schip43

Sigh ... I've been MIA from here for a very long time! The issues with my 89 Turbos started a long time ago. Bad hydraulics, was the start. It would not go into gear with the motor running??? It ... turned out to be a blown Hydraulic line to the slave cylinder which I only found when I decided to pull out all the old crap and replace it with SS. I'll glaze over the part where the 951 tried to kill me when it fell off the 4 jack stands on a slanted drive way!! Damage done to fuel lines, steering rack boot and radiator shroud, Had to call a tow to get it into the garage!

Fuel lines were bad and replaced, then sigh ... no start?? So fuel replaced FP once twice three times maybe four don't really know?? I pulled the dme and klr not sure how to get that crap back in place but whatever. And still no start. I checked the Speed and Reference sensors with a DVOM for Resistance and .Voltage and I was sure they checked out to spec??? But I get no tach bounce and of course ... no start!

So simple question ... if I switch the ignition to on and put a 12 volt test light to the positive and negative wires at the fuel pump harness wires... it should light correct?? The Speed and Reference harness has been replaced but it would still do occasion, no hot start at random when it ran ... many,many years ago. I'm tired of chasing my tail and I need help ... apparently.

V2Rocket

Fuel pump doesn't turn on until you are cranking with the key.

Just turning ignition on doesn't automatically run the pump

GPA951s

the obvious first question i did you replace the actual DME Relay? The next one is do you know for a fact that you are not getting FP? If the actual DME Relay is bad that could cause no tach bounce as well.. If you really think that its the FP AFTER you know you have a good DME Relay, Then get about 15 FT of wire, Hook one end to the FP and "Bump: the engine for the FP to turn on... see if you get voltage... If you have a good DME Relay and you have FP, then check spark... As for as the reference sensors, PM "Amagamatedtom He has a great tool to check them. (carmonica)" The tool is 125 bucks and well worth the money. I just purchased one myself just to have. and I dont even have any issues with my cars right now. You must trouble-shoot and and start eliminating things vs just shotgunning parts... Do some testing and get back to us and we can help you further.

Humboldtgrin

You can pop the cover off the relay and manually push the relay contact. Sometimes with these fuel pumps if they sit for a while they tend to not want to work. I used a rubber hammer and tapped the fuel pump cover on my 86 944 beater to get it going a couple times after it sat for a while. Not recommend but it worked. Also no tach bounce is a whole other issue or so I thought. You may have bad or corroded grounds, switches, relays, DME/KLR, broken wires, maybe the wrong gap for the speed reference sensors, then there is fuel that turned to turpentine if it has sat for some time.

schip43

Well that sounds like exactly like the kind of PIA thing I suspected!?? But I am a "Pro" at doing "the same thing over and over again and expecting a different result ..." So far that has not worked out so well.

Humboldtgrin

That’s called insanity.

markl951

You can make the fuel pump run without the key by first removing the DME relay and then jumpering circuit 30 (Battery) to circuit 87b. You just need some blade style crimp terminals that fit down in the socket where the DME relay goes. Make sure the jumper wire can handle 10A. #16 AWG will do. Put a fuse in series just to be safe.

schip43

LOL ... I skipped over a whole lot.
But "ZERO" chance of "flat gas." The original gasoline from uh many,many years is long gone! That happened when I drained the original gasoline after replacing the spewing OEM, worn out lines. That was exciting but hey no fire.

The OEM fuel pump that (was the first fuel pump Replacement!!!) I promptly dropped on the ground and bent the positive terminal!! And thus it begins! That fuel pump did not work?? Fuel Pump two did not work?? I think I then bought a third if not a forth FP?? I have no idea which one is in there now but it's not working in any case?? Sooo yeah

And when I thought I was ready to try again with new gas. That is when I found another bad fuel line?? I had poured new gas in and it poured right out?? I assumed it was something I had touched?? But nope this was a new issue?? The really short line that comes from the tank to the fuel filter was soft swollen and leaking?? It looked fine but it was shot! That was the second gasoline bath!

Sigh, I got that replaced and with what had to be the first replacement fuel pump I tried to start it again and I got nothing???

schip43

Hmm OK I tried 87b and 30 and still got nothing?? But then I saw this ...

http://rennbay.com/DME-Relay-Info.html

I still got nothing?? But what is the correct way to by pass the stupid thing?? All I know for sure, is that I do not have power at the fuel point terminals ... I got nothing there??

schip43

The DME Relay?? Yep that is a great basic question! I'm the third owner of this 89 951 and when I got it from my best friend, the first thing he said was the DME Relay ... you have a spare.

So when the first "no start happened" I swamped it with the spare and it made no difference?? So then I tried to jump it pin's 87 and 30. That seemed to make no difference either?? So I'm pretty sure I just put the original DME Relay back in place??

The original Speed and Reference Sensors have been replaced as well as the original harnesses to them. Even so it when did run ... I was having the occasional hot restart, no start issue??? If the tach don't bounce .. the car won't start ... apparently?

I did check the resistance and the AC Voltage at the DME. But hey maybe I tested it wrong??? And I know I have Zero FP. AS I also replaced ... added the Pauer Tuning SS fuel Lines with the on board FPG. Zero Fuel Pressure ... to this day.

But hey maybe I screwed up the trouble shooting with the DVOM?? Soo I kept buying and replacing fuel pumps. Made no difference ...surprise.

But yeah this crap is getting old ... I saw the Carmonica and I have set a deadline ...finally! If I can't get to start by Friday ... I will order one! Cuz I am not touching those things If I don't have too!! I really want to rip all that crap out and go with a standalone ... but really If you can't make it start when it should, that (Standalone) could make things worst???

schip43

Aww well so "they say." But how do you know ..until you try?? But yep .. it seems to be true, ie how many fuel pumps are you gonna buy??? Three ..does not seem to be enough??? But hey many four will work??

GPA951s

OK Zero Fuel Pressure... Get some wire.... Attach one end to the + on the FP.. (Alligator clip or whatever) and Run that wire up into the cabin of the car.. Attach a test Light to it, Or Better Yet a Voltage Meter. You can pick up the ground on the Door ( That's usually what I ground to) because its EZ to clip on the flat damper thing) Hit the Key... See if you have 12V at the pump.. If you do and still no pressure... Then Switch the clip from the + terminal on the FP to the - terminal and take your meter and see if you have Zero Ohms to Ground. If you do... then its another bad FP..

I always test my Pumps before I put them in. Another "Quick" way is.. If you have an assistant you can just bump the key while their hand is on the pump to confirm that is Buzzes...

CyCloNe!

I thought when you had a test light or multimeter to the fuel pump plug with the ignition on it should read 12v even though it’s not pumping? Years ago I found out mine was bad and I remember trying this but can’t remember if this worked. Which if theres 12v at the plug that lets you know the circuit is working so would point to the pump.

markl951

The DME computer prevents any voltage from getting to the fuel pump unless it detects that the crankshaft is turning (speed sensor feedback). That's what the DME Relay is for.

If you jumper 30 and 87b and the fuse panel DME socket like I said then you are bypassing the protection circuit of the DME computer and directly applying 12V to the fuel pump. If you put that jumper in and don't measure 12V at the fuel pump then you have an open circuit in the wiring somewhere. Measure the voltage back near the fuel pump w/o the wires connected to the fuel pump as the first step to make sure 12V is getting all the way back there. If you have 12V but it won't run the pump you might have a bad ground which can limit the current you need. The pump needs about 10A. With the pump connected, what voltage to you read across the pump terminals when 30 and 87b are jumpered? If it's less than 12V that might be your problem.

Do you have a know good jump box? Connect that directly to your fuel pump. If the pump doesn't run then you probably have a bad pump.

The circuit Travis shows on his Rennbay site is how you can bypass the DME Relay and start the engine. It's a "get you home" sort of fix but it forces all the current to go through the ignition switch which is not a great idea as a long term solution.

CyCloNe!

Ok I probably used the jumper when I did it.... been a long time. The jumper was a huge help back in the day lol.