injector wires shorted, what could it damage?

924sownerga · 08-19-2007, 01:17 PM

In looking for a vacuum leak; I hit my front injector wire and the car died. I pulled back the rubber boot and discovered a short. (2nd photo) If I seperate the wires the car still runs with the same surging from 1500 rpm to 2000 rpm and won't idle. Could this be causing my issues. Is it possible to fry the computer with such a short? Also, I found another plug that looks like an injector plug under the intake manafold. The plug is slightly disfigured from heat. I included a photo of that as well. Any idea if this is supposed to connect to anything? I shot it in the area of the air intake and temperature sensor as those plugs are close.

Special thanks to those that have helped up to this point. I appreciate the guidance.

Techno Duck · Techno Duck's Garage

Im fairly certain that black connector is supposed to be disconnected. There is a blue one that looks similar that is for the DME temp sensor on the top of the block.

I dont think the shorted wires would cause you to fry the DME. If the main ground on the bell housing is not connected and you try to start the car, then you will fry the DME.

Icey1174 · 08-19-2007, 02:07 PM

Fix the shorts and try it. If the DME was fried then I would guess it would really be fried and not work at all. I would be willing to bet your surging to be coming from that short. That would be the first thing I would fix.

That black fuel line that is in the second pic is also a big problem for these cars. It was a safety recall. When you have the rail off make sure you inspect that hose real well for dry rot and bubbles. The heat from the cam housing causes it to break down quickly. I caught mine just in time before a fire or explosion under my hood.

924sownerga · 08-20-2007, 02:50 PM

I inspected the system for vacuum leaks, and fixed the short. No luck on the surging problem. Does anyone know what the idle control does or better yet how it works?

DarylJ · 08-21-2007, 03:13 AM

If it's like a 944 motor, you can disable the idle control valve for testing. Take a look at this:
http://www.clarks-garage.com/shop-manual/fuel-08.htm

and see if you have that same diagnostic plug. Double check that its the same for a 924 before doing anything, but that might at least get you in the right direction of figuring out whether its the ISV or not.

924sownerga · 08-22-2007, 04:47 PM

I tried to test the Idle Control valve as per the Clark guide. With no success. I also checked the air system. Any other suggestions would be much appreciated.
Brad

924sownerga · 08-22-2007, 04:52 PM

Can anyone give me pictures of the vacuum lines as they are routed in their car? If you look at my first picture you will see where I have a vacuum line plugged. This does not look good. The car ran with this plugged before, but I would like to get it right. Also, the car ran without an oxygen sensor. Does anyone know what is required to bypass this system. Could having no oxygen sensor cause the car to surge?

Icey1174 · 08-22-2007, 05:01 PM

Try a PM to "Blown944." He knows these engines pretty well. He just bought a Turbo so he has been over on the Turbo board a lot lately. He was a great source of knowledge here.

Techno Duck · Techno Duck's Garage

The car must run with an oxygen sensor. You might be able to jump the plugs on the altitude sensor as i know FRWilk's chip requires you to do this to use his modified fuel maps (which ignore the O2 sensor signal). I am not sure how this would be done though.

I will take a picture of the vacuum line routing on my car later tonight and post it. Probably around 1 or 2am EST.

I am fairly certain the one you have plugged T's off, one end goes to the emissions control equipment behind the drivers side strut tower and the other end goes to a thermovalve that is located on the cylinder head.

EDIT - actually check the pictures on this thread.. they should be helpful.

http://forums.rennlist.com/rennforums/showthread.php?t=348704

blown 944 · 08-23-2007, 06:42 AM

Brad

a couple of things first

was it running fine before the pump swap?
was it running before with the deleted 02?
Is it chipped or a Euro car? Otherwise it should have an 02

The DME is not fried
The ISV is not absolutely necessary from what I have found
I would test your pressure at the end of the rail first to eliminate the new pump as the culprit. It should be around 30 psi at idle.

If it is surging it is probably a little lean.

If the pressure tests out ok I would

1) look for vacuum leaks using a can of starting fluid even under the intake

2)check TPS postion and funtionality (TPS causes the DME to use a idle map when closed)

3) test AFM

once everything is good I would look into some new injector looms

924sownerga · 06:29 PM

Answers to questions: (and update to problem)
The car was running well prior to pump swap
It was running with the deleted O2
It is chipped, I don’t know what kind
I tested the fuel pressure today, it is around 32 psi very consistent even under acceleration.
I need to perform a vacuum leak test of some kind. I really would like to see how the vacuum lines should be run; I can’t find the routing in any of my literature for the 924. (thank you for the link of pictures in previous post) I have assumed it is the same as the 944 But I have something capped that does not look normal. But, the car was running with the vacuum lines as is prior to fuel pump dying.
I need to check the TPS position, I disconnected it to see if this would stop the surging, it did not.
I replaced the injector caps and seals today. (no change)
Thank you for replying, I have learned much from reading your posts to date.
Brad

soxnail · 08-25-2007, 07:15 PM

pm received. I need to do some reading. The DME for the 951 is Bosch # 0 261 200 075 or Porsche # 951 618 121 0X. X is 6 to 8 I think. I need to know what is the part # of the DME used in your car. I see that you have fixed the short in the injector connector. The DME I am familiar with uses a common sink source for all the injectors. If your car is running in any form then the injector drivers are probably ok. You can run without an O2 sensor. The car just runs in a default mode. You said it was chipped then it is modified right ?? What type of chip ? (If the new chip needs the O2 sensor...but I would not suspect that it does). Does the car use the same ISV (idle stabilization valve) as the 944 ?
Finally by surging do you mean the rpm surges up and then kind of dies like a fuel cut off and when it falls it catches and revs up again and so on ?
I will have more questions as I learn about your car.
Sox

blown 944 · 10:36 PM

Can you describe a little more precisely what the hunting symptoms are? Like is it just hunting on idle and then rising to about 1500 then almost dies then stabilizes for a second then rises, falls and stabilizes?

Will it RPM if you try to run it up?

Considering what you have done for testing so far I would rule out the pump swap as culprit and move on.

IMO it souds like it is having a slightly lean condition at idle. It either has a vacuum leak or the TPS is misadjusted allowing it o run off of the AFM signal at idle. Try to cover teh opening a littel to teh intake and see if it stabilizes more.

I again would first look at the sysem for leaks (even small ones)

Also temporarily disconect the vacuum line to the FP regulator (it is the rear one)

I would also look at your engine ground.

I would also try to make sure the TPS is adjusted properly (unhooking it doesn't do what is needed b/c it is actually grounding at idle and using the idle map)

If you cant find a leak and the TPS doesn't do it I may even try to switch the FQS switch to a richer position to temporarily fix it..

If that fixes it Then I would try to unhook the battery and let the DME relearn (it may have a lean adaptation to what was being fed before the new pump)

924sownerga · 08-26-2007, 05:38 AM

Thanks again guys, I am going to do some more testing today. My DME is part # 0 261 200 086 or 944.618.121.05. I took apart the computer but did not know how to remove the chip. It does not just pull out. It appears to be soldered in and there is no brand that I can see on the chip. I took pictures so someone could help identify the chip and also to show the soldering done. I do not detect any loose solders and I will clean up some flux but it looks very clean.

Answers to other questions:
The car only starts if while you crank it you give it gas. Once started the surging is a fairly smooth acceleration and deceleration. It is not like a surge of gas then no gas. I wish I knew how to send a sound file as this would be the best way to describe it. The car will rev to red line and will do the same 500rpm surge at 3000 rpm as it does at 1000 rpm. The engine ground is new and tight. Replaced all battery cables prior to the fuel pump dying. I will let you know how the test of the AFM and TPS and vacuum leaks (again) go today. I am also going to go fill it up with new gas.

soxnail · 08-26-2007, 06:28 AM

So while the car surges +/- 500 rpm it will do it at idle and also when you rev up? If so lets test your Idle control system. If it is causing the problem we can by pass it by disconnecting the idle valve hose from the hard pipe to the throttle body. Now cap both openings (the one to the ISV and the one on the inlet to the throttle.) Start the car you may have to hold the throttle open for it to run. If the problem goes away (you may have bad or rough idle but no smooth surge) then the ISV may be stuck open or is sticking so it does not close till the car is way over on one side or other of the right rpm. The only problem with this theory is that the idle switch in the throttle should eliminate the ISV when throttle is cracked, but the tps may not be set right or the isv may be bad. Try this test and let me know. Don't know about the chip on your dme let me search further.
Sox

soxnail · 08-26-2007, 06:49 AM

Can confirm that the vacuum hose layout of the 924 is same as a na 944 ?
Sox

924sownerga · 08:12 AM

I tested the tps and the vacuum system. It is all ok. The vacuum system is connected correctly except that the one port on the throttle body is plugged. The AFM shows the correct voltage on the car but I have not taken it off for testing.

I am going to change the statement on how the car acts. I now thank that the car acts like it is getting gas then it is starved for gas, then gets another jolt. The reason is that while driving, (road trip from hell) if I chose to decelerate the car seemed to run smooth until I re-accelerated. Also, at 5000 rpms the car seemed to run smoothly for short periods.

I pushed open the flap in the AFM to see if it had resistance, my theory being that if the flap was loose it could swing back and forth causing erratic running. It seems to give consistent pressure to open and fairly good tension.

If I remove the fuel rail with the injectors and crank the engine can I tell if the injectors are firing and if so how fast should they fire. (once / second, 10 times/second....) just an estimate. Should the flow be forceful and enough to wet down a towel or a fine mist or somewhere in between.

One more thought, If you floor the accelerator the car will accelerate in 1 second surges, Imagine the bucking bronco, that is what is looks like as you drive down the road in first or second gear.

I'm about ready to say give me back my Holey Carburetor.

soxnail · 08-26-2007, 08:20 AM

Don't give up yet. To trouble shoot ...
1) does the car surge if you hold the throttle constant or only when the throttle is changing.
2) I would hold off pulling the fuel rail.
3) Can you do the procedure I out lined in my last post ? (ISV etc.)
You are going to have to have patience and help in the trouble shooting frustrating as it may be.
Sox

blown 944 · 08-26-2007, 08:20 PM

So to clarify,

the surging is throughout all rpm ranges?

924sownerga · 08-27-2007, 02:04 PM

ISV test did not do anything. Except, it made it more difficult to start. But it still surged.

The car surges at idle and during acceleration.

I was reluctant to do this test for fear of destroying the engine but it gave me some interesting information.

The car does not surge in all rpms.
1000 rpms it surges to 1500 as described earlier,
2000 rpms it surges to about 2400 rpms,
3000 rpms it surges to about 3200 rpms,
4000 rpms a slight surge,
5000 rpms no surge.
Test performed while the car was out of gear and I only held it at higher rpms for about 5 seconds.

Makes me start to think this is fluctuating air flow. What if I pull the cap off the AFM and watch for fluctuations in the flap. If I do and the flap continues to cycle with the surges do you think there is enough of a delay in the flap opening to tell if it is caused by the surge or is causing the surge. Or can the computer be sending fluctuating signals at lower rpms and then not sending bad signals at higher rpms? I am holding the throttle open what does the computer control that could fluctuate rpms: does it close the AFM or Close something in the throttle such as the TPS (although it surged with the TPS disconnected)

Last night in bed (I think I'm starting to dream Porsche - and not in a good way) I decided that the injectors must be performing well otherwise it would probably not start or run at all, too important at 1000 rpms for there to be much that an injector cycle could do to affect surging. It seems the easiest culprit is still the DME giving bad idle message or the airflow is inconsistent.

Sorry for not doing the above test sooner, last thing I want to do is give you poor information to help me diagnose. And Thanks again for hanging in there to help.
Brad