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  #1  
Old 08-22-2007, 01:25 AM
tmjvln5 tmjvln5 is offline
 
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Bang Head surge problem

Hi i bought a TR a little over a year ago and it has had a surging problem since i first got it. It occurs when i accelerate hard at around 10-15psi but if i accelerate slowly to 15+ psi it seems pretty smooth. Some of the things ive replaced that i thought might be related are

egr
pcv
air filter
oxygen sensor
mass airflow
fuel filter
cracked exhaust manifold

the car seems pretty stock its a 87 turbo t, thanks!
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  #2  
Old 08-22-2007, 02:36 AM
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Question Re: surge problem

By 'surging', do you mean the whole car is accelerating erratically?

Are you getting any knock (on a scan tool) while this happens? Does the boost fluctuate? Does the fuel pressure fluctuate?
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Old 08-22-2007, 04:14 PM
tmjvln5 tmjvln5 is offline
 
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Default Re: surge problem

sorry surge was a poor choice of words. its like the acceleration is pulsing as if i was pumping the gas pedal. the boost does fluctuate by 1 or 2 psi while this is happening and the longer you hold the gas pedal down the worse it gets. Im afraid to hold it down too long because after a while the boost gauge flucuates wildly and the engine repeatedly makes a popping or clunking noise. Theres a fuel pressure gauge under the hood and the idle pressure ive tried running between 25 and 35psi. ill have to hook one up inside to check while im driving. Im not sure what you mean by knock on a scan tool. sorry im still a bit of a greenhorn.
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Old 08-22-2007, 04:47 PM
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Exclamation Re: surge problem

Can I assume that the fuel pressure is always checked with the vacuum to the regulator connected?

Do you have any sort of scan tool to determine what is going on with the ECM while the car is running? (i.e. OTC, AutoXRay, TurboLink, DirectScan, PowerLogger, etc.)

Sounds like there may be a genuine issue. Your fuel pressure may be a bit low. Discounting the likely vacuum, it should be in the mid-to-high 30's (vacuum on) which would equate to low 40's vacuum off. Not enough fuel pressure, and the car will run lean. If it runs lean, it will knock (detonate) which could lead to head gasket failure or worse. There may already be some sort of combustion chamber leak causing the symptoms you are seeing.
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Old 08-22-2007, 11:03 PM
tmjvln5 tmjvln5 is offline
 
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Default Re: surge problem

I bumped up the pressure and tried the 35 to 40 range with the vacuum on but i get the same performance. maybe it is a compression leak. The guy who sold it to me claims its got 50-60 thousand miles on a total rebuild where the engine was bored out but he might be full of it and thats plenty of time to blow it again. I ran the codes with a GM actron code reader and only got a 12 which is apparently a normal code saying the ecm is functioning. The code reader isnt the same thing as the logger you are talking about though is it?

Last edited by tmjvln5; 08-22-2007 at 11:13 PM.
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Old 08-23-2007, 02:17 AM
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Thumbs down Re: surge problem

Quote:
Originally Posted by tmjvln5
The code reader isnt the same thing as the logger you are talking about though is it?
No. The "code reader" is electrically equivalent to a paper clip. The logging/scanning device is a somewhat intelligent tool that can read data from the ECM.
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Old 09-03-2007, 05:14 PM
tmjvln5 tmjvln5 is offline
 
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Default Re: surge problem

Hey sorry i havent replied in a while. I've been back at college and havent been able to work on the car till now. I just did a road test with a gauge taped to the hood and got some interesting results. The idle pressure was at about 36 37 psi with the vacuum hookup and 42 or so with it off. When I drove it and got the turbo up to 10-15 psi the fuel pressure did not exceed 40 psi. With a boost of 10-15 psi and a base of 42 without the vacuum hookup its my understanding that the fuel pressure should be 52-57 psi. Any ideas what might cause this? Im thinking a tired fuel pump or a faulty regulator?
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Old 09-03-2007, 08:04 PM
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Lightbulb Re: surge problem

Quote:
Originally Posted by tmjvln5
Im thinking a tired fuel pump or a faulty regulator?
Excellent analysis. Presumably you have a good pressure/vacuum source to the regulator.

You could replace both. (That is a little priey...) Or you could try to determine which is the real culprit. Its a little tough to get pressure to the regulator, but it can be done. You can do it even at idle. And should be able to see if the pump can keep up. This isn't 100% a road test, but its better than nothing. You could use an air hose/air tank or supply, some clever fittings, and your fuel pressure gauge to see what you get.

Another method is just turn the pressure up to ~60 PSI and see if it stays there during boost. It may...it may not.
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Old 09-15-2007, 04:43 PM
tmjvln5 tmjvln5 is offline
 
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Default Re: surge problem

The next chance i had i tried running the car at ~60psi at idle and then drove it. As soon as the turbo kicked in (0+ psi) the pressure reading from the fuel pressure guage dropped proportional to the turbo boost. Im not exactly sure what this means. I would guess that maybe the regulator is just broken or it isnt a boost compensating regulator. It looks like its been fitted with an aftermarket regulator but i cant find a part number on it? Any ideas?
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Old 09-15-2007, 06:10 PM
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Lightbulb Re: surge problem

If it has a nipple on it in addition to the fuel inlet/outlet fittings, there is a good chance it is set up for boost pressure compensation.

If the pressure goes down as you accelerate, (which it is) it could be either the pump or regulator. Though it could be either the regulator, or the line(s) to the regulator being faulty. Clearly you can manually adjust it.

Is there any way you can apply external pressure to the regulator while the car is at idle and read the fuel pressure? That would assure that an internal leak is not the issue.

Can the regulator be disassembled? Dirt may have lodged in it and may be causing problems.

If you can eliminate the regulator, then it all will point to the pump.
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Last edited by Keller; 09-15-2007 at 06:13 PM.
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