able to get it to run but as soon as I would try to give it some gas (not in gear) the car would die. The only thing I noticed differently was that the fuel pump didn't sound right.

Back then I tested the fuel pump for flow and pressure (without car running) and both seemed good. The car would start periodically and idle fine but I could not touch the accelerator without it dying. The pump still didn't sound right however.

Current status: Pulled the '74 pump and rigged up a '75 pump that tested good for flow. '74 pump seemed a bit weak on flow. Car will not start at all. I am not even getting any firing.

Plugs are working fine with nice fat sparks. Also, the 2 driver's side injectors are firing a good spray of fuel. (I did not check the passenger side - assuming they are also firing)

I have also checked the fuel filter and it is flowing fine.

Next on my list of things to check:
  • Make sure timing hasn't somehow jumped position
  • double check Crane HI-6 ignition system
  • temperature sensor

I am interested in any other thoughts or past experiences that you may have had. What else should I be checking? Have you had a similar problem and what was the solution?

Thanks in advance.
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Old 05-26-2006, 08:23 AM   #2
Wally
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Don't profess to be an expert, but check:

constant fuel pressure;
ignition timing;
blocked air filter;
glagged fuel filter;
faulty thermostat is keeping the engine cold;
temperature sensors;
spark plugs;
leaking injectors;
knackered pressure sensor or leaking hose;

my guess (and that is all it is) would be the throttle position switch needs attention for proper fuel enrichment.
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Old 05-26-2006, 10:58 AM   #3
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I'll move this, it'll probably receive more input in the R&M section!
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Old 05-26-2006, 05:54 PM   #4
theman352001
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Thanks for the list Wally. Here is a little input on some of the items:

Quote:
Originally Posted by Wally
Don't profess to be an expert, but check:

constant fuel pressure; Had checked w/ old pump - will dbl check with new
ignition timing; Will do this weekend
blocked air filter; Air filter is off right now so not the issue
glagged fuel filter;
faulty thermostat is keeping the engine cold; air cooled so no thermo
temperature sensors; will do this weekend
spark plugs; working good
leaking injectors; Driver's side are fine
knackered pressure sensor or leaking hose; hoses good, will dbl check sensor

my guess (and that is all it is) would be the throttle position switch needs attention for proper fuel enrichment.

The TPS is rarely fails in this manner on these cars but I will double check.

Thanks again for your input.
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Old 05-27-2006, 12:11 AM   #5
Wally
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I'm a bit of a silly Billy listing the t/stat. That's brain in neutral for ya.
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Old 05-27-2006, 12:42 AM   #6
theman352001
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Quote:
Originally Posted by Wally
I'm a bit of a silly Billy listing the t/stat. That's brain in neutral for ya.
I thought maybe you just had a few too many cold ones. In fact, that sound's like a good idea.

Down the hatch mate.

I'll let you know what I find out after this weekend.

.
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Old 05-27-2006, 02:59 AM   #7
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Quote:
Originally Posted by theman352001
I thought maybe you just had a few too many cold ones. In fact, that sound's like a good idea.

Down the hatch mate.

I'll let you know what I find out after this weekend.

.

Well the truth is I had been to a tappenaki earlier on and downed a few.
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Old 05-30-2006, 03:20 PM   #8
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Ok Wally, here is what I found out......

1: I tried to start the car right off the bat and it did fire and try to run. I had it running on it's own but as soon as I applied the gas she died. I did not get it started again after that.

2: Dbl checked timing and it was on.

3: Checked fuel pressure w/ the new pump and it was about 33 PSI so I adjusted it back down to between 28 and 29 PSI. It was constant although I was not able to perform a running test.

4: Checked the Manifold Pressure Sensor and it checked out good.

5: Checked the Intake Air Temperature Sensor and it was in spec.

OK, here are the areas I checked that didn't "check" out.......

6: Checked the Thermo switch that operates the cold start injection valve and got an open circuit from the lead to any ground point. This switch usually operates only at cold temps so it should not be the problem.

7: Checked the Cylinder Head Temperature Sensor and received a value of 5.1 ohms from the lead to any ground point. This value is about double what I have seen it should be. This could be the smoking gun.

8: Noticed that I had standing fuel in the intake manifold. Checked the cold start valve and it was not firing or leaking so I am not sure where the fuel came from. I decided to disconnect it anyway since I don't run the car in the cold. (I disconnected both fuel and electrical)

My thoughts at this time......

I think I am experiencing a rich running condition and the car is flooding out. This is supported by the Cylinder Head Temerature Sensor value and the fuel in the intake. The main question I have is why I am getting fuel in the intake. Perhaps the cold start injector is firing periodically. To test the other idea, I am going to have to find a new Temp Sensor.

Given what I found, do you have any other thoghts?
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Old 05-30-2006, 11:28 PM   #9
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The D- Jetronic is not greatly different from the fuel injection systems on Jap cars from the late 80's, but it does have some quirks.

Maybe if I ramble something will click:

the fueling is governed by : air temp sensor, coolant sensor, MAP sensor and TPS switch. The synch pulse for the injectors is from a reluctor pickup in the dizzy.

The air temp sensor enrichens when the incoming air is cold, the engine temp sensor enriches when the engine is cold and leans when the engine is hot and the air is cold. I think the temp sensor resistance hangs around the 100's of ohms, while the engine one is in the 1000's.

Your time controlled cold start injector works in conjunction with an air valve. On the porsche the air valve is probably electrically controlled and allows some bypass air around the throttle plate which raises the MAP sensor reading and thus the fueling.

As I recall the TPS switch is stepped, so that the sweep arm gets pulses rather than a continuous voltage divider. Each of the steps is used to fuel enrich by giving the injectors an extra shot over and above what the ECU is giving. You can check the TPS by turning the ignition to the on position (dash lights on) and manually rotating the sweep arm quad while listening for the injectors clicking each of the twenty odd steps through the range.


Injector seals need to be in good nick as do the manifold and TB gaskets.
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Old 05-31-2006, 01:52 AM   #10
theman352001
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Wally,

For the most part, you are correct. The only exceptions are the coolant sensor (you still want to add coolant to my car) and the TPS. In the '74 914, the TPS it is a continuous voltage divider. The main issue with them is wear on certain areas that correspond with driving at a certain constant speed.

The test you mention for the TPS will not work on my vehicle. I did build a tester for my TPS that allows me to check for flat spots however. I did not find any last year when I tested it.

I think I need to look closer at the Cylinder Head Temperature sensor. I am looking for a variable resistor that I can put in it's place to see if I can get the car running. If that works, then I will look at swapping out the sensor.

I also need to look into my injector seals. I know that one of them on the driver's side should be replaced. I do not think this is the main part of my problem however. I have been running the car for a number of years with them in their current condition. Then again, sometimes these things can compound on each other and make a small problem into a large one.

Thanks again for all your input. On a side note, I enjoyed a few cold Foster's today after a round of golf. They definately hit the spot.

.
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Old 06-15-2006, 04:10 AM   #11
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Thought I would update this since I have done a little more work on it.

I put a variable resistor in place of the CHT and that did not seem to have any effect on the starting issue. Yes, I tried different values within the listed range but no luck.

I also changed out the filter, drained the gas tank, and put some fresh gas in. Still no luck.

It is however firing a bit more than it had in the past. I also got a noid light set and checked the injectors. They seem to be firing on regular intervals.

Next on my list is to check the compression and perhaps pull the valve covers to see if there is anything out of wack there.

On the plus side, I am going to a 914 function this weekend so hopefully there will be somebody I can talk to that may have additional informtion.

Still looking for other thoughts regarding this issue. Thanks for giving it some thought.
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