240 1976 b21f stuttering at highway speeds.

[Hootbot]

I had many breakdowns on a trip to my parents for xmas on Monday

The car drives totally normally in town but on the highway it stutters and dies

I initially thought this could be the overdrive acting up since it went away if I shifted out of overdrive but it was definitely an engine issue when it died on the side of the road, the car restarted and I was able to keep going but it persisted and grew worse and worse as the trip went on, the car stutters if you try and cruise on the highway at 65mph (3000rpm) if you persist in driving at 3000rpm in 4th or overdrive it will buck and backfire out the exhaust and eventually die. you can cycle the key and drive for awhile but it starts doing it again. I thought this could be a fuel starvation concern like a clogged filter but the problem paradoxically goes away if you drive faster (higher rpm)

Hard to really diagnose for me since it only happened after like 30 minutes of driving

It's most certainly rpm related since it did this in 4th and overdrive it would sometimes totally die but then start right back up and work fine for awhile, the car worked totally fine if you kept the rpms up but I did end up doing about 90mph for the last 30 miles of the trip.

I think the issue may be ignition related since it reminds me of the way a car behaves if you get moisture in the distributer cap. The engine will stop and then just start running again.

 

[oldschoolvolvo]

This sounds like what I went through with my kjet 242.
https://forums.turbobricks.com/showthread.php?t=170882

I'd check to make sure both fuel pumps (main pump and tank pump) are working and moving fuel. You can jump the fuses so they run without the car on (see link below). I'd also disconnect the input line to the main pump and verify that the tank pump is actually pumping.

Is the main pump quiet when running or does it buzz?

Good reference info:
http://cleanflametrap.com/transferPump.htm

 

[Hootbot]

Well I’m pretty sure the in tank pump is dead because the main pump groans when the fuel is low, it’s been like that since I bought it though and was working fine previously.

 

[Redwood Chair]

Midrange stutter does sound like bad intank pump or bad accordion feed hose.

 

[Hootbot]

So after looking at that diagram from the volvo manual it’s apparent that mu car being pre 1977 doesn’t have the in tank pump at all. Is there still a suction hose. It did this with a totally full fuel tank.

 

[hiperfauto]

A lot of early cars were updated to include an intake pump. If the hose feeding the main pump is coming from the side of the tank, it hasn't been updated. If the hose is coming from the sender, it's been updated.

 

[Hootbot]

A lot of early cars were updated to include an intake pump. If the hose feeding the main pump is coming from the side of the tank, it hasn't been updated. If the hose is coming from the sender, it's been updated.

It comes out of the side, I recall thinking it looked odd when doing the rear suspension.

 

[hiperfauto]

You may want to check the screen on the pickup tube. The filter can deteriorate and block the pickup tube intermittently.

https://www.ipdusa.com/products/21292/139926-in-tank-fuel-filter-strainer-140-164-1800-1972-genuine-volvo-688593

In order to access the filter you need to remove the large brass plug on the bottom of the tank which requires an odd size square tool. Grind down a 7/16" piece of square stock to fit or you risk damaging the soft brass plug.

 

[Hootbot]

You may want to check the screen on the pickup tube. The filter can deteriorate and block the pickup tube intermittently.

https://www.ipdusa.com/products/21292/139926-in-tank-fuel-filter-strainer-140-164-1800-1972-genuine-volvo-688593

In order to access the filter you need to remove the large brass plug on the bottom of the tank which requires an odd size square tool. Grind down a 7/16" piece of square stock to fit or you risk damaging the soft brass plug.

I presume you need to drain the fuel tank for This?

 

[hiperfauto]

 

[dl242gt]

Electrical stuff can be fuses getting too hot in the fuse box. I'v also had the main pressure pumps get intermittent after they run about 20 minutes or so. The pressure drops and the car barely runs or stalls.

 

[Redwood Chair]

In order to access the filter you need to remove the large brass plug on the bottom of the tank which requires an odd size square tool. Grind down a 7/16" piece of square stock to fit or you risk damaging the soft brass plug.

Or shim up your 3/8" drive extension with a strip of tin can and ease it out of there.

 

[planetman]

The tool in hiperfauto's picture grew legs and I had to make a new tool.

This time I ground down a short 1/2" extension to fit into the plug.

 

[Hootbot]

Im going to change the main fuel filter under the hood tomorrow since it’s okd af and i have one on hand. I’ll likely drive the car until the fuel tank is close to empy before investigating that plug. It’s a bit difficult for me to test this since it only did it after driving at highway speed for 30 minutes.

 

[Hootbot]

alright so this is what the fuel supply system looks like. No intank pump I think??

I changed the filter and test drove the car (with a low fuel tank) it worked fine for the majority of the test drive but started to stutter just at the very end.

With the fuel gauge reading empty now I'm going check out that in tank filter.

I think it's strange that it only happens at mid range speeds like 110km/h but not at lower or higher speeds, the car can be accelerated to red line around town through all the gears and it doesn't even hiccup, you would never know there were an issue if you didn't go for an extended drive on the highway.

 

[Hootbot]

So I removed that plug on the fuel tank (I just used some large channel locks sorry) and the filter appears brand new and the tank is nice and clean inside. I decided to shotgun the engine bay with all the good used ignition parts I had in the garage so new coil new cap rotor and wires and plugs went in just to see what happens. I also refilled the fuel tank with fresh premium fuel which probably did nothing.

This did not work and I filmed the test drive so people can get a better sense of the issue.

I'll likely be ordering a kjet test kit off amazon tomorrow if no one has a clairvoyant moment. Since I have no way to test the pressures ATM.

https://www.youtube.com/watch?v=c-5O5Up1vEs&feature=youtu.be