Fuel Pump System Question '93 TBI

Fuel Pump System Question '93 TBI

Postby Cooper24 [OP] » October 16th 2008, 3:53am

I have a question about how the fuel pump system works. Here is what I understand so far. When you turn the key, the relay sends power to the fuel pump for a certain amount of time and shuts off. When the engine starts, the fuel pressure rises and then turns power on to the fuel pump. The fuel pump sends gas to the TBI. The fuel pressure regulator maintains fuel pressure and when it goes over, gas is sent back to the gas tank. Here are a few questions I have:

Does the fuel pump run constantly while the vehicle is running, or does it cycle on and off?

If it does cycle on and off, what controls the fuel pump?

Can I put a jumper on the relay (bypassing the oil pressure power) to see if sending constant power to the pump solves the problem?

The reason I am asking is because I am having a problem with the van kicking and sputtering like crazy. I have replaced almost every sensor of the ECM system. I have even replaced the fuel pump. With no change at all. I took it in to a shop to troubleshoot the problem. They said the ECM system is working fine and reading all the sensors correctly. They did a dead head pressure before the fuel filter and said the pressure was varying between 14 and 22 pounds and it was erratic. He advanced the timing to help the system deal with the lean mixture.

It is a new fuel pump and it acted the same way as the old pump. I do understand that new fuel pumps are not always reliable. This issue with the van actually started after a mechanic changed out the transmission (long story). This is why it is hard for me to believe it is the pump. Anyway, I also realize that two failures can happen at the same time and they may be unrelated.

One thing is that I am convinced the issue is fuel pressure related. When it kicks and sputters, it acts the same way as if I let the gas tank get empty and it cuts out when you go around corners. I just can pin down the location of the erratic behavior. Hoping that understanding how the fuel pump system works will help find the problem.
'93 Astro EXT 250k
'93 BMW 525 235k
'79 Porsche 928 75k
'77 Fiat Spider 100k
'00 Ford F250 V10 124k
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Re: Fuel Pump System Question '93 TBI

Postby Gary » October 16th 2008, 5:31am

Change the fuel pump wire harness that is inside the tank.Might want to put on a new strainer while you in there.
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Re: Fuel Pump System Question '93 TBI

Postby gtkane » October 18th 2008, 5:35am

Let's start with"someone changed the transmission"...
Get under the van and check the fuel lines that run beside the trans on the drivers side. Do they look pinched or twisted?
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Re: Fuel Pump System Question '93 TBI

Postby Gary » October 18th 2008, 8:20am

gtkane wrote:Let's start with"someone changed the transmission"...
Get under the van and check the fuel lines that run beside the trans on the drivers side. Do they look pinched or twisted?


:confused: :confused: :confused:??? As I understood it,this developed after the tranny was replaced and drove fine for awhile.Right???.
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Re: Fuel Pump System Question '93 TBI

Postby Cooper24 [OP] » October 20th 2008, 4:31am

No, the problem was noticed immediately after. I've checked all the fuel lines, electrical harness as best I could from underneath and with the doghouse off and haven't found anything wrong visually. Its driveable but totally sucks. I'm short on cash and need the vehicle daily so I live with the issue. This is not a "slight" problem.
'93 Astro EXT 250k
'93 BMW 525 235k
'79 Porsche 928 75k
'77 Fiat Spider 100k
'00 Ford F250 V10 124k
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Re: Fuel Pump System Question '93 TBI

Postby Gary » October 20th 2008, 8:26am

Do you still have off the dog house??.With it off,run it after dark and see if you see sparks off the plug wires.Try it and let us know what you see.
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Re: Fuel Pump System Question '93 TBI

Postby Cooper24 [OP] » November 10th 2008, 4:12am

Very long post.

OK, finally got some time to pull it off. Didn't need to wait until dark to see the large lightning bolt going from the coil to the top of the plug. Seems like it was loose so I got that fixed. After dark I ran the engine and there was a very nice light show. I could see the plug wires glowing as well as the coil. I'm assuming I wouldn't see this with a good pair of plug wires. Anyway, no sparking anywhere.

I decided to try hooking up a spare temp sensor and leave it dangling so it would not get hot. I understand that the computer will run on presets until the engine temp gets to about 97 degrees or something. This seemed to get me through last winter although it chugged a little more gas. Last summer I took it to a mechanic to verify the computer system was working and let me know what was going on. It was starting to run really bad since the outside temp was warm. He rehooked up the temp sensor and advanced the timing to get it to run. He told me he thought it was the fuel pump which didn't make much sense. Anyway, I could not get the van to run tonight like it ran before with the system bypassed.

Is there another way to bypass the computer?

Some other observations - I checked to see how the injectors were working using a mirror. At idle it seemed like a fine spray on the throttle plates. I reved it up, but really couldn't tell much. It normally revs up just fine with no hesitation. It just bombs when you just barely touch the gas under load.

I messed with the timing a little bit and it seemed like the distributor shaft was a little loose. I could move it back and forth a small amount. I'm not sure if this is normal. I tried locking it down at different spots and it didn't seem to matter.

***One thing that seemed strange is that my injectors were very quiet. In the past they have been very noisy with the doghouse off and the air cleaner off. I didn't notice any sound this time. Could this be a problem??

ran fuel pump with a direct wire from the battery to the test port. no change.

Here are some typical symptoms (with temp sensor plugged in and timing adavanced):
van drives marginally better as gas tank gets empty, runs like crap after taking off the gas cap and filling up

runs better if I wait for the engine to warm up to at least 160 before driving, than if I start it and take off (runs like crap)

driving at 70 mph - if I try to keep van at 70 by depressing pedal a little bit, it stutters and kicks, if I downshift to lower gear with really high rpms, it takes off...if then I let off the pedal, let it shift and then give it a little gas, it sputters like crazy

Starts up hot or cold on first few cranks like it always has.

ran pretty good this summer with outside temp high, runs really bad now that it is really cold out.

(BTW - I changed all these out last year: temp sensor, EGR, PCV, MAF, ICM, throttle position sensor, oxygon sensor, fuel pump)

Check engine light comes on and goes out during driving...checked codes and they are lean mixture (from 02 sensor) and another one for the computer not sensing voltage from fuel pump for more than 2 seconds after it told it to turn on. I believe this would lead someone to believe this was the fuel pump but then bypassing the computer and having it run OK wouldn't lead me to believe it was the pump.

Sorry so long. Any help or suggestions appreciated now matter how off the wall they may be. This problem is killing me!
'93 Astro EXT 250k
'93 BMW 525 235k
'79 Porsche 928 75k
'77 Fiat Spider 100k
'00 Ford F250 V10 124k
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Cooper24
Fueling (Empty tank)
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Re: Fuel Pump System Question '93 TBI

Postby Cooper24 [OP] » November 14th 2008, 4:28am

Gary,

Thanks for the tip. I bought a new coil, cap and wires. Problem sovled! This has been plaguing me for a year and a half...AHHHHHHHHHHHHHHHHHHHH. You know I had replaced every other component in the system EXCEPT the $20 coil. I'm kicking the crap out of myself right now.

Oh well, wife is ticked...she wanted to push it off a cliff somewhere and get something else!
'93 Astro EXT 250k
'93 BMW 525 235k
'79 Porsche 928 75k
'77 Fiat Spider 100k
'00 Ford F250 V10 124k
Original Poster [OP]
User avatar
Cooper24
Fueling (Empty tank)
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Posts: 7
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