240 No control pressure no matter what I do

Hi Fellow Brickers,

To start, I want to say I?ve been avoiding this. The issues between me and my 240 have been long standing and for years, I?ve told myself we can work it out on our own. But I?m at my wits end and I?m tired of spending nights either sobbing into a gas-soaked rag or banging my head against the valve cover in frustration. So I?ve adorned my tough skin and I?m ready to sift through the chaf and scrutiny of the interweb to get some help. Let the couple?s counseling begin!

The car is a 1983 240 turbo. In short, I have no control fuel pressure. I am constantly running at system pressure, about 76 psi for my car, which is causing the car to run really lean. Starting is very rough- car will fire up, immediately die for multiple times before it eventually finds an extremely weak idle and sputters for a while before it finally warms up. Driving is slow with a lot of hesitation and since I?m running lean, the combustion temp is extremely hot to the point where my turbo and exhaust manifold glow bright red at night and I?m afraid my valves are looking like burnt toast.

The problem is I?ve changed my control pressure regulator 3 times, one of which is a completely refurbished and costed more than most of you would spend on a low mileage 240, and still no control pressure. I have correct voltage from the CPR wire harness and resistance across the CPR. I?ve adjusted my idle control set screw thing in my distributor extensively. My FV is buzzing away happily and the duty cycle is in the correct range according to the Bentley manual. I?ve cleaned out my fuel distributor and made sure I have no blockages in any of my fuel lines. I?ve also tested my return line at my gas tank and have good flow there. When I attach a volt meter to my O2 sensor and drive the car, it reads between .3-.6 volts at idle but on acceleration will drop to below .3 and won?t increase, basically no enrichment (which is consistent with running really lean? I think). Interesting thing is when I unplug the O2 sensor, voltage reads at .5, doesn?t change no matter what I do, and the car backfires a ton and doesn?t drive down the road.

Other things I have replaced on the car include both fuel pumps, the wiring harness, fuel pump relay, and all necessary fuses.

I?m hoping one of you can help me out. Is there something that I?m missing? Should there be another test I could do? Anything short of driving this car off of a cliff and buying a Saab (just kidding). I?m new to the k-jet, and car mechanics for that matter, so any advice would be much appreciated.

Before we get too far along in check this, check that, I'd want to confirm your measurement technique. Especially that you say you get "no" control pressure and not "no reduction in control pressure."

http://cleanflametrap.com/kjetGauge.htm

While you're looking at Art's great pictures, check that your k-jet hoses are all routed to the correct locations. I don't know what would happen if some were swapped, or if it's even possible for the banjos to fit in a swapped position.

Yeah, you are right, I should have said I get no reduction in control pressure. I think I am testing the pressure right. I have a set up much like on your site. I tap in at the top of the distributor where the CPR line runs out. The banjo joint on the line to the CPR is connected on the other end of my gauge with a valve to open and close flow to the CPR. When closed, gauge reads 76psi. When opened, pressure drops for half a second as fuel runs through the CPR but will immediately increase back to 76psi and stays there.

And I've thought about lines going to the wrong areas (because I did take them all off to clean them) but I'm positive they are going back to the right positions (at least 95% sure...)

Well, you have me stumped. Something is blocking the return just as efficiently as the shutoff valve in your test rig. And I read that you already cleaned pipes and checked return flow.

Follow the return line from the CPR to the fuel distributor and post a pic of where it's connected.

It'll take me a few days to get to the garage to take a pic but its connected to the front side of the distributor, on the opposite side as the cold start injector line.

I was hoping you wouldn't say that Art ... Yeah, I ran carb cleaner and compressed air through all my lines and I disconnected the return line from the sending unit at the tank and had good flow there. I didn't measure the rate but it filled up the pyrex measuring cup I was using real fast.

The line for the control pressure fuel return should be connected near the fuel return line. If it isn't it's either clogged or on the wrong port. Probably the port for the cold start valve which would be system pressure.

^ This. The CS valve connection is on the front of the distributor.

Yeah, I should have said next to the return line. According to that diagram, I should have everything hooked up right. The only thing I can possibly think I did was switch lines going to and from the CPR but I dunno. I'll make sure I have that correct.

Thank you guys for all the help, I agree that its got to be something simple, its why it has been so frustrating for me. My one thought is that the distributor is plugged at the return port? Don't know how I would go about testing that.

And the thing I'm hung up on is the symptoms when the O2 sensor is unplugged. It should default my FV to 50% which will cause most cars to run rich, i think... With mine uplugged, I open the throttle, the car just sputters and backfires. At first I thought the O2 sensor was broken but it definitely is doing something because the car actually goes down the road when its plugged in, as opposed to not. And then there is the lack of enrichment with completely open throttle. Do I chalk both these up to high pressure as well?

The high control pressure makes for a lean engine all the time. Disconnectiong and going to 50% duty cycle or 45 degrees dwell is proper. It's a default value when the lambda controller can't read the sensor.

For acceleration enrichment there is an enrichment sensor on the firewall. At 2.9psi boost it enriches the mixture by grounding pin 7 of the lambda controller.

Get the control pressure sorted out first then move on to the boost enrichment sensor.

I thought about it a bit more and I think your CPR / WUR hoses are swapped. Inside the WUR is a thin metal disk with a spring pushing it closed against a center outlet tube. The inlet tube goes to the outer doughnut shaped region of the metal disk. When the inlet pressure, applied across the larger outer area of the disk, is greater than the spring force, the metal disk deforms enough to let fuel go out through the center tube.

If you reverse the connections, the inlet pressure only has the tiny center area to push on the disk, and the disk will stay closed.

To see better what I'm talking about, find the "Volvo K-jet Fuel Pressure Regulator (WUR) Servicing.pdf" at https://ozvolvo.org/archive/archive.php

O2 sensors only start to generate a voltage when they get up to exhaust temperature. Before this, they're at 0volts. The lambda system is setup to drive the frequency valve at a fixed 50% before the O2 sensor is warmed up (or when unplugged, which also causes 0volts). The mixture adjustment screw is used to run a slightly rich mixture before O2 is working. Original volvo specs were 1% CO on a gas analyzer, or roughly a 14.3 AFR if you have a wideband. Once the O2 sensor is up to temperature, it will automatically adjust the FV to get to 14.7 AFR.

I forget who on here told me this, but you can disconnect the O2 sensor and then with one hand holding the bulkhead sensor wire connector, alternately touch your other hand to the + and - posts on the battery to make the mixture go up and down. (The O2 sensor input is very high impedance, meaning it draws almost no power. Even though the human body is a poor conductor, it's still good enough to swing the O2 sensor input up and down.)

bobxyz said:

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I forget who on here told me this, but you can disconnect the O2 sensor and then with one hand holding the bulkhead sensor wire connector, alternately touch your other hand to the + and - posts on the battery to make the mixture go up and down. (The O2 sensor input is very high impedance, meaning it draws almost no power. Even though the human body is a poor conductor, it's still good enough to swing the O2 sensor input up and down.)

Click to expand...

Just to add, the lambda controller puts its own bias on the oxygen sensor connector resulting in that steady 0.5V that seems to be confusing. That's how the controller knows the sensor is not warm yet, weak, or defective. It is generated internally by a voltage divider with very high value resistors, so it is easy to overcome the 0.5V bias with a hand grasping the terminal and the other hand touching ground or battery + post. When you try this (if you try this) keep your high impedance digital voltmeter connected to see that it does.

The hose between the top of the fuel distributor and the 10mm rear connection at the WUR/CPR is the only hose with an 8mm banjo on one end and a 10mm on the other. If you are measuring system pressure between the two then the WUR fuel screen on is the problem. I know you said you have replaced the WUR three times and got the same result. But . . . maybe . . . just maybe . . . you have a third bad WUR.

My experience is that WUR's fail at system pressure.

Yeah, I agree that swapped lines makes sense, would be embarrassing for me if that was the case... Although, I would get over the embarrassment real fast if the car just drove like it should. I'm really hoping its not a third bad CPR.

Thank you all for the information, there are so many outstanding members of this community!

I looked at some old pictures of my '85 and it doesn't look easy to swap any of the hoses. The banjos on the CPR are 2 different sizes (6mm/8mm), so they won't swap easily there. The CPR hoses on the fuel distributor are far enough apart, with different rubber / metal tubing, that swapping there isn't easy either.

Was your K-Jet every running well? Did you or a PO have any of the hoses rebuilt? Perhaps the hose rebuild swapped fittings by mistake?

What is the history behind the three WUR's?

Original been sitting for years? Junk yard replacements with no know history?

If you have taken one of these things apart you know about the very fine stainless steel mesh on the input side. Let me assure you that fine tank rust will blow right through the filter and end up in that little filter. The result being control pressure at system pressure.



I took mine apart several times and it would work, then wouldn't work until I spent $210 (shipped) for a professionally rebuilt one. Installed and it came up right on the money on my pressure gauge.

https://www.deloreanautoparts.com/warm-up-regulators.html

Their web site says closed due to family illness but a very helpful guy. He doesn't rebuild the WUR's but stocks them from someone that does.

Be sure to research the correct WUR for your car. There are hundreds of them. Even the one you thought was original may not have been correct. You are looking for the last three digits of the number on the device. Mine was 066 and that was correct after research.

bobxyz said:

I looked at some old pictures of my '85 and it doesn't look easy to swap any of the hoses. The banjos on the CPR are 2 different sizes (6mm/8mm), so they won't swap easily there. The CPR hoses on the fuel distributor are far enough apart, with different rubber / metal tubing, that swapping there isn't easy either.

Was your K-Jet every running well? Did you or a PO have any of the hoses rebuilt? Perhaps the hose rebuild swapped fittings by mistake?

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I agree, the only way a swap could happen is at the distributor but it would still be hard to do. I don't know if the PO had the hoses rebuilt, it doesn't look like they were comparing to pictures that I've seen, and the history of the car is unfortunately very murky. Its hard to tell if the k-jet was ever running like it should. When I got the car, it wasn't running because of a broken fuel pump. Then the OD relay and lock-out switch were faulting causing the car to jerk in and out of OD in all gears. Once I sorted that out, the car drove alright but that is about when I started noticing the starting issues and some hesitations. I played with the idle screw next to the distributor for a while before finally checking my pressure and realizing there was no change in control pressure. Its totally a possibility that the fittings were swapped as from what I can tell the CPR was not original and the distributor is from a 260, so at some point there were a lot of changes made.

TestPoint said:

What is the history behind the three WUR's?

Original been sitting for years? Junk yard replacements with no know history?...

Click to expand...

The first CPR came with the car, unclear if it was original but seems to have been messed with. The recessed area/pin I've read you can adjust on the CPR that is next to the firewall connection looks to have been tapped with a hammer. From what I gathered from the PO the car may have been sitting a year or two so definitely could have had some damage. The second CPR was from a "running 204 turbo". The third CPR was actually from John at Delorean Auto Parts. I've checked and all the CPR's are correct for the car.

Lines were swapped. You all are geniuses. I can?t believe all the hours I?ve spent yelling at this car and that?s all it was. I?m over the moon, thank you all so much. Now onto the next project: suspension work. Time to cut those springs!! (Just kidding)