I recently acquired a 1988 Ford Thunderbird with a 3.8l v6 with 65,000 miles from my wife's grandparents. Upon receiving the vehicle, it had not been started for at least 2 years (that we know of) and it would crank but never start. So, after seeing that it would not start I replaced the spark plugs, spark plug wires, fuel pump, fuel pump relay, battery, alternator, and belts. After replacing everything it fired right up and ran pretty well except for the fact that it randomly acts as if it's running out of fuel at idle or up to speed. I have put a fuel pressure gauge on the rail and on turning the key it shows 40psi, at idle it's about 32psi, however when I give it a little bit of gas for a few seconds it drops to 25-27psi and then the gauge jumps between 30-34psi after I let off the gas. Is it normal for the pressure to drop that much when I am barely pushing on the gas in park? Any help or suggestions would be appreciated.
88 Ford Thunderbird Fuel Pressure Issue?
- Thread starter TFBird
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Yup, there's a vacuum regulator that messes with pressure slightly bases on intake vacuum.
While messing with it, pull its vacuum line and see if that makes your pressure rock solid. Also check for fuel in that line; sometimes the diaphragms rupture on these.
While messing with it, pull its vacuum line and see if that makes your pressure rock solid. Also check for fuel in that line; sometimes the diaphragms rupture on these.
Vacuum regulator? Would that be the fuel pressure regulator?
OVERKILL
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Originally Posted By: TFBird
Vacuum regulator? Would that be the fuel pressure regulator?
Yes, it has a vacuum line on it to reduce fuel pressure under low load (high vacuum) conditions.
Vacuum regulator? Would that be the fuel pressure regulator?
Yes, it has a vacuum line on it to reduce fuel pressure under low load (high vacuum) conditions.
I will check that out first thing tomorrow, would it be possible that the fuel pressure regulator would cause random stalling/loss of power? sometimes it's fine for 30-40 minutes of driving at 50+ mph then all the sudden the engine jumps and acts like it's out of fuel. Once it starts it keeps jumping and feeling sluggish until i stop for a few minutes or turn the engine off. after this happens the engine fires right up and it's good again for 10 minutes or so.
OVERKILL
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Originally Posted By: TFBird
I will check that out first thing tomorrow, would it be possible that the fuel pressure regulator would cause random stalling/loss of power? sometimes it's fine for 30-40 minutes of driving at 50+ mph then all the sudden the engine jumps and acts like it's out of fuel. Once it starts it keeps jumping and feeling sluggish until i stop for a few minutes or turn the engine off. after this happens the engine fires right up and it's good again for 10 minutes or so.
That sounds like the fuel filter or the sock on the fuel pump is getting plugged up with crud.... A buddy of mine had the same problem with his Mustang and it was sediment in the tank that plugged the sock.
I will check that out first thing tomorrow, would it be possible that the fuel pressure regulator would cause random stalling/loss of power? sometimes it's fine for 30-40 minutes of driving at 50+ mph then all the sudden the engine jumps and acts like it's out of fuel. Once it starts it keeps jumping and feeling sluggish until i stop for a few minutes or turn the engine off. after this happens the engine fires right up and it's good again for 10 minutes or so.
That sounds like the fuel filter or the sock on the fuel pump is getting plugged up with crud.... A buddy of mine had the same problem with his Mustang and it was sediment in the tank that plugged the sock.
I did change the fuel filter a couple of times after I ran some bg 44k in it. I have not checked the strainer on the fuel pump since I installed it though. After he cleaned the strainer did everything go back to normal?
The fuel pressure is dropping to low, was there any rust in the tank at all? If no rust or other debris in the tank either the new pump is junk or you are losing power or ground. If the regulator failed the pressure would be high or fuel would be coming out of the vacuum port for the regulator.
I used to own an '88 Cougar (same as the T-bird) with the same 3.8 that you have. I managed to get 300K miles out of it without taking off a valve cover or the oil pan. However, I did replace the fuel pump several times. (Along with the alternator and a few water pumps)
If it was mine, I think I'd replace the fuel pump just for a little peace of mind and troubleshoot after that.
If it was mine, I think I'd replace the fuel pump just for a little peace of mind and troubleshoot after that.
I did check the voltage from the positive terminal on the battery to as many grounds as i could find and they all tested at 12.6v while it wasn't running and 14.8v while idling. there wasn't any noticeable debris in the gas tank however after i put the 44k in the first time the fuel filter clogged up within a week with black sandy substance. maybe the 44k scrubbed stuff off of the gas tank? The fuel pump on there is only a month old. Next time I run the tank down i'll drop it and see what the strainer looks like. Is there anything else that I should look at while I have the tank down? Should I put a multimeter on the harness going to the fuel pump? Could the harness go bad?
OVERKILL
$100 Site Donor 2021
Originally Posted By: TFBird
I did change the fuel filter a couple of times after I ran some bg 44k in it. I have not checked the strainer on the fuel pump since I installed it though. After he cleaned the strainer did everything go back to normal?
Yes. Once we got the crud out of the tank and cleaned the sock the car was fine.
I did change the fuel filter a couple of times after I ran some bg 44k in it. I have not checked the strainer on the fuel pump since I installed it though. After he cleaned the strainer did everything go back to normal?
Yes. Once we got the crud out of the tank and cleaned the sock the car was fine.
If fuel pressure drops at WOT it has a restriction(filter, tank pickup, etc), or a weak pump... Pressure should maintain at 40 psi for however long you are brave enough to hold it at WOT... At idle it will be around 32 as vacuum applied to the regulator will be compensating for high manifold vacuum...
Easiest way to test is remove vacuum line to regulator, pressure will rise to 40 PSI, if it falls any at all during brief WOT it has delivery(fuel volume)issues...
If it's never had head gaskets plan on replacing them once it becomes a regular driver, just part of owning a older 3.8...
Easiest way to test is remove vacuum line to regulator, pressure will rise to 40 PSI, if it falls any at all during brief WOT it has delivery(fuel volume)issues...
If it's never had head gaskets plan on replacing them once it becomes a regular driver, just part of owning a older 3.8...
Originally Posted By: TFBird
I did check the voltage from the positive terminal on the battery to as many grounds as i could find and they all tested at 12.6v while it wasn't running and 14.8v while idling. there wasn't any noticeable debris in the gas tank however after i put the 44k in the first time the fuel filter clogged up within a week with black sandy substance. maybe the 44k scrubbed stuff off of the gas tank? The fuel pump on there is only a month old. Next time I run the tank down i'll drop it and see what the strainer looks like. Is there anything else that I should look at while I have the tank down? Should I put a multimeter on the harness going to the fuel pump? Could the harness go bad?
T properly measure voltage drop under load you connect one lead of a DVM to the plus on the battery and the other end to the plus on the device to be tested, while it is running. Measuring from the battery plus to ground is only going to measure the drop caused by current flow through the meter, which is in the microamp range for a good one.
I did check the voltage from the positive terminal on the battery to as many grounds as i could find and they all tested at 12.6v while it wasn't running and 14.8v while idling. there wasn't any noticeable debris in the gas tank however after i put the 44k in the first time the fuel filter clogged up within a week with black sandy substance. maybe the 44k scrubbed stuff off of the gas tank? The fuel pump on there is only a month old. Next time I run the tank down i'll drop it and see what the strainer looks like. Is there anything else that I should look at while I have the tank down? Should I put a multimeter on the harness going to the fuel pump? Could the harness go bad?
T properly measure voltage drop under load you connect one lead of a DVM to the plus on the battery and the other end to the plus on the device to be tested, while it is running. Measuring from the battery plus to ground is only going to measure the drop caused by current flow through the meter, which is in the microamp range for a good one.
I tested out the pressure again and disconnected the vacuum line, the PSI held at 40 no matter what I did on the accelerator WOT or anywhere in between it stayed at 40. I hooked the vacuum line back up and it dropped to 32psi and jumped around 31-33psi. So would this rule out any debris in the gas tank? Where should I look next?
OVERKILL
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Originally Posted By: TFBird
I tested out the pressure again and disconnected the vacuum line, the PSI held at 40 no matter what I did on the accelerator WOT or anywhere in between it stayed at 40. I hooked the vacuum line back up and it dropped to 32psi and jumped around 31-33psi. So would this rule out any debris in the gas tank? Where should I look next?
Yup, that rules it out unless the debris only gets there while you are moving. Are you able to make it stumble when it is stationary? You need to check the fuel pressure when it is demonstrating its "condition" so to speak.
I tested out the pressure again and disconnected the vacuum line, the PSI held at 40 no matter what I did on the accelerator WOT or anywhere in between it stayed at 40. I hooked the vacuum line back up and it dropped to 32psi and jumped around 31-33psi. So would this rule out any debris in the gas tank? Where should I look next?
Yup, that rules it out unless the debris only gets there while you are moving. Are you able to make it stumble when it is stationary? You need to check the fuel pressure when it is demonstrating its "condition" so to speak.
So I pulled my fuel filter and decided to take a look at it just to rule out one more thing and this is what came out of it... I guess after driving all this [censored] could get stirred up into the filter and clog it up.
Could this be the fuel line deteriorating?
OVERKILL
$100 Site Donor 2021
Doubt it, probably just crud in the tank coming off because of it sitting.
Just a story,
I had a 91 caddy with the 4.9
It would run perfect except for when accellerating heavy
(not when revving stationary)
more like... highway on ramp.
Turns out had a slightly crimped piece of copper fuel line.
So back on topic.. I'd check for restriction somewhere.
it might have no problem getting 40psi idling. but what about when the engine is actually using alot of fuel.
I had a 91 caddy with the 4.9
It would run perfect except for when accellerating heavy
(not when revving stationary)
more like... highway on ramp.
Turns out had a slightly crimped piece of copper fuel line.
So back on topic.. I'd check for restriction somewhere.
it might have no problem getting 40psi idling. but what about when the engine is actually using alot of fuel.
Okay, I'll just drop it and clean it when I get a chance. Looks like of like clay though.
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