1985 745t

So, after reading numerous resources on the web I believe my Fuel Pressure Regulator is bad or I may have small leaks (that I can't see) on the intake manifold (at the hosing connections). Does anyone know if you can remove and repair the regulator? What's the best way to test for leaks at the hoe connections on the intake manifold?

Read on if you are interested in some background and data on this, it may prove interesting to other people who notice performance drops at high boost but whose vehicles run fine in normal circumstances.

BACKGROUND:

I recently replaced my sender/primary pump. After taking the car out it seemed to lose power slightly when flooring the accelerator and fully engaging the turbocharger. It felt like it wasn't getting enough gas, or something was holding it back slightly.

ANALYSIS:

I first thought I must have installed the sender assembly in a way that slightly interrupted the flow of fuel at the pre-pump nozle, or that the new hose design included with my new sender (they now use an accordian hose in place of the straight hose for the connection between the pre-pump and sender assembly, I imagine to reduce breakage of the hose with bending and age) was affecting fuel delivery to the main pump.

However, in researching the issue I came across numerous articles that discussed possible issues with the FPR on turbocharged vehicles. They discussed how the car can appear to be running optimally during idle and normal operations, but that "On acceleration under turbo boost, the car will lose power and may have black smoke coming out of the tailpipe." This seemed familiar, so I read on. Seems visually imperceptible intake air leaks under pressure between the turbo outlet and the engine can cause this to happen. Also, a fuel pressure regulator that sticks shut with pressure on the vacuum line from the intake manifold, increasing the pressure to the injectors to full pump pressure, which is near 100 psi, may cause it.

SOLUTION:

Haven't actually done the work yet, but I plan to test all connections on the intake manifold for small leaks. Additionally, I will probably just replace the FPR while I'm at it. I thought about installing a pressure gauge to actually see if it is malfunctioning, but since the FPR costs around $35 and the gauge sells for $20-$40 I figured I might as just replace it and not waste the same money testing it.

If you have any thoughts please post them, I'd love to hear the opinions of more accomplished and knowledgable volvo owners.

-Rick

The FPR is easy to change: remove the vacuum hose, place a rag around the fuel connection, and loosen. Fuel will come out. Once it stops, remove and replace the FPR. To be fancy, pull the fuel pump fuse and run the engine until it stops, or use a vacuum pump on the FPR vacuum fitting and relieve pressure that way.

Steve:

Thanks for the message, can't believe someone FINALLY posted a response... ;)

I tried to pull the vacuum hose on the FPR to see if it is in fact broken (read how it might shoot fuel), but it was fixed pretty tight. I'll probably try and test it a little bit before I throw the new one on and see what happens.

BTW, I've been trying to figure out an acceleration issue over the last few days with another guy on this board and was wondering if you had an idea. I've included the description below. This problem is the reason I am replacing the FPR (cheap first step)... maybe a challenge for ya.

Thanks,

Rick

ACCELERATION WOES:

1985 745t

I recently replaced my in-tank pump and sender assembly. Everything seemed to go fine, but lately my acceleration has been odd.

When accelerating with the tach below 2750 acceleration is pretty poor. Then it takes off around 2800. When I floor it the car seems to start surging very slightly. The turbo engages and it does accelerate faster, but it comes in almost imperceptible waves. This problem was most noticeable going up a long hill when I put the petal on the floor. The turbo engaged, I passed other cars, but the acceleration just seemed to stop at about 80% of capacity and start to display long, almost imperceptible surges.

I have also noticed that initial acceleration (when engaging in first or reverse from a standing position) seems to require me to depress the gas pedal farther than I had to in the past. If I don't push it down farther it will start to stutter and rumble a bit (like it should when the clutch is out, its in gear, and there isn't enough gas). Not sure if this is related.

I also have the slightly vacillating tach (between about 750-825) in idle, but I had that beforeI put the new sender/in-tank pump in (was hoping it would disappear).

Finally, after drives as short as 15-20 miles I'll often look in at the exhaust manifold and see it glowing red-hot. Specifically, it seems like the square joint between the turbo assembly and the manifold glows.

I figure it's either a knock sensor problem or a fuel pump regulator problem, but am open to any and all recommendations.