Hello all! First time poster here. I have a 1985 240 Wagon and it has a strange problem. I purchased the car like this so I don't know any of it's history. The car idles well, but as soon as you hit the gas, it surges badly. I checked fuel pressure which is 62 PSI, going up to about 70 when the throttle is opened. I found a spec of 43 PSI, so I replaced the fuel pressure regulator, but it did not fix it. No change in fuel pressure reading either, still at 62 PSI. Any ideas??

 

You measured the fuel pressure at the fuel rail on the engine, opening the connector on the skinny bent pipe that feeds it?

Could the return line to the tank be plugged?

Dunno, but maybe disconnect the fuel return line back at the gas tank, stick it in a container, and power the fuel pump to see if there's a strong flow on the return line ?

 

Just to check your work, when you did the pressure test it should be 43psi above the manifold pressure. If the manifold pressure is 19psi (absolute pressure), then your readings are correct and your problem is not pressure. When you open the throttle, the manifold pressure increases, so does the fuel pressure. The fuel pressure regulator's job it to maintain 43psi (or what ever the spec is) above the manifold pressure. So to do the test right, you need two pressure gauges. If this is all old news to you and you check it like that, then I would say that there is a blockage or something or a hole it the diaphragm of the FPR. It's unlikely that a new one would be defective and in the same way, but you never know.

 

manifold vacuum at idle is like -8psi give or take, so that would nominally drop the fuel pressure reading to something like 35psi above ATM. WFO (sans turbo), manifold pressure rises to 0psi (relative to atmospheric) so per what titanjoe says, the fuel pressure should rise to 43psi.


a manifold pressure of 19psi absolute would only happen under high turbo boost, since standard atmospheric pressure at sea level is about 14psi. pressure gauges are almost always relative to atmospheric pressure (unless they have another reference), so if the pressure gauge reads 43, thats 43+14 absolute.

 

Thank you for the replies. Yes, I did check the pressure at the fuel rail where the feed line comes in. I did not factor in manifold pressure, so as you say the fuel pressure may indeed be correct. I agree also that a new regulator would not likely be bad in exactly the same way as the old one.

Any other ideas why it is surging so bad? I also put on a used throttle position switch and that also yielded no change.

 

put a jumper wire on the left sides of fuses 4 and 6 with the car off and listen for both the intank and main pumps, and if they sound "stressed". It could also be a dirty/defective air mass meter, the are fairly cheap from salvage yards.

 

When you say "surges", does that mean it tries to stall or take off? Does the car drive? Have you cleaned the throttle body flapper, actually taken it off and cleaned it real good with carb cleaner? Also, have you checked the plastic air duct that connects to the throttle body from the MAF for cracks and holes? My B230F developed a big hole in it that caused idle/running issues.

 

No it does not drive. As soon as you crack the throttle open it attempts to rev and then the rpm drops and it cycles up and down. The car has a new appearing Bosch Reman mass air flow meter. It does not have the flapper box style air flow meter.

 

I'd start here http://www.vcoa.org/700-900-faq/Fuel...sure_Regulator and work your way down. you have the LH2.2 system, so no OBD, so ignore those bits, but the rest is basically accurate accounting for the slight changes between the 240 and 700/900 (no 'radio suppression relay'...).

according to that, 60+ lbs measured fuel pressure at idle is way too high. that brings me back to the fuel return line being kinked or clogged. disconnect it from the regulator and see if you can pump some low pressure air into it.

 

Unplug the MAF and see if things change.

 

I dont think you main pump is working, I had a time when I could idle but as soon as I put it in gear to take off it died. Ended up being the connection to the main fuel pump was bad and was working intermittently.

 

with 62PSI fuel pressure?

 

I disconnected the MAF and it would hardly run. I tried to rev it and it surged. I also checked the hose which connect the MAF to the throttle body to see if there were holes at the bottom of it, and it all looked good.

 

if your fuel pressure really is 62 PSI, I bet your sparkplugs are soaked after one of these test runs.

again, I'd go here, Fuel System: Pumps, Relays and go through those tests one by one, sort out each thing before you move on.

 

I finally had some time for some reading. Pierce, yeah I didn't think of the gauge starting at 14psi as 0 anyway. So I was off there by a good bit.

Overpressure is a weird thing, but here's another idea:
All this would make me think that something is preventing the new and old FPR from regulating properly. Since I can't see the car I'll ask some questions that may seem too obvious.

The FPR connects to the intake manifold by a little vacuum tube. Is that tube connected? Is it not cracked, old and leaking? Is it not plugged? Is it the right part number?

Everything seems to to work fine, but the system that regulates fuel pressure. A blockage could be a problem like Pierce suggested a while back. Look for the return line to be pinched. You said that you purchased the car like this so maybe a guy was working on the gas lines and clamped some of them shut the pull some things apart.

 

open vacuum line on the regulator would make it think you are wide open.

the gas lines are in the trunk behind the back seat. goes from the tank pump to the filter, through the main pump, to the engine rail to the pressure regulator, and back to the tank.

on this diagram, I think #1 and #4 are the return line/pipe

 

Well I dug a little deeper today. It looks like the cam timing is off. I lined up the cam pulley mark with the little bulge in the rear plastic cover, the distributor is on number 1, but when I look at the marks on the crank pulley, it's about 1 inch to the right of the graduated timing marks. I think I will try to install a new belt next weekend and see what happens