This was a big clue:
Engine bogs down when accelerating
Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 1
From: South Florida
Engine bogs down when accelerating
Hi all,
Really stumped with an issue and I've done all the research getting nowhere. By way of background, bought an 87 that was non running and sat for a very long time. Drained the very old gas, put in a new pump/assembly and found out the engine had a knock. Replaced with an 88 and have been driving it. I was having a brake issue and just fixed when this new issue pops up.
Start the car and it takes a couple of cranks but starts fine. Around 30 psi. Drive it and for the first 20 to 30 seconds its fine. Then it will start to bog down. Giving it gas has no effect and it'll putter and back fire then eventually get to speed but if you give it more gas it'll bog down again. Psi drops to 20 at idle when warm. When driving, psi will drop as low as 10 on acceleration. Replaced the pump, pressure regulator, egr, filter with zero results. Upon taking out the old filter, there was a TON of gunk in there and the filter maybe has 100 miles on it. At this point I'm completely lost on what it could be. Car had zero issues before this and its completely spontaneous.
Really stumped with an issue and I've done all the research getting nowhere. By way of background, bought an 87 that was non running and sat for a very long time. Drained the very old gas, put in a new pump/assembly and found out the engine had a knock. Replaced with an 88 and have been driving it. I was having a brake issue and just fixed when this new issue pops up.
Start the car and it takes a couple of cranks but starts fine. Around 30 psi. Drive it and for the first 20 to 30 seconds its fine. Then it will start to bog down. Giving it gas has no effect and it'll putter and back fire then eventually get to speed but if you give it more gas it'll bog down again. Psi drops to 20 at idle when warm. When driving, psi will drop as low as 10 on acceleration. Replaced the pump, pressure regulator, egr, filter with zero results. Upon taking out the old filter, there was a TON of gunk in there and the filter maybe has 100 miles on it. At this point I'm completely lost on what it could be. Car had zero issues before this and its completely spontaneous.
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
You might just take a look at the new fuel filter you installed as you might find it full of gunk also. If so, the tank would need to be cleaned. I went thru this once with a car I bought. Apparently someone decided to add some sand to the tank. Good luck and keep us posted.
Last edited by Jud Chapin; Apr 26, 2022 at 11:02 AM.
Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 1
From: South Florida
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
Hi all,
Really stumped with an issue and I've done all the research getting nowhere. By way of background, bought an 87 that was non running and sat for a very long time. Drained the very old gas, put in a new pump/assembly and found out the engine had a knock. Replaced with an 88 and have been driving it. I was having a brake issue and just fixed when this new issue pops up.
Start the car and it takes a couple of cranks but starts fine. Around 30 psi. Drive it and for the first 20 to 30 seconds its fine. Then it will start to bog down. Giving it gas has no effect and it'll putter and back fire then eventually get to speed but if you give it more gas it'll bog down again. Psi drops to 20 at idle when warm. When driving, psi will drop as low as 10 on acceleration. Replaced the pump, pressure regulator, egr, filter with zero results. Upon taking out the old filter, there was a TON of gunk in there and the filter maybe has 100 miles on it. At this point I'm completely lost on what it could be. Car had zero issues before this and its completely spontaneous.
Really stumped with an issue and I've done all the research getting nowhere. By way of background, bought an 87 that was non running and sat for a very long time. Drained the very old gas, put in a new pump/assembly and found out the engine had a knock. Replaced with an 88 and have been driving it. I was having a brake issue and just fixed when this new issue pops up.
Start the car and it takes a couple of cranks but starts fine. Around 30 psi. Drive it and for the first 20 to 30 seconds its fine. Then it will start to bog down. Giving it gas has no effect and it'll putter and back fire then eventually get to speed but if you give it more gas it'll bog down again. Psi drops to 20 at idle when warm. When driving, psi will drop as low as 10 on acceleration. Replaced the pump, pressure regulator, egr, filter with zero results. Upon taking out the old filter, there was a TON of gunk in there and the filter maybe has 100 miles on it. At this point I'm completely lost on what it could be. Car had zero issues before this and its completely spontaneous.
Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 1
From: South Florida
Haven't had a chance to work on it yet. I have ordered a new sock, yet another pump and a TPS and plan to see if I disconnect the MAF creates a difference. I understand that the filter being clogged isn't good but if that was the culprit I'd have to assume I would have at least gotten a few minutes of run time before it clogged again.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Haven't had a chance to work on it yet. I have ordered a new sock, yet another pump and a TPS and plan to see if I disconnect the MAF creates a difference. I understand that the filter being clogged isn't good but if that was the culprit I'd have to assume I would have at least gotten a few minutes of run time before it clogged again.
Psi drops to 20 at idle when warm. When driving, psi will drop as low as 10 on acceleration. Replaced the pump, pressure regulator, egr, filter with zero results. Upon taking out the old filter, there was a TON of gunk in there and the filter maybe has 100 miles on it.
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Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 1
From: South Florida
Yes I checked. The 20 psi is with the new pump, pressure regulator and filter all changed out. Same for the drop to 10 psi when driving with all the new parts.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
O.K. That's what I thought, but wasn't sure, the way it was worded.
SO...you don't need a TPS or a MAF. What you need to do, is diagnose why you're only getting 10-20 PSI, b/c that is insufficient and will cause bogging and backfiring through the intake.
How is the hose that connects the fuel pump outlet to the ending unit pipe?
SO...you don't need a TPS or a MAF. What you need to do, is diagnose why you're only getting 10-20 PSI, b/c that is insufficient and will cause bogging and backfiring through the intake.
How is the hose that connects the fuel pump outlet to the ending unit pipe?
Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 1
From: South Florida
O.K. That's what I thought, but wasn't sure, the way it was worded.
SO...you don't need a TPS or a MAF. What you need to do, is diagnose why you're only getting 10-20 PSI, b/c that is insufficient and will cause bogging and backfiring through the intake.
How is the hose that connects the fuel pump outlet to the ending unit pipe?
SO...you don't need a TPS or a MAF. What you need to do, is diagnose why you're only getting 10-20 PSI, b/c that is insufficient and will cause bogging and backfiring through the intake.
How is the hose that connects the fuel pump outlet to the ending unit pipe?
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
You might try running a clear siphoning hose to the BOTTOM of the gas tank and drawing out some fuel to look at. That should show if the tank contains any dirt.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Can you test to determine if it's the filter, sock, pump connection....or keep buying parts, I guess....(?)
Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 1
From: South Florida
Wouldn't have any idea how to isolate that. The only thing that isn't new is the sock, which is only a year old. Everything has been changed with no effect.
Racer
Joined: Jun 2006
Posts: 384
Likes: 62
From: Chicago Illinois
I was going to check when installing the new pump, now 3rd pump in under a year. The sending unit is new. I grabbed an autozone pump to do the last swap but now went gm genuine hoping that would help. Pump doesn't arrive until tomorrow so I haven't taken it apart yet. I didn't notice anything odd when i changed the pump last week though.
You need to blow out the lines both ways and confirm even flow. I don't think a faulty FPR would cause a restiction in flow. Rather, it would have no or really low pressure due to a leaking diaphram.
Try those things first and post back.
Ted
Thread Starter
Intermediate
Joined: Jul 2018
Posts: 40
Likes: 1
From: South Florida
Sorry to say, but something is seriously restricting your fuel flow and burning out your pump. 3 pumps in one year is ridiculous. You should have around 40 lbs when you hit the key and the system pressurizes and then low to mid 30s when running. Either you have a huge blockage in the lines, the filter is installed going the wrong direction or you are installing the wrong size pumps.
You need to blow out the lines both ways and confirm even flow. I don't think a faulty FPR would cause a restiction in flow. Rather, it would have no or really low pressure due to a leaking diaphram.
Try those things first and post back.
Ted
You need to blow out the lines both ways and confirm even flow. I don't think a faulty FPR would cause a restiction in flow. Rather, it would have no or really low pressure due to a leaking diaphram.
Try those things first and post back.
Ted
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
You could also devise a "T", install it starting at the rear, then move forward until you find a pressure drop. There are two ways to test...
Racer
Joined: Jun 2006
Posts: 384
Likes: 62
From: Chicago Illinois
It goes down to around 10 psi when driving and holds zero pressure when off, making me think it was the diaphram but changing it out had no change. Im not sure its the pump, just a guess. Filter is on correctly and gas was pouring out steadily when i changed the filter.
Good luck.
Ted
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Maybe. Hard to tell the way things are typed out, but he never mentioned a burned out or proven failed pump(s).
That would actually increase his fuel pressure; it'd run super rich.
The idea of blowing air through the lines is a great one....easy, fast....conclusive.
That would actually increase his fuel pressure; it'd run super rich.
The idea of blowing air through the lines is a great one....easy, fast....conclusive.
