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89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

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89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

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Old 09-01-2015, 08:24 PM
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89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

Good evening all. Our 89 2.8l has been running pretty well for the last 3 months and my daughter is having a ball driving it. Well, in the last couple of weeks the car will start and run well but sometimes (becoming more frequent) the engine gets to operating temp and begins to lose power until it becomes completely gutless. It is difficult keeping it at 50mph in this condition.


So this evening, I get it in the garage and pull the FPR line and I think there is a faint (very) smell of gas in the line but really think it is more my imagination. So I figure, let me hook up the fuel pressure gauge and see where things are. Key on the fuel pump, 40lbs, start the car 37lbs. Turn the engine off, pressure drops to 0 immediately.


We put a new ACDelco pump in 3 months ago, set of SouthBay injectors, new cat, tune up and various sensors, FWIW. Fuel pressure held for 2 hours with only 2-4lb drop when we did the repairs. Any ideas guys? Why would pressure drop immediately?


I will keep searching but not having any luck.


Thanks

Last edited by Fluf97zj; 09-02-2015 at 05:14 AM. Reason: Add more detail for work done recently
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Old 09-02-2015, 09:03 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

The fuel pressure regulator could be bad and leaking. Try removing the vacuum hose to the regulator and see if you see or smell gas.
One or more fuel injectors could be leaking.
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Old 09-03-2015, 12:43 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

Thanks Mark
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Old 09-03-2015, 07:59 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

was that one of the years that had the leaky cold start injector [ 7th injector ]
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Old 09-03-2015, 08:23 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

I had his issue befor and it turned out to be my fuel pumps check valve . Although it can be caused by a few things
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Old 09-03-2015, 08:30 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

What type of line did you put between the pump & the metal line? This is often a source of fuel pressure loss. Had the factory rubber hose on my 88 do this with near identical results. Most hose supplied with generic replacement pumps is of questionable quality.
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Old 09-04-2015, 04:31 AM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

Actually, I reused the factory isolator and did not use the included hose on the ACDelco pump. Figured I should put it back as original and the instructions denote the hose was for different years than '89 if I recall correctly. After thinking about it, I guess the hose would have worked fine. Did not even think about that as a cause of the pressure drop so THANKS guys.


I am going to have to drop the tank again anyway because the sender is bad now so I can change the isolator out for a section of FI hose and clamps then.


However, could this cause the poor engine performance as it gets to operating temp? I should have originally posted that when I replaced the pump in May, the pressures held as per spec. If the fuel pressure regulator is bad, would one symptom be that it allows the fuel to bleed off to the tank immediately? I am really not sure I completely get the operation of the FPR.


I did find some info on TGO about clamping the rubber fuel lines to determine which side of the system is the problem. I am going to try that tonite.


Thanks guys and keep the ideas coming. This is a huge help as my daughter is anxious to get this fixed (and she is learning a lot along the way). I will post what we find with our test.
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Old 09-04-2015, 06:36 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

Originally Posted by Fluf97zj View Post
Actually, I reused the factory isolator and did not use the included hose on the ACDelco pump. Figured I should put it back as original and the instructions denote the hose was for different years than '89 if I recall correctly. After thinking about it, I guess the hose would have worked fine. Did not even think about that as a cause of the pressure drop so THANKS guys.


I am going to have to drop the tank again anyway because the sender is bad now so I can change the isolator out for a section of FI hose and clamps then.


However, could this cause the poor engine performance as it gets to operating temp? I should have originally posted that when I replaced the pump in May, the pressures held as per spec. If the fuel pressure regulator is bad, would one symptom be that it allows the fuel to bleed off to the tank immediately? I am really not sure I completely get the operation of the FPR.


I did find some info on TGO about clamping the rubber fuel lines to determine which side of the system is the problem. I am going to try that tonite.


Thanks guys and keep the ideas coming. This is a huge help as my daughter is anxious to get this fixed (and she is learning a lot along the way). I will post what we find with our test.
clamp off the return line , and turn the key on and off and see if fuel presure belleds down .

if it does its either a leaking injector , or the check valve back at the pump .
if u suspect the injectors remove the upper intake and pull the fuel rail injectors out and turn the key on till it builds presure then shut it off and look at the injectors to see if any are leaking


normally running good when col , and getting progressively worse as it gets hotter is usually the ignition control module , and ive also seen cat converters that would clog up as they heated up as well causing poor performance


also look into the coolant temp sensor located on the driver side front of the intake manifold , this can be double checked by reading the resistance across the 2 pins and then cross refrencing it with a chart to tell u what resistance u should see at what temp . do not probe the wires that plug into the sensor , if u leave them hooked up the value of the reading will be cut exactly in half.

so unplug the connector and test dirrectly to the pins of the cts
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Old 09-04-2015, 08:56 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

Hey Fluf97zj if you find that it is a leaky injector send them on in to us and we'll clean them for you. Let us know
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Old 09-04-2015, 08:57 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

If you find that you have a leaky injector let us know and we'll take care of it for you.


Oops... sorry for the duplicate post!

Last edited by southbay08; 09-04-2015 at 09:03 PM.
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Old 09-05-2015, 12:18 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

Originally Posted by southbay08 View Post
If you find that you have a leaky injector let us know and we'll take care of it for you.


Oops... sorry for the duplicate post!
Thanks for the follow-up!
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Old 09-06-2015, 06:17 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

Ok, first, thanks to everyone who gave us some pointers. We tore the plenum off the engine and checked the injectors for leaks and saw none leaking. So then we went into the FPR and there we found a big chunk of trash not allowing the FPR to seal up Replaced the FPR and the system seems to want to hold pressure . We will finish up with the rest of the job tomorrow and I will let you know if the ICM and coil fixes the gutless drivability when at operating temps.


Thanks again all.
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Old 09-07-2015, 12:00 PM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

UPDATE: We put the engine back together and the car runs almost perfectly. Idle is smooth starts right up, idle settles right down and once it is up to operating temp, runs great.

We replaced the fuel pressure regulator, the ICM and ignition coil. We battled a vacuum leak that was a part of the old plenum gasket we missed when we did the injectors. We changed out the thermostat while we had the engine apart and now the temps are less erratic. Idles smooth as silk and I am so much more confident with my daughter driving it.

Thanks again to everyone for your help.
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Old 03-06-2016, 09:16 AM
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Re: 89 2.8l Camaro Fuel Pressure drops immediately upon shutoff

Similar situation guys... I have 87 TPI 305 that I just replaced original engine with new 305 crate. After everything was connected, would drive fine, but stall out within seconds of coming to a halt (say at a red light) unless I kept the RPMs up. FP holds fine while running, but drops off when engine is turned off. But to bypass for the time being, I pulled the line off the FPR to the Plenum and plugged it. Runs fine for the most part, but if engine heats up, it starts to surge/fall a bit and the Chk Eng Lite comes on (but goes back off shortly after back driving). The FPR and EGR valves are all new. Have not changed out fuel pump as for the hassle at this point... and the car is using more fuel than usual obviously with the regulator not connected (open) to anything. Suggestions where to go / what to try next?
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