ok so my 91 tpi, started running like crap the other day on the highway, when i would step down on it it would rev up real slow, and did not have any power. So i came home and did a fuel pressure test on it, taped they gauge to the windshield, and took it back out on the highway, when i turned the key on it went up to 36psi , whet started and idleing it droped to 28 psi, whenever i would push the pedal the furl pressure, would go up and down with the rpms, the range was 28-36 psi is that ok, why does the fuel press go up and down so much?

 

The pressure goes up with throttle opening because of varying vacuum at the pressure regulator. This is normal. However, your pressure is low. Normal key on engine off pressure would be 40-47 psi and should hold for at least 30 seconds. Engine idling pressure should be about 35-37 psi. You may have a bad regulator. Try pinching the return line off in the rubber section and see if pressure spikes to about 80-100 psi. If so you most likely need a regulator. A weak pump could cause this but that would be unusual. A bad pump would more likely cause pressure to be low under load or at higher speeds.

 

ok i went out today and unhooked the vac line to the regulator and my psi jumped from 28 to 38 psi hooked it back up and it dropped back to 28 , then i kinked the return line and it was bouncing in between 80 and 90 psi , so is my regulator messed up then , it didnt have any gas coming out of the vacuum port when i unhooked it. and i forgot to mention the fuel pump was replaced like 6 years ago but it has less than 2000 miles on it since i replaced the pump , didnt get drove for several years

 

pinching your return line takes the place of the regulator. from the information youve stated, i would try a new regulator or an afpr.

 

well got the presuure regulator in now i got good fuel psi 42 at idle up to 50 when i rev it, but it still falls on its face when step on it on the highway, could the timing be off by a little and make it do this? i have i mechanic set it for me when he had the tech hooked up to it but i noticed the dizzy is not very tight

 

it sounds like you might need to some how monitor the fuel pressure while you drive. this topic has been discussed before, keep searching to find related posts.

you will have to rule out different possibilitys like a clogged fuel filter. there cheap so just replace it.

i looked at all possibilitys because i thought my fuel pump would be good past 10,000kms... wrong! what a piece of junk. i just installed a new walbro 255 and it runs great.

btw your pump may hold pressure but not produce volume.

 

Like T/Atime says, monitor fuel pressure while driving to be sure there is no drop off under heavy load. This would be caused by a weak pump or restriction in the line or filter. You can watch fuel pressure by connecting a pressure gauge with a long hose and taping it to the windshield. Timing could cause the engine to fall on its face on throttle tip in. So can old ignition wires or a faulty ignition coil. To test for this you need to connect an inline spark tester, first at the plug end of more than one ignition wire and watch for spark drop out as the engine falls off. Then work your way back to the cap and of the wires and finally between the coil and the cap.

 

well looks like i got my weekend planned lol! ill put the psi gauge back on the winshield tom. and check the fuel filter , it was just replaced a month ago , then ill work my way throught the timing and plug wires, and coil lol, at least it has new plugs in it

 

You got the right idea. I also had this problem with mine falling on it's face so I put a gauge on my windshield and all was fine there. Turns out fuel level was just low. I've got the digital dash and it's readings aren't worth squat.

Either way, best of luck! Are you getting a check engine light at all?

 

i thought of that to and went and but 5 more gallons in the car the other day , i couldnt get a lucky break like that lol,.
it doesnt pop a ses light or have any codes

 

psi while driving check out ok, checked the timing , it was ok, looked at the plug wires they looked ok , i replaced them like 5 monthes ago with the plugs, so now what buy me a new coil? could the tps be a problem here , what ever it is is getting worse now it doesnt want to go past 3000 rpms

 

I hate to even suggest this but sounds alot like a restricted catalytic converter. Maybe you don't have to worry about emissions in your location. If that's the case then you can just drop out the cat and replace it with straight pipe. Otherwise, you'll likely be buying a new cat. To verify that this is the problem, the easiest way I know is to remove the O2 sensor and go for a short drive, looking for an improvement. You will get a check engine light but it will go away after you reconnect the sensor. Other way is to drop the exhaust at one manifold and separate the joint enough to allow decent flow. Be careful not to break a stud. Lube them up good with Liquid Wrench or equivilent.

 

thats kind of what i was thinking id do next it sounds like there is presure coming out the air tube on the cat where the moffler shop guy didnt get it connected right, if i do away with the cat and straight pipe it what do i do with the air tube?

 

well turns out the cat was the culprit , and for all you ozone lovers,lol, yes i did put a new cat on it, thankx for the help ase doc