fuel pump surging, why?? Options

[Tab914]

Another one for you guys...........

Here is the problem I am trying to fix. Whenever the needle in the temp guage gets to about 1/4 the fuel pump starts surging. This causes the idle to start to go up and down in rythm with the fuel pump. Also when under load the car stutters and shudders and kinda wants to choke.

Before the car gets up to that temp. it runs nice and smooth, strong on acceleration and no poping or backfiring on decel or anything. Just sounds great and runs fine. Idle is where it should be and fuel pump does not surge.

Here is what has been done. -Valve adjustement
-Dwell adjustement
-Timing adjustement
-Tested MPC as per proper ohms.
Parts I have changed- coil, plugs, ignition points, trigger points, condenser, rotor, cap and wires.

Questions:- what could make the pump surge like that?
-does it make a difference how the MPC wire goes into it's conector?
-How do I properly check the head temp sensor.
-Could the intake temp. sensor be the cause.

I am at a lost. Feel like I am going in circles. (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

Has anyone had this kind of problem??
Desperate for advice. (IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif)

Thanks, Dominic.

forgot to add. car is a 1974 2.0 with stock fuel injection.

[mihai914]

If by surging, you mean the pump makes a different louder noise. Usually when the pump changes tone and get louder it's from lack of fuel.

Your fuel gauge may not be correct.

When was the last time the fuel filter was changed?

You may also have a dirty gas tank, did you ever have a peak inside?

[Dave_Darling]

Do you mean the MPS? Manifold Pressure Sensor? If so, you have D-jetronic FI, which is an important distinction.

How do you know the fuel pump is surging? That would be an unusual failure mode. Does the fuel pressure go up and down? (Do you have a gauge?)

I would guess that you have a vacuum leak somewhere. Another possibility is that your mixture is going somewhat lean when the engine is at warm idle. A few clicks clockwise on the knob on the ECU may help with that, at least somewhat.

You test the Head Temp Sensor by unplugging it from the harness (the plastic box connector stays on the harness), putting one probe of your ohmmeter on the metal connector on the HTS wire, and the other probe on the cylinder head. Should be 2K-3K when cold, <100 ohms when the engine is at operating temp.

The MPS connector can go in either way; it doesn't matter which way around it is. The two outer pins connect to one coil in the sensor, and the two inner pins connect to the other coil. They don't care which way around they are.

Finally, for all of your D-jetronic informational needs, see:
http://members.rennlist.com/pbanders .

[Tab914]

Thanks guys! Ya I meant MPS. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

Mihai! What I mean by the fuel pump surging is that I can hear it change sound. It kinda whirrrrllllss and then nothing and then whrillllss again and so on.

Dave! I will try cranking down on the knob on the ecu and see what happens then. As for a vacuum leak, I have all new hose installed but I guess that is still possible.

I don't have a pressure guage. I remember putting on a new fuel filter but only one that looked liked the previous one and never by actual product #. That bad?? Also in the engine bay are plastic fuel lines (which I know I should change and will) and in the lines I can actually see air gaps when the fuel is just sitting there (engine off) and it never seems to be full solid of fuel when running. (air bubbles) This is probably a stupid question but....... is that bad??
How do I fix. I'm guessing I would need to drain all the fuel but then how do I get the air out of the lines.

Thanks again.

[bd1308]

dude, dont play around. mine did EXACTLY the same thing (READ EXACT) and I ended up toasting the engine. Ran way WAY too lean. got fed up and changed engines.

fuel pump had higher pitch and everything...then all was well and then pitch changed up and then all-good.

sigh.

i changed fuel pump, fuel filter, MPS(to known good one), checked wiring, etc....

your pump is in the stock 70-74 place isnt it? ask me how i know.

[Dave_Darling]

The air will get purged without any extra effort on your part. The bubbles will (eventually) wind up in the return line, and go back into the fuel tank.

Not sure what's going on with the pump being intermittent. I would suspect the pump, the wiring to the pump, the pump relay on the relay board (especially that!!), the relay board itself, the connections to the relay board, the fuses on the relay board.... Hmm, not sure what else offhand. The trigger points, because they tell the EFI that the engine is still running.

--DD

[mihai914]

To me it sounds like a fuel delivery problem. The fuel pump usually gets noisy when it's either pumping nothing like air or when it's pumping and there is a blockage in the fuel system.

Doesn't really matter what type of filter you put, as long as it's designed for FI and that you follow the flow direction of the filter usually indicated by an arrow or "in" and "out markings.

Also check for any kinks in the fuel hoses.

To check you pressure you don't have to buy and expensive automotive fuel gauge, you can go to your hardware store and buy a water pump pressure gauge along with a nice ribbed cone fitting that will allow you to slip a fuel hose over it.

I would also clean the contacts on the relay board, change the fuse and swap relays.

Usually if you have air in the fuel lines, the air is eventually pushed by the fuel flow.

Was it really hot when this happened, it may be vapor lock if your pump is still in it's original location in the engine bay.

[Tab914]

Thanks guys.

The fuel pump is in front with the master cylinder. I will try all those things Mihai.

I am posting a pic of something mounted on the front of the engine on the passenger side. I can't find this in the books and have no idea what it is or what it does. If anyone knows I would like to know as well. (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

Dave, the hts is coming in a 170 ohms when hot. Does that pass or is that bad.

Here are a couple pics of that thingamajig. The hose conected to it runs down into the engine tin right beside the distributor. The wire coming out the front connects to a green and red wire that goes through a harness and ends up on the corner of the relay board on the rectangle conector. (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

Let me know if you have any ikeas.

Dominic.

[Tab914]

another pic ot that thingamajig

[bd1308]

never seen that before. seems like some kind of AAR device.

[mihai914]

That would be an oil pressure sender, the purpose is to give you and actual reading and not a green light when it's too late.

[bd1308]

woah....i thought it would be cooler looking. like chrome

[Tab914]

Ah! Yes that makes sense. I have the extra gave in the car. So focussed on trying to figure this problem out that I can't think straight. VERY frustrated. (IMG:http://www.914world.com/bbs2/html/emoticons/mad.gif)

[Dr Evil]

QUOTE (Tab914 @ Aug 1 2005, 05:52 PM)

When temp guage gets to about 1/4: -fuel pump starts surging -idle starts to go up and down in rythm with the fuel pump -when under load the car stutters and shudders and kinda wants to choke -All good before operating temp. Here is what has been done: -Valve adjustement -Dwell adjustement -Timing adjustement -Tested MPC ohms Parts I have changed - coil, plugs - ignition points - trigger points - condenser - rotor - cap and wires Car is a 1974 2.0 with stock fuel injection.

Well, you have obviously attended to the ignition aspect of this. The valve adjust is a good idea as well. Now, you will best be served by a fuel pressure gauge hooked up tellign you/us exactly what pressure you are dealing with. It should be 29 or 39 IIRC (Check to make sure as it needs to be exact.)
Things that will affect your fuel pressure after warm up:
1-blockage in the line
2-faulty pressure regulator
3-your brain having siezures causeing the injectors to fire erretically
4-Head temp sensor


IMHO, changing the engine will change nothing fuel, or electrically related.
The fact that your engine seems to be having fits after warmed up leads me to think that it may be your brain as fault 1 will likely be non intermittant, 2 might be and is an easy replace as we all have a few of these parts lying around, 3 would suck but seems to me to be likely, 4 would be a constant rich condition (again, not intermittant). If it is doing the exact same thing each time then many of these faults are far less likely than a brain issue.

The major symptom is SURGING when hot. We do need more info on your fuel pressure situation to make further prognostications.

Things to look out for:
-What is taken out or put into the FI circuit uppon warm up?


Can you get a brain from someone else to test?

[Dr Evil]

Also, check to see if the TPS is in the circuit before warm up. If it is not it is anotehr place for fault after warm up. I think that I might have heard that the brain does not listen to input from the TPS untilt he CHT sensor reaches close to zero. Check PBAnders page for clarification.

HTH

[Tab914]

Thanks Dr. Evil.

I will perform a fuel pressure test hopefully tomorow. I need to get pressure guage first. As soon as I have results I will post them. The PO had put in a new fuel pump and I am trying to find it in my papperwork to see if it was the proper one as I don't have the car jacked up at the moment. The TPS is brand new from 2 weeks from PP and it was installed as per the tech article on PP.
I was suspecting the HTS but the ohms seem right on it. Fuel delivery has become my main focuss and hopefully a pressure test will tell us more. If the fuel pump is not the exact right one, would the engine run anyway??

Thing is this only starts happening when warmed up. I don't have a spare ECU for 2.0 lt but do have one for 1.7lt. Any possibility of it working enough just to check??

Could I be getting vapor lock from the fuel lines in the engine bay?? Tried to take it for somewhat of a spin just to see how it would react today after warm up and it just coughed real bad under load as usual. Feels like the fuel is not getting there.

What do you think? (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif)

thanks again Dr Evil.

[Tab914]

Well from the paper work the fuel pump is the right one. The PO had gotten it from a PORSCHE dealership. # 311-906-091 $550.00 Canadian. Good news is I had bought the car for $800.00. Anyway when I picked up the car the PO could not get it running. After fiddling with the fuel pump (disconecting and reconecting a dozen times) I got it to run. Is it possible the hoses are in the wrong ports but the car still runs? (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif) Seems unlikely to me but you probably know better.
As for the vapor lock from the fuel lines in the engine bay as I asked about earlier, am I having symptoms that resemble vapor lock?? (not sure what vapor lock does).

[mihai914]

Dominic, did the PO tell you why he replaced the fuel pump? And before you purchased the car has it been sitting for a long while with old fuel in the tank? We'll need the pressure reading to go any further.

[Tab914]

Hey Mihai!

I don't think that the last owner was the one to relocate the fuel pump. He didn't seem to have much of a clue. So I don't know.

I am trying to get a fuel pressure tester and hopefully get that done today.

Another thing that just dawned on me and I guess it should have sooner is that the Heat temp. sensor is located neer the #1 cylinder (in a makeshift hole in the engine tin) where it says everywhere (the books) that it should be near the #3 cylinder. Would that make a difference in any of the readings??
Is there a port in the head on that side of the engine for a temp. sensor or was some weird stuff done here??

I am baffled. (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

Is it possible that the engine was rebuilt and that the heads were switched around by mistake. Would they fit and still work????

[Tab914]

Well...., didn't have time to get a fuel guage today so that will have to be tomorow.
Still curious though if anyone knows about what I was asking about the heads being switched around. Is it possible?? HTS is now besides cylinder #2 (not 1 as previously stated) as opposed to being beside cylinder #3. Now if you were to switch them around that is where it would end up. Seems to me like that is what happened.

what do you think?

more to come tomorow with the fuel pressure. Thanks to all who are helping on this one.

Cheers, Dominic. (IMG:http://www.914world.com/bbs2/html/emoticons/beerchug.gif)