Ht4100 failing fuel pump?

[Downtowncaddy]

Hello everyone.

I have an 83 eldorado with an engine that is acting very strange while under power.

Does anyone have any experience with a failing fuel pump on these engines?  If so, what were the symptoms and is this a common occurrence?

Thanks for your help.

Erik

[Gene Beaird]

Usually, a failing electrical fuel pump will show symptoms on startup. You turn the key on, wait for the pump to spin for three seconds and stop, and try to start the car. It won't unless you cycle the ignition a few times to get enough pressure in the lines. Sometimes, the pump can't keep up at WOT, but once you get the car started, it will usually, otherwise run well...... right up to the point the pump fails completely, and you're thumbing a ride home.

Clogged fuel filters will usually cause the engine to act like it's running out of fuel on moderate acceleration, or, at normal cruise, you have to drive at slower and slower speeds to keep the engine running.

What are your symptoms?

[Downtowncaddy]

Gene

Thank you for the detailed information on symptoms of a failing fuel pump.  Sadly it doesn't sound like my symptoms. The car pulses/surges while driving, to me it feels like it's not getting constant or enough fuel. Yesterday the car had alomst no power going up a vey slight hill.

I have changed the fuel filter and have put fuel injector cleaner in the tank and the problems are still there. 

Could this be something with the fuel injection system?

Thanks.
Erik

[Downtowncaddy]

Possible bad O2 sensor?

What would these symptoms be?

[76eldo]

You have throttle body injection so if you take off the air cleaner and run the engine and rev it while you are watching you can see the fuel coming out of the "injectors".  Way different from port fuel injection.

Could be almost anything.  How old are the plugs and wires?  The cap and rotor?  Could also be the electronic module or pickup in the distributor.

Is it pinging while losing power?  Have you checked the ignition timing?  Do you have a shop manual?

It's a methodical process of eliminating possible factors to figure it out.

Brian

[James Landi]

I did have an "in tank" fuel failure on my 83 Eldorado --- it happened at over 250,000 miles.  Car would simply not start. There were no tell-tail issues prior to failure.  I have read posts that a failing fuel pump makes an audible buzzing sound when the ignition is on. 

When your car is surging and losing power  an easy way to figure out if you have bad ignition parts is to simply tune your radio to the AM frequencies, and tune in around 1620-40 khz. you should hear an ignition whine that corresponds to rpm.  If you hear a popping on the radio, as you put the car under load, then you have bad ignition parts... (wires, cap, plugs)  Don't punish your 4100-- if it's not running well, you need to get it fixed.

[Downtowncaddy]

James and Brian

Thanks for your suggestions and tips, much appreciated.

I will look into these on Saturday, while I am replacing my O2 sensor.

I will keep you posted.

Regards
Erik

[Walter Youshock]

If it's running at all, it's a miracle...  I remember my '82 acted like this.  The ISC was opening and closing.

[Downtowncaddy]

Walter.

Thanks for the advice, however not being a car expert can you tell me what ISC stands for and how you can remedy it?

Erik

[76eldo]

Idle Speed Control Motor, looks like a solenoid resting against the throttle linkeage.

Generally when these go bad or are out of spec they will click about 10 times when you turn the car off.  They will also click as they are "hunting" for a set point while the car is idling which you can feel if you rest your foot on the gas pedal.

Probably not relevant to the problem you have mentioned.

A running issue like you describe can be:

1.  Fuel issue
2.  Ignition problem
3. Vacuum leak, a major one
4.  Mechanical issue like a bad lifter or worn cam gear that drives the distributor.

The shop manual will be helpful here.

Brian

[Downtowncaddy]

Brian

Thanks for the clarification on the idle speed control, and you are right those symptoms are not occurring on my car.

Hopefully this weekend I can do some more investigation.

Erik

[TJ Hopland]

I never understood why they didn't put some sort of fuel pressure test port on the TBI engines.   IF they did this would be a simple diagnosis, fuel pressure gauge and test drive.    I think GM had a fairly complex assembly that you connected to the throttle body then back to the fuel line that then had the test port for a gauge.   I never saw one in person, just in manuals.   Looked like a pain to install. 

One issue I have read about quite often in more recent years is that there is a short piece of hose between the pump and hard send line in the tank.  With age that piece of hose splits and leaks.   Its inside the tank so it basically just bypasses some of the volume and pressure back into the tank.    As the fuel line pressure changes the size of the leak changes.  Some demand situations the hole kinda closes up till the pressure rises then it opens again so the pressure tends to oscillate.   You also have a fuel pressure regulator that may or may not be working properly trying to regulate the pressure.   The engine management does not know what the pressure is, its just dealing or trying to deal with the results of the varying pressure by reading the O2 sensor.     At steady states like idle the pressure does not vary so things tend to stabilize.    Change the demands and conditions and it all starts to vary again.

Other issue that can give you those symptoms that was an especially big issue with the longitudinal 4100's for some reason was the distributor would get loose and out of time.   For a while the computer can compensate for it and mask the problem but without the correct base setting it tends to hunt for a happy place which it has more and more trouble finding the further it is off.  Just grab the top of the cap and see of you can turn the distributor in either direction.    The transverse engines didn't seem to have that issue so they must have changed something in the intake or block? where the mount and clamp was to get rid of that issue.   

[936CD69]

The distributor driven gears were prone to wearing (apple-coring) which could cause your problem. GM released a second design gear in the mid 80s. Good idea to check the cam drive gear as well if you pull the distributor

[Downtowncaddy]

Craig.

Thanks for the tip on the distributor. Someone very knowledgable in my caddillac club suggested the same thing to me.

I am working on the car for the next two weeks to get it more reliable / drivable for the summer months.

[Gene Beaird]

Pull the vacuum hose off the fuel pressure regulator and make sure the regulator hasn't failed. I would be looking (or smelling for) raw gas in the vacuum hose. It shouldn't be there. I had two different regulators fail on the same car (not a Cadillac).  Chased that problem around for a while, thinking I had already tested the fuel pressure. When I restarted my testing procedures again, I discovered the gas in the vacuum line when I pulled it off to test the fuel pressure.

It's a simple, quick test, and you can check it off the list early on. The regulator an still be bad, but a ruptured diaphragm is the most common failure mode.

[TJ Hopland]

Regulator is a good thought but on the TBI engines there is no vacuum line to remove and inspect.   Its built into the throttle body so there is an internal passage that gives it its vacuum signal.  They didn't even give us a fuel pressure test port on these things.   At this age a throttle body refresh kit is not a bad idea even if its not the issue.   The deluxe kit includes the regulator and all the O rings for the injectors.