# 94 Cutlass Supreme 3100 SFI V6 with pics, engine died abruptly



## justplumducky (Aug 7, 2009)

94 Cutlass Supreme 3100 SFI V6'
This engine is not the original, but owner says the original was also a 3100 SFI V6.
Engine stopped abruptly like key was turned off.

Owner put a timing light clamp on one of the cylinders and cranked the engine and had a steady light flashing pattern, if that's a good indicator of ignition spark.

Not my vehicle, but couldn't hear fuel pump running when key turned on. It had been a while (Not much help I know) since key was last tried so I suppose fuel pressure would bleed off after a while, then it should make the whine or humming noise when key turned on again I'm guessing.

Haynes Repair Manual said there's supposed to be a shraeder valve to hook up a fuel pressure guage, and to relieve fuel pressure first. Haven't had a chance to read book further yet - wanted to get this posted right away in hopes of suggestions. Will look further in book now. 

How do you relieve the fuel pressure exactly? I've identified the location of the fuel pressure regulator and traced the fuel line supplying it, but don't see a shraeder valve yet, unless it's down lower where I can't see it, and don't see it on the fuel rail running just above the injectors. I imagine it would be fairly accessible, but I don't see it. Maybe I've missed it.

We'll have to buy a pressure I guess if relay is not the problem I guess. I understand pressure guage needs to be approx 100 psi capable, not like the older cars I used to work on with mechanical fuel pumps.

Looking at the bottom of relay, there were three prongs along the longer side of relay and two on the opposite longer side of relay. The two prongs on opposite side were at each corner of relay body, if this helps any. Was hoping someone could tell me how to check the relay with ohm-meter and jumper wires. Sorry I didn't get a pic of the diagram on the relay. My memory of it is coming up short, but maybe I will find it online somewhere. I'll be looking. 

Thx much for any replies.


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## ron45 (Feb 25, 2014)

When you crank the engine is the top and bottom of motor both turning.?
Squirt starter fluid in the air intake at motor. If it starts/stalls....
Did you put your ear near the fuel pump when someone turn the key to on.?
Find another good known relay of same size and switch them.?
Check to see if juice is getting to the relay. If so run a jumper wire.?

It's late, come back and let us know..........


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## Windows on Wash (Aug 30, 2011)

There should be a test port very near the rail. Most time you can confirm that the pump is pressurizing via just listening for it though. 

Ron's suggestions should help you narrow it down to a fueling problem. Be sure to check the fuses and the relay for the pump too. You can just use the fuse as well to listen for the pump.


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## 47_47 (Sep 11, 2007)

Get a fuel pressure gauge on it first. Test port should be on the rail.

I copied this from the net:
On some older GM vehicles that use an oil pressure switch system, the vehicle will start by using a fuel pump relay to send power to the pump. Then after the ECM receives the appropriate signal from the oil pressure switch, the ECM de-energizes the relay allowing voltage to travel thru the oil pressure switch to the fuel pump. This occurs so when the engine dies and resulting oil pressure becomes low, the power is then cut off to the pump. If the oil pressure switch is faulty then, the power will be cut off to the pump when the ECM switches it over.

In some cases, the ECM is programmed to shut off power to the fuel pump if there is a loss of signal from the oil pressure switch on particular applications. This is a safety function used by the manufacturer to help eliminate any possible dangers created by fuel leaking on the scene of a vehicle wreck.


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## McSteve (Dec 8, 2009)

Ugh, I still have bad memories of that engine. The fuel pressure test port will be nestled in nice and cozy to the intake manifold, on the injector rail. Should have a black plastic cap on it.

To connect a fuel pressure gauge, I usually just wrap a rag around the area before screwing the hose onto the test port. You'll get a little fuel leakage if there's pressure on the system, but nothing major. If you prefer, it's easy to relieve the pressure first by pulling the fuel pump fuse or relay and cranking the engine for a few seconds.

Fuel pressure should be about 55-60 PSI for that engine, if I recall correctly.

As a quick and dirty test to make sure you're getting *any* fuel delivered, turn the key on and off a couple times and then depress the valve in the test port. You should get a pretty forceful spray of fuel.

If you can't hear the fuel pump when turning the key on and off, it's a safe bet that's your problem. If you can get at the fuel pump connector without dropping the tank, disconnect it and test for 12V while someone cycles the ignition key on and off. If you've got power, the fuel pump is shot. If there's no power at the fuel pump connector, work your way upstream; the next likely suspect is the fuel pump relay.

To rule out ignition and timing failures, you can feed it some starting fluid while someone cranks it. On the flexible air intake duct, close to the throttle body, you can pull out the black plastic PCV tube, leaving a convenient port to spray starting fluid into.

Take it easy with the starting fluid, and only spray while the engine is being cranked. Otherwise, it's likely to backfire through the intake, and ignite the pooled fluid, at which point you will have to extinguish the fire, patch the melted duct with electrical tape, and replace the scorched air filter. Ask me how I know...

If you smell a strong gasoline odor under the hood after cycling the ignition key a few times, check the fuel supply & return hoses near the rear driver's side of the engine. They were prone to leaking at the crimps on the 91 model year, but the replacement hoses I got in 2004 (Dealership part, over $100 for the pair, IIRC) were an improved design. I'm not sure when they made the switch.

If you want full electrical diagrams and the like, AlldataDIY is a pretty decent service. Some of the information is every bit as inaccurate as the Haynes and Chilton books, but it usually has good test procedures and diagrams.


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## 47_47 (Sep 11, 2007)

McSteve said:


> Ugh, I still have bad memories of that engine.


Don't know of anyone who's had good experience. We all ran and hid when those came in with drivability problems.


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## McSteve (Dec 8, 2009)

They've got a hard and fast expiration date, for sure. Once they decide they're done, no amount of diagnosis and new parts will bring them back. The genie comes out of the bottle and that's that. My Grand Prix was still my favorite car, though. So stable you could take a cloverleaf at 45 or so.


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## justplumducky (Aug 7, 2009)

Thank you guys for all the help! I think we followed a little (or more) advice from all who posted here...

*McSteve. posted:* Take it easy with the starting fluid, and only spray while the engine is being cranked. Otherwise, it's likely to backfire through the intake, and ignite the pooled fluid, at which point you will have to extinguish the fire, patch the melted duct with electrical tape, and replace the scorched air filter. Ask me how I know...

How did you know? :devil3: (thx much for that warning!)

Removed fuel filler cap and could hear nothing. Some started fluid in the intake, and engine ran for a few seconds, then died. New fuel pump relay installed and also new fuse (same fuse box under hood) for fuel pump relay circuit. No help. Found the test port (shraeder valve) " nestled in nice and cozy to the intake manifold, on the injector rail. Should have a black plastic cap on it." Thank you! I was concentrating too much on the other end of intake near the pressure regulator. Owner didn't want to buy a fuel pressure guage just yet, and neither did I cause we couldn't hear the pump running after installing new fuel pump relay and fuse. Have one, but is for the oldies... only up to 15 psi. 

I do have a '94 F-250 5.8 so I need to get one. It has some problems. Will be back one day. 

Today soon, we're gonna look for that electrical connection to pump underneath, near tank I assume, and check for voltage.


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## Bigplanz (Apr 10, 2009)

Harbor freight has a fuel pressure gauge for about $20. I have it. It works ok.
http://www.harborfreight.com/automotive-motorcycle/diagnostics/fuel-injection-pump-tester-92699.html


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## Windows on Wash (Aug 30, 2011)

Progress.

When it comes to fueling issues that are at the tank (i.e. pump side), they are more often failure than they are electrical issues. 

You will probably have to drop the tank to access it so be prepared for that.


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## Brainbucket (Mar 30, 2015)

Most fuel pump fails is of course age. But the electric fuel pump is cooled by the fuel going through it. No fuel, no cooling the pump. Low fuel can and running out of fuel does damage the pump. So that said be careful.:vs_cool:


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## WyrTwister (Jul 22, 2013)

I may be wrong , but my theory is the ethanol in the gas we get now , is hard on the fuel pumps in older cars . Probably not good on the rest of the system , too ?

I have had fuel pumps fail if the car had been setting un used for a year or two . On two cars .

I have seen , what I think , was a failure caused by the oil pressure switch turning off the pump circuit . But could not prove it . 

A friend told me this can happens , every once in a while , if an oil filter messes up & blocks oil pressure . Do not know about that either , but an oil filyer id a cheap thing to replace .

God bless
Wyr


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## justplumducky (Aug 7, 2009)

Indeed it was the fuel pump. Thx much for all the help :thumbsup:


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## WyrTwister (Jul 22, 2013)

Congrats ! 

God bless
Wyr


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