Evening. Been a little while since I've posted a question, but I have a car that I just wanted to be sure on the diagnosis on, since I think the fix may be a little expensive and I am not dead certain since it has been a little while since I've fixed this ever common k-jet oddity.


Ok, '83 244TIC.

Runs fine, no vac leaks, wiring problems, fuel delivery good/fine (new chassis pump, recent filter, no rust in lines or tank, recent good 740T in-tank pump), idles quite smooth cold and hot. No complaints really. Good solid car for the most part. Thermo-time switch for cold start injector is new (found an NOS one lying around and put it on the car).


The car starts right up stone cold and runs just fine.

Line pressure is a solid 85psi and just fine running under load or not.
Control pressure/warm up regulator works fine and follows its chart last I checked it, and given that it is getting colder out and they usually fail cold, I'm inclined to think it works.
I set the fuel mix recently after not having touched it for several months and it was right where it was before and behaving as it did before, so I think nothing is really out of whack on the fuel side.

The car starts right up hot if it has been maybe 5 minutes or less.

Problem:

Say you stop by the grocery store or go somewhere where you might be out of the car and back in it in 20ish minutes? It starts up rather slowly and grumpily an runs kind of rough, sort of hard to tell if it is too rich or too lean exactly, but it isn't right. You rest your foot on the gas for a sec and it clears out and goes right on like nothing is wrong after a few seconds.

Hints:
Accumulator is old and used/original, but it is the type with the screw in the back and doesn't leak. Most I've replaced leak or really don't hold rest pressure.

Fuel pump check valve is old and used, though the pump is new.

It seems to have gotten a lot more notable after I put a considerably warmer coolant thermostat for winter in it. I went from a 71C to an 87C, so I pretty big jump...160-188F. I have not really changed anything else.

I did lower the line pressure from 97psi to 85 around the same time, but that was the only other "change" and this didn't start happening until not long after I changed the coolant t-stat.

I have not checked rest pressure recently, but IIRC, I think it may not hold it quite as long as it should as per the book.


When I was working on it, I had the fuel pumps jumpered for a while with the car not running and *thought* I heard a slight whine of fuel going through the fuel dist/lines like when the injectors are slightly cracked open, but I have not been able to reproduce it at all, and I really would think it would run like crap cold if the injectors were leaking.

My big question here is, I think it is an accumulator or fuel pump check valve, but there is any way a leaking injector could explain these symptoms (they didn't leak when last I checked them,but that was last winter)? I think I'm getting some vapor lock in the fuel lines from the car sitting and heatsoaking (which 10-25 minutes is a pretty perfect amount of time for that to occur) and at the same time the car won't hold rest pressure quite long enough to prevent the fuel from boiling in the lines and making the thing not start up quite right. It isn't like it is flooding out or waaay too lean either since it clears itself out pretty quick (5-15 seconds?) and runs like nothing ever happened, I don't even think it dies if you let it idle its way out of it, just runs kinda crappy for longer and then goes away.

I've fixed accumulators and check valves that caused this symptom IIRC (and it was no fun to diagnose that the first time as people would describe it to me and I'd have to set a timer and wait for the car to do it with the pressure gauge on it often and eliminate the injectors) and there aren't many k-jet cars that people want me to go through and fix nice left on the road, so it isn't quite fresh. The car has new (or recent non-leaking) o-rings on the injector holders, so I kind of like to not disturb them if I can leave them in the car and don't need a reason to be taking injectors out. I think the symptoms fit the accumulator or check valve too because if it had a leaking injector, I'd think it would run crappy cold, which it definitely doesn't. So, any further ideas before i go ahead and test the rest pressure and declare it an accumulator or check valve? Can a slightly leaking injector actually cause the rest pressure to drop off a lot? I want to say "no" unless it is the cold start injector, as the main line ones wouldn't be able to drain the fuel dist down if it were just one of them I want to say?

I suppose another possibility is that I need to adjust the resting position of the fuel dist arm? I've had to do that before, but that one is a real rare one.

My B21FT would do this exactly. I fixed it with a small piece of rubber-like substance (went to my local industrial gasket shop and told them what I wanted to do).

What I determined through testing was that the injectors were fine, the control pressure regulator was fine, the fuel pump was fine, the fuel pump check valve was fine, the fuel pressures were all fine... but the rubber sealing surface on the line pressure regulator had hardened up and deformed so badly that it wouldn't seal. Rest pressure would drop to zero within a couple minutes of shutting off the engine, and when blocking in the fuel distributor I could get the rest pressure to stay up for an acceptable amount of time.

I don't know about you, but I felt that I needed the tools for this diagnosis so I built them. I built a pair of adapters from spare banjo bolts for the fuel distributor so I could check line and rest pressures and control pressures, I built a plugged banjo bolt for the fuel distributor outlet, and I found the proper hose under (I think) an LH 240, to connect between the fuel filter outlet and a 1/8" NPT pressure gauge. With these I was pretty much able to test it all.

Another thing to consider is how freely does the fuel accumulator release it's pressure? Before I changed it, mine would let the pressure drop to near zero sometimes and would then suddenly release. When removing a fuel filter this got interesting...

A simple test, something I never thought to try, would be to insulate those long fuel lines so that they don't pick up so much heat when you shut off the engine. You never hear of this happening with anything but a B21FT, so that leads me to believe that it's either in the routing of the lines, the material of the lines, or the length of the lines.

Well, I have a k-jet compatible gauge (on loan to a good friend, but easily obtained) and a plug banjo.

I did test the check valve and it is fine last night. Scratch that.

Seems reasonable. I also have an accumulator lying around somewhere or other. I will do further testing and report back. I think mine does stick and let the pressure go down or doesn't work all together.

Changed the line pressure regulator valve seat as per Matt's issue. No change, though mine was fairly dried out at 260K miles.

Changed the fuel accumulator with one that I had sitting in oil forever that came off a good running 85 turbo parts car. Went out and hammered on the car tonight, pull it in the garage. Wait 25 minutes. Whoosh, springs to live like nothing. Being the skeptic that I am, I went out and hammered on the car some more, idled it a bit to let the turbo cool down and get everything good and hot and waited an hour.
No problems. Springs to life just like you just shut it off. I'm going to declare it successful. I think it even runs a little better, not that it was especially bad before, but now it seems even a slight touch smoother. No idea.


In the name of science I decide to have a little fun and smash my old accumulator against a brick a bit and fuel starts pissing out of it pretty quick with it facing mostly upward. Must have been good and stuck. Maybe it worked some of the time too who knows. Was good to have some seeming closure on the issue whatever the deal was..whether it was some combination of line pressure regulator and accumulator it seems.

Yahoo!

Smashing stuff in the name of science always gets my vote