Alright guys I need a little extra wisdom for the problem I am having. My car ('73 2.0L FI) has hesitation on acceleration. Sometimes you can barely notice it and sometimes it completely refuses to gain speed and other times it just feels sluggish. It doesn't necessarily run rough, just hesitant an sluggish. One day I might drive it without any issues and the next it starts acting up again. It is not heat related because it will act this way with the engine cold or hot.

-I have tried changing out trigger contacts, I also cleaned up the distributor
-Ground wire in Distributor is still connected
-I replaced the CHT
-I have changed out the TPS with no success
-Dwell and timing is on spec
-I adjusted the valves
-Distributor cap and rotor were replaced
-I played around with the spark plug wires and it doesn't seem to make a difference.
-Fuel pressure is good at 28 psi
-Fuel sock in tank was replaced 2-3000 miles ago and filter was changed not too long before that
-Coil and condenser replaced

I have probably done some other things but can't remember it right now.


Another note that I should probably include is that when the car is acting its worse, when it doesn't want to accelerate at all, I sometimes get the slightest backfire out of the exhaust. Would this more than likely point to the ignition system?

I guess the next things to do on my list would be

-Replace the spark plug wires
-Replace the points, although they look fine
-Change out fuel Filter

Anything else I should look into? Anyone have any thoughts on the next steps I should take? I appreciate any and all help!


Oh and a picture for shits and giggles!
Click to view attachment

it sounds like its running rich. all the hoses new? maybe a leak? possibly not enough air?
ideas that i tried and made me narrow down my problem where unplug the mps, does it run better/worse? unplug the decel valve from the bottom of the air intake better/worse again? advance and retard something to check out.
i'm sure plenty of people will have good advice but something to look at until they chime in. maybe?

I have replaced all vacuum and fuel hoses since getting my car back on the road last october. I should also mention that the car has Bowlsby FI and ignition harnesses on it so the chances of it being old and brittle FI wires is unlikely. However the fact that it comes and goes makes me think a connection somewhere.

Fuel pumps on it's way out or the regulator is sticking would be my guess.

Hmm I changed out the fuel regulator and that did nothing and my pump was a newly rebuilt Bosch unit when I installed it so I'm not going to put my eggs in that basket even though I have an extra if I need it. I think you might be onto something with fuel though. It could be starving for fuel. I'm going to try to change out my filter and see if that does anything. Before I fixed this car up it was sitting for a while and who knows what was in the system when i originally changed it out. Plus I've had the tank in and out a few times, plus 7000 miles later, the thing could be clogged. I'll change it out and I will respond with the results!

Test your vaccume canister on the distributor, and your MPS to see if they hold vaccume. Mityvac works good for that. Double check your wireing on your coil.

could be rust in the gas tank clogging up your brand new filter and sock? i've never experienced this but have read about others.

good luck and let us know what you find!!

My problem was rust in the tank that formed over the winter in a heated garage.

I chased many other items down but it was the tank.

You mention that you changed the CHS. Did you get the right one? I thought I did, but I am still chasing down either the right sensor, the spacer, or both.

What I would give for an 017 CHTS? Maybe a kidney? Well, no, but that sensor is a ball buster to get it right.

J

I had a similar issue, then it got prevelant fairly quickly, loose wire.. re: coil oriented.. the wire that was losse did not feel or appear to be loose but that it was obvious after that was the fix..

Well I am still having this problem. I replaced the fuel filter (which badly needed to be replaced) and the problem was still there. I then checked the fuel pressure while revving the motor and it remained at 28 psi so that eliminated the pump. I also vacuumed checked the advance on the distributor and it passed that test. Unplugging the TPS did not solve the problem either. MPS held vacuum wonderfully. I replaced the points too. Since I was running out of options I then pulled all the plugs and at least two of them looked too rich. So I moved onto the injectors... It turns out that three of my injectors we not closing completely which meant they were squirting fuel full time. I replaced them and ensured that they were all working properly and now I get a hunting idle on top of the accelerating problem. This suggests that the mixture is too lean on idle or all the time??? I tried to fix one thing and it makes the problem worse. Tonight I checked the Intake Air temperature Sensor which is a secondary sensor and shouldn't have too much of an effect but I checked it anyway. I got 240 ohms @ approx. 85 degrees. This seems to check out. I also plugged off the fuel line to the cold start valve to make sure that wasn't leaking and of course, that didn't solve the problem.

Right now I'm thinking I have a fuel mixture problem somewhere. I've checked and double checked just about everything. Could the ECU have gone bad and cause some of the drivability problems I am having? If not, what else should I look into? Any help is appreciated at this point.

Did you check the mechanical advance on the dizzy? Just something else to eliminate.

The timing mark would move as I revved the engine when setting the timing so I assume the mechanical advance is working properly?

Hey Doug,

Thinking out loud, but I had some similar problems. Just cause it may be one of these things, I will list them.

Rusted tank - Had to completely pull and treat it with POR15 System

All new fuel hoses and filters after having rust in the lines

I had the backfire issue. Plug wires were wrong. 1 is up by the fuel filler neck, then follow zundfolge

I had the no acceleration issue with backfiring - it definitely was the coil center lead coming loose 3 times

Check the decel valve to make sure the hoses are snug

Timing should march from TDC to 27BTDC as you get to 3500 rpm - Any messing with it and NOT getting it right is death to acceleration

Points should be 017

Dwell should be 42-44

Fuel Pressure Regulator must be 29.5 - 28 is too low, and it may be adding to the problems you are having

Hope one or several of these works!

Good luck!

John
avidfanjpl

John, where do you get 42 degrees of dwell? The factory manual says 44-50. Ideal is 47. Three people told you that in your thread, yet you choose to not beleive them.

I'd make sure the advance plate in the distributor is moving smoothly. Take off the distributor cap, connect a Mity Vac to the advance dashpot and make sure it moves when you pull a vacuum and then goes back when you release it.

It could also be a bad condenser, or as others have pointed out the wire to the points could be shorting.

I agree about dwell, double check that. Do you think there might be a pinched fuel line under tank that getting pinched while driving? Maybe a bad electrical connection for fuel pump, that is intermitant? Best of luck.

And you are right!

I checked dwell twice yesterday. 44 degrees both times.

Car is running HARD!

Thanks!

J

Make sure the harness is securely plugged in the ECU. Remove it and reinstall it. Make sure the small ground wire on the dizzy plate is in good condition. ECU could be failing. Borrow one from someone. Make sure you get the exact one. Mixing these up will make headaches.

I've been meaning to update this thread. About two weeks ago I took everything off the top of the engine. There was oil residue covering everything from a previous oil leak and dust still covered everything from when I painted my car so I took this as an opportunity to clean everything. Everything was clean and I made sure everything was in spec and working as it should as I put everything back on. I checked all connections, looked for any possible shorts, etc. After putting everything back together, the problem was still there...


So then I wanted to test out my lean mixture theory. I'm running the 012/003 CHT on my '73 FI system which should make the mixture richer. I added a 270 ohm resistor inline and the problem got better but was still obviously there. I added a second resistor inline and the problem is almost completely gone. This confirms that my mixture is too lean and I have to compensate by having a high resistance value being sent to the ECU via the CHT. I've tried adjusting the mixture via the knob on the ECU but it doesn't seem to do anything. It almost seems as though the ECU mixture is broken and set on full lean. Possible? I'm able to drive the car with the current setup but would like to find out why it wants to run way lean.