1991 Caprice 5.0l hard starting in the AM

[WyrTwister]

This was Mom & Dad's car , that I inherited . Rarely driven , ~ 46,000 miles on it .

I have replaced the fuel pump when it went out . And fuel filter .

Takes a lot of cranking when cold , in the AM . Runs fine after that & for the rest of the day .

I replaced the fuel pressure regulator & that did not help .

Ideas , please ?

Thanks ,

 

[oldoak2000]

are you pumping the petal to the floor 2 or 3 times before cranking? then leave pedal at rest
the OLD cars (non computer/injected) require this as standard starting practice ....

 

[maxdustington]

Originally Posted by oldoak2000
are you pumping the petal to the floor 2 or 3 times before cranking? then leave pedal at rest
the OLD cars (non computer/injected) require this as standard starting practice ....
1991 would be a 305 TBI, so it would not require priming like a carbureted car would.
Check you fuel pressure when cranking to rule out the fuel system to that point. It sounds like it is losing pressure over night. Have you tried multiple fuel pump primes before cranking?

 

[umungus1122]

Definitely check if the pressure drops while sitting for a while (overnight or longer). Is it throwing any codes?

 

[ragtoplvr]

Fuel hoses that old often become porous. There are hoses inside the tank. As stated, check your fuel pressure before cranking or

Turn on key. wait 2 seconds.

Turn off key wait

repeat 3 times. This will prime the fuel pump (I think)

Then start it. If it cranks less, you have confirmed low pressure.

Rod

 

[clinebarger]

Sounds more like the Fuel Pump relay has given-up, These cars have a relay bypass built into the oil pressure switch......Once oil pressure builds to over 4 psi, It will send power to the fuel pump.

Locate the Fuel Pump "Prime" Connector (Red wire with a black plastic end on it) located near the fuel pump relay, It won't be connected to anything & it's sometimes taped to the outside of the harness.

Start the engine. If the relay is operational....There will be NO power present at the Prime Connector!
*If it does have power, The relay is faulty or you have a wiring issue, Along the outside chance of a faulty ECM.
*Don't bother checking fuses as the power for the fuel pump comes from the same fuse regardless of the switch being used.

 

[StevieC]

I would try priming it with key in the on position but don't crank, then off, then on to the same position. Do this a few times and then attempt to crank it over. If it starts easier then it's the fuel pressure leaking down over time and it's why the rest of the day it's fine and only affected by longer periods of sitting.

If that doesn't fix it then I would investigate somewhere else.

 

[WyrTwister]

Originally Posted by maxdustington
Originally Posted by oldoak2000
are you pumping the petal to the floor 2 or 3 times before cranking? then leave pedal at rest
the OLD cars (non computer/injected) require this as standard starting practice ....
1991 would be a 305 TBI, so it would not require priming like a carbureted car would.
Check you fuel pressure when cranking to rule out the fuel system to that point. It sounds like it is losing pressure over night. Have you tried multiple fuel pump primes before cranking?


You are 100% correct , 5.0l TBFI . Two big injectors in what looks a little like an old 2 barrel carburetor . Pumping the accelerator does not make a difference .

I agree , I figure it is bleeding down fuel pressure , why I replaced the fuel pressure regulator in the TB . Does the fuel pump have a check valve or foot valve in it ?

Thought about checking fuel pressure , but as far as I can tell , the solid fuel line screws directly into the TB . No Schrader valve or other user friendly way to attach a pressure gauge ?

I have tried turning the ignition key off and on , multiple times to try to prime it . Does not seem to help .

I think the fuel system is suppose to turn the fuel pump on for a few seconds , when you turn the key on , and then time out . There is ( I think ) an oil pressure switch , that maintains power to the fuel pump or fuel pump relay , when it senses good oil pressure . And keeps the engine running .

I figure this is a safety measure . If the oil pressure drops below a preset amount , the fuel pump quits and the engine soon runs out of fuel and dies .

 

[WyrTwister]

Originally Posted by umungus1122
Definitely check if the pressure drops while sitting for a while (overnight or longer). Is it throwing any codes?



It is OBD I , but no , no codes . Have not figured out a practical way to check fuel pressure . No Schrader valve . No fuel rail , hard metal pipe / line to the TB .

 

[WyrTwister]

Originally Posted by ragtoplvr
Fuel hoses that old often become porous. There are hoses inside the tank. As stated, check your fuel pressure before cranking or

Turn on key. wait 2 seconds.

Turn off key wait

repeat 3 times. This will prime the fuel pump (I think)

Then start it. If it cranks less, you have confirmed low pressure.

Rod



Tried cycling the ignition key . Does not seem to make any difference . :-(

 

[WyrTwister]

Originally Posted by clinebarger
Sounds more like the Fuel Pump relay has given-up, These cars have a relay bypass built into the oil pressure switch......Once oil pressure builds to over 4 psi, It will send power to the fuel pump.

Yes , I discovered this , looking at the wiring schematics .

Locate the Fuel Pump "Prime" Connector (Red wire with a black plastic end on it) located near the fuel pump relay, It won't be connected to anything & it's sometimes taped to the outside of the harness.

Yes , I used this when I was diagnosing the failed fuel pump .

Start the engine. If the relay is operational....There will be NO power present at the Prime Connector!

OK , with the engine running , check from the priming connector to chassis ground ? If the relay is good , zero volts at the priming connector ?

*If it does have power, The relay is faulty or you have a wiring issue,

So if 12 volt + is present at the priming connector , then what is happening is the oil pressure switch is supplying 12 volt + to run the fuel pump . After the engine has cranked sufficiently to build up good oil pressure ?

Would be nice if it is just a bad relay . I have no problem with replacing it .

Along the outside chance of a faulty ECM.

Never considered a faulty ECM . Engine runs fine after it starts .

*Don't bother checking fuses as the power for the fuel pump comes from the same fuse regardless of the switch being used.


I have noticed the exhaust smells rich , until the engine warms up .

I have considered the 2 injectors may be leaking down over night . I ordered 2 rebuilt injectors , but have not swapped them out , yet .

The car starts normally , all day long , after the initial startup . If it was a bad relay , does that mean the engine is maintaining sufficient pressure to satisfy the oil pressure switch , all day long ? Vehicles I have owned in the past , that had real oil pressure gauges , the pressure appeared to drop to zero , soon after the engine was turned off .

Thanks ,

 

[WyrTwister]

Originally Posted by ragtoplvr
Fuel hoses that old often become porous. There are hoses inside the tank. As stated, check your fuel pressure before cranking or

Turn on key. wait 2 seconds.

Turn off key wait

repeat 3 times. This will prime the fuel pump (I think)

Then start it. If it cranks less, you have confirmed low pressure.

Rod



https://www.rockauto.com/info/22/SP10H1H_TOP_P04__ra_p.jpg

Think this photo shows the only rubber fuel hose in the tank . It was replaced when I replaced the fuel pump .

Thanks ,

 

[WyrTwister]

The car has not been started in at least 6 months . Put the battery charger on it . Think I hear the fuel pump running when I turn the key on .

Will report back when the battery is charged & I try to start it .

 

[WyrTwister]

Let the battery charge 1 - 1-1/2 hours on slow charge . Started w/o too much cranking . Going to let it run for about an hour to bring the battery up to full charge & the engine up to operating temp .

This is probably a dumb question . It has a Bosch ABS system . I can hear the sound like a small electric motor breifly running when I turn the key on . Is that the ABS or the fuel pump ?

 

[StevieC]

It could also be the Ignition Control Module or Distributor Pick-Up coil not functioning correctly when it's cold but the warmth of the engine makes it functions correctly at that time. I believe the injector pulse is driven off this signal.

Something to check is to see if the injectors are pulsing in the throttle body when cold cranking.

 

[clinebarger]

Originally Posted by WyrTwister

OK , with the engine running , check from the priming connector to chassis ground ? If the relay is good , zero volts at the priming connector ?

With a Test Light or DVOM hooked to ground.

So if 12 volt + is present at the priming connector , then what is happening is the oil pressure switch is supplying 12 volt + to run the fuel pump . After the engine has cranked sufficiently to build up good oil pressure ?

Correct

Never considered a faulty ECM . Engine runs fine after it starts .

ECM Output Drivers do fail, But it's quite rare for the fuel pump relay driver to fail



I have noticed the exhaust smells rich , until the engine warms up .

I have considered the 2 injectors may be leaking down over night . I ordered 2 rebuilt injectors , but have not swapped them out , yet .

The car starts normally , all day long , after the initial startup . If it was a bad relay , does that mean the engine is maintaining sufficient pressure to satisfy the oil pressure switch , all day long ? Vehicles I have owned in the past , that had real oil pressure gauges , the pressure appeared to drop to zero , soon after the engine was turned off .

Thanks ,


The fuel system maintains residual pressure for a few hours. And a stone cold engine needs more fuel to start as well.

 

[WyrTwister]

Originally Posted by clinebarger

OK , with the engine running , check from the priming connector to chassis ground ? If the relay is good , zero volts at the priming connector ?

With a Test Light or DVOM hooked to ground.




Got you ! That was what I understood you were saying .

Got the battery charged yesterday & car started . Let it idle for about 1 - 1-1/2 hours to let it fully charge & warm up 100% .

( By the way , seems to take a long time to warm up . Can not remember if I have replaced the tstat ? )

Weather permitting ( rainy today ) I will check the priming connector with my Fluke .

Thanks ,

 

[umungus1122]

"I have noticed the exhaust smells rich , until the engine warms up."- Oh absolutely, until the oxygen sensor gets hot. Nothing like newer vehicles. They do take a decent amount of time to heat up fully. It takes me about 10 minutes of light driving to get hot enough for the stat to open at around freezing. I keep the radiator mostly covered up in the winter on my truck which has a 180 degree stat

 

[WyrTwister]

Tried to do some more checking on the Caprice , late yesterday ( getting dark ) . Not enough charge left in the battery .

This afternoon , pulled the company truck up close to the Caprice . Wan a jumper wire from the battery + to the red priming connector . Drew a small arc , so I interpenetrated that to mean the fuel pump was working .

Boosted it off . Had to crank it quite a bit , so I guess I did not succeed in priming it with the jumper wire . With the engine running I tested the priming connector with my Fluke , to battery - . No voltage .

According to what I have been told , that means the relay is working ?

Left the Caprice running while I went to the Dollar store & the Water Mill Express ( water $ .25 a gallon ) , ig I need to add some to the battery . Shut the car off when I returned .

No conclusion as to the reason for the long cranking .

 

[StevieC]

Check the ignition module by seeing if the injectors are pulsing in the thottle body on cold cranking. Also look for spark from a grounded wire while cranking.