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Nate
Nate, ASE Master Certified
Category: Buick
Satisfied Customers: 281
Experience:  ASE master certified GM master certified
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1994 buick roadmaster: 5.7L LT1..fuel delivery..fuel pump

Customer Question

I have a 1994 buick roadmaster 5.7L LT1 with a fuel delivery problem. Just replaced fuel filter and the fuel pump is working.

Any suggestions where to look next?
Submitted: 2 years ago.
Category: Buick
Expert:  Nate replied 2 years ago.
Hi, My name is Nate
I will do my best to answer your question as quickly as i can with the information you have provided. Thanks for visiting JA!

What is your fuel pressure reading? If you don't have enough fuel pressure, It could cause this problem. Have you checked the pressure with a gauge?

Customer: replied 2 years ago.

Hi Nate,

 

Don't have a gauge to check with, but when I press the relief valve on the fuel rail it sprays pretty strongly.

Customer: replied 2 years ago.

Could this be a pressure regulator issue?

 

Expert:  Nate replied 2 years ago.
Yes it could also be a regulator issue. First let me know what the key on engine off pressure is. One thing you could try is turning the key off and back on a few times (without starting the vehicle). This primes the fuel system for the highest pressure. Then try to start the car. It might work, it might not.... let me know
Customer: replied 2 years ago.

As I said, I don't have a fuel gauge to check pressure. When opening the pressure relief valve it seems to have pretty good pressure.

 

Have tried turning ignition on/off several times to build up pressure to try getting it to start with no luck.

 

 

Customer: replied 2 years ago.
Could this be an electrical problem with the injectors?
Expert:  Nate replied 2 years ago.
from what you are describing, I would say to check the fuel pressure first. You can check to see if there is power at the fuel injectors but you will need a noid light to see if the computer is sending the right signal to you injectors. Here is a link the fuel pressure gauge you will need (or something similar). I would suspect that the problem is the fuel pump or the regulator but without knowing the fuel rail pressure there is no way to know.
Customer: replied 2 years ago.

Hi Nate,

 

Pressure is fine.

 

Got a noid light and found out there is NO signal to the injectors. Any suggestions??

Expert:  Nate replied 2 years ago.
Ok....what was your pressure reading? Check and make sure you have power at the pink wire at all of the injectors. The power comes from the two "FUEL INJ" fuses in the under hood fuse block. Also check to make sure all the other fuses are good. Does the service engine light come on when you turn the key on? This would indicate the computer (ECM) is working correcly. let me know what you find.
Customer: replied 2 years ago.

All fuses are good.

 

Injectors are getting an intermittent signal. The noid light shows that the signal is not always there. (not a normal pulsing like I would expect)

 

Check engine comes on.

 

Could this be a bad ground somewhere?

Expert:  Nate replied 2 years ago.
Is the power constant while cranking? the ground comes directly from the ecm. also check all grounding points to make sure there is a good connection. It could possibly be a faulty ecm if all the connections, power and grounds are ok.
Customer: replied 2 years ago.

Power is constant (although it does vary slightly - 0.04 volts change max )

 

Will check ground next.

Expert:  Nate replied 2 years ago.
The ground is what is turned on and off by the ecm. connect one end of the noid light to battery power and the other end to the injector ground. does the light still cut in and out? Does the service engine light stay on steady while cranking (also controlled by the ecm)? check all the power and ground circuits to the pcm that would be the next steps.
Customer: replied 2 years ago.

Tried starting fluid again and now there is NO ignition as well as the intermittent injector signal.

 

Bad ECM?

Customer: replied 2 years ago.

Where is the PCM located?

 

Expert:  Nate replied 2 years ago.
Sorry for the delay....Here is the pcm location. Are you sure it's not the voltage dropping off? That could possibly be a bad ignition switch.

graphic
Customer: replied 2 years ago.

Thanks, XXXXX XXXXX is the ECM located?

 

Just need to know so I can check the various connections.

Expert:  Nate replied 2 years ago.
The ECM (Engine control module) is often times referred to as the PCM (Powertrain Control Module). In this application it is referred to as the PCM but it refers to the same module that controls the engine.
Customer: replied 2 years ago.

Hello,

 

So on this particular engine the ECM and PCM are the same unit. Is that correct?

 

And it is located underneath the air filter box, correct?

Expert:  Nate replied 2 years ago.
Yes that is correct.
Customer: replied 2 years ago.

Hi Nate,

 

Got it out.

 

Check for a replacement at the auto parts store and found out none of them carry it anymore.

 

Found a possible used replacement at a salvage yard. The possible replacement is in a 1994 Checy Caprice with an LT1. Should the computer from the Chevy be compatible with the Roadmaster fom the same year (and with the same engine)??

 

Thanks

Expert:  Nate replied 2 years ago.
I would think that would be compatible. The salvage yard should be able to tell you. As long as it is the same engine and model year you should be good. Just make sure you double check for any loose or broken grounds anywhere in the engine compartment or at the rear of the cylinder heads. Also check to make sure you have voltage at all of the pcm fuses with the key on.
Customer: replied 2 years ago.
Got it thanks, XXXXX XXXXX you know if it works out.
Expert:  Nate replied 2 years ago.
Please do, I'll be here to help you if you need more information.
Customer: replied 2 years ago.

Hi again,

 

Swapped the ECM still no luck.

 

Do you have a wiring diagram you could share?

Expert:  Nate replied 2 years ago.
Here are a few diagrams to help you test the power and ground circuits as well as the injector circuits. i can try to find more if you need them.

graphic

graphic


graphic
Customer: replied 2 years ago.

Hello,

 

Just checked the ignition system by pulling a plug to check for spark. No ignition spark was noted.

 

Any suggestions? (Checking grounds now.)

Customer: replied 2 years ago.

Checked for spark at coil and found no spark.

 

Igition control module problem???

Expert:  Nate replied 2 years ago.
Sorry for the delay in response. If you have no fuel and no spark then that is a different story. I figured you had spark before because it started and ran when you used starting fluid. The one thing that triggers the fuel injectors and the ignition system is the crankshaft position sensor which is integrated in the distributer on this car. If you had a good scan tool you could hook it up and see if the crankshaft position sensor was sending a signal the pcm. You could also check this with a lab scope but a typical multimeter doesn't have a quick enough sample rate to see this kind of signal. Distributer sends the crank signal to the pcm which triggers the ignition coil and the fuel injectors. I would suggest that either you get some test equipment or just simply replace the distributer. The distributer would be my guess but i wouldn't be 100% sure without proper testing.

graphic
Customer: replied 2 years ago.

Thanks Nate, I figured that was the case.

 

Funny thing is there was spark when the problem first appeared, but when I tried starting fluid again I got nothing. As I said, now there is nothing to the injectors and no coil response.

 

Based on the diagrams (and some research) I figured it was likely the OptiSpark system.

 

From my research I found that waterpump failure can cause failure in the optispark system (distributor behind the waterpump). I just bought this car 2 months ago and the guy I bought it from had had the water pump replaced a few months before due to it leaking.

 

Thanks again, will let you know how that goes. It is going to take a few days because no one carries that part locally anymore.

 

 

Expert:  Nate replied 2 years ago.
The fact that you had spark but no fuel at first is what confused me. It all clicked when you said you didn't have any spark either. Here are the instructions for replacing the distributer. Let me know if you need any more help!

  1. Disconnect negative battery cable
  2. Disconnect IAT sensor harness connector
  3. Remove air intake duct
  4. Remove serpentine drive belt
  5. Drain engine cooling system
  6. Disconnect three water pump hoses


Water Pump Removal


  1. Remove water pump assembly


Torsional Dampener Removal


  1. Remove crankshaft torsional damper
  2. Remove belt tensioner
  3. Remove spark plug secondary cables from distributor. Twist boot 1/2 turn and pull only on the boot to remove wire from distributor.
  4. Disconnect four terminal PCM connector from distributor.


Distributor Assembly Mounting


  1. Remove three distributor mounting bolts. Pull distributor forward until drive shaft disengages from engine. Mark the top surface of the shaft to denote location during reassembly.
Install or Connect:


  1. Install distributor shaft into distributor, if removed. Turn shaft until the mark is on top.
  2. Place distributor and shaft assembly into engine.
  3. Tighten three distributor bolts
Torque Value: 11 N-m (8 lb.ft.)
  1. Connect four terminal PCM connector to distributor
  2. Connect spark plug cables to distributor
  3. Install belt tensioner
  4. Install crankshaft torsional damper to engine
  5. Connect coolant temperature sensor connector
  6. Install water pump
  7. Connect three water hoses to water pump
  8. Fill engine with coolant


Serpentine Belt Routing


  1. Install serpentine drive belt
  2. Install air intake duct
  3. Connect intake air temperature (IAT) sensor connector
  4. Connect and tighten negative battery cable
Torque Value: 15 N-m (11 lb.ft.)
Customer: replied 2 years ago.

That's what confused me at first. There was spark but no fuel at fist. Now neithr works correctly.

 

 

Thanks again, will let you know how it goes.

Expert:  Nate replied 2 years ago.
Yes, please let me know how it works out.
Nate, ASE Master Certified
Category: Buick
Satisfied Customers: 281
Experience: ASE master certified GM master certified
Nate and 5 other Buick Specialists are ready to help you
Customer: replied 2 years ago.

Hi Nate,

 

Thank you very much. It was definitely the distributor.

 

She's running fine now. Excellent answers.

 

 

Matthew V.

Expert:  Nate replied 2 years ago.
That's great news! Glad you got it fixed!

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