'85 944 Acceleration Hesitation
 

When I step on the gas pedal hard, the engine drags and sometimes sputters before accelerating. I have made an audio recording. It can be found

HERE

I have changed and gapped the plugs. Replaced the distributor and rotor cap. I suspect the fuel filter. I have no idea how old it is or if it's ever been changed at all. Or possibly the plug wires. I'm just hoping to get some ideas about where to begin. Hoping someone has had this problem and knows what it might be.
Thanks in advance.
Ian

If you haven't a clue about about age/condition of the fuel filter, its a good place to start. Relatively cheap too. Then run a couple of tanks of gas with some techron fuel injector cleaner. You can also disassemble the AFM and check to see if the wiper track is etched badly, and if so adjust the wiper to a fresh portion of the track. Additionally... How does your air filter look?

You can find more info on AFM 'cleaning' in the garage shop manual at clarks-garage.com

Well, I took apart the AFM according to the tut's and there were some grooves in the plate, although they didn't seem too serious. I bent the wiper a little and a slight squeak went away. I put it all back together and it seemed a little bit better but that may have been selectively wishful hearing. It is still doing it. It just simply has no power in low RPM's. I live on a hill and I have to over-rev to get going up the hill when it's cold. It still does it when it's warm but not nearly as bad. I will go ahead and replace the fuel filter but it really doesn't seem like it's not getting enough fuel. I say that because it seems to be backfiring. That is what I mean by sputtering. You can hear it in the audio recording. I am no mechanic so I could be all wrong.

Oh, and the air filter is good. Thank you for all the great advice.

Sounds like you have a vaccuum leak. You should buy some new hose clamps and new universal vaccuum hose for the small lines. Then re-seat all of the other larger hoses.

If that doesn't work, check your catalytic converter to make sure it hasn't fallen apart inside and is clogging your exhaust system.

Lastly, it could be a faulty knock sensor causing your timing to retard.

no knock sensor on an '85

I had these symptoms too...checked vacuum lines & gaskets, changed filters, checked inlet screen of fuel pump as well as fuel tank screen, checked voltage at fuel pump, adjusted AFM track, cleaned injectors, spark plugs, yada, yada...

then noticed a slight dip in fuel pressure when revving the engine (but normal pressure at idle). I changed the fuel pump and all is well. the bad pump had only a few thousand miles on it...go figga !!

Sorry, forgot it was an '85...no knock sensor. One other thing that gets overlooked is the rubber boot that connects the AFM to the throttle body. These can get cracks in them, especially on the seams.

Pulling the fuel injectors and getting them cleaned is one of the best upgrades that you can do for these older cars. I did it for my car when it had 85k on it. Now it has 146k and I am going to do it again. Out of all the mods that I have done to my car, having the injectors cleaned was the most noticable.

I thought you couldn't clean them. I was told they simply must be replaced and they are fairly expensive. Is it something I can do myself or do I need a shop to do it?

Fairly easy to remove. Most large NAPA shops can clean and rebuild them for $25/injector including parts.

Procedure:
Pull fuel pump fuse.
Start car and let it run till it stops. (repeat if necessary)
Remove fuel lines, making sure to catch any residual fuel w/rags and bowl.
Disconnect Bosch connectors to fuel injectors.
Remove fuel rail (usually 6-8 screws holding it to the head) CATCH ALL WASHERS BETWEEN RAIL AND CYLINDER HEAD
Injectors come out attached to fuel rail.
Remove clips holding fuel injectors to fuel rail.

The injector tips will be very dirty. Simply spraying them down/soaking the tips in throttle body cleaner should make a world of difference. If you are going to clean crud around where the injectors seat into the head, be very careful not to knock any crud down the holes. I used pieces of duct tape to lift the dirt off the cylinder head.

Good luck and remember to take pictures and post them. I forgot to do that when I did it!

new injectors seals are cheap and here are detailed instructions:

http://www.pelicanparts.com/techarti...ctor_clean.htm

Okay, so I listened to the audio. Here are some thoughts:

1) The 'cough' in the intake is noticeable, as is the slow response to RPM climb. Usually when you get backfire in the intake, it's air/fuel mix issues. So, a vacuum leak would definitely be suspect, since the air/fuel rations are determined somewhat by the Lambda sensor in the exhaust. If you have a vacuum leak, it will take a "brief moment" for the sensor to pick it up in the trailing exhaust stream, and the DME to adjust your injector duration to comensate for all that "fresh" air. Thus, momentary hesitation.

2) I'd run a complete tune-up on the engine: plugs(you've already done, so skip), ignition wires, cap/rotor. The works.

3) Those pesky vacuum line "T's" always crack! They go through lots of heat-cycles on top of the head/below the intake manifold. Change out all those 1/4" vacuum lines and T's. They're cheap, and the time is worth the trouble (Yes, I'm back to vacuum lead, again!)

4) Very scary thought: if you're intake valves/valve guides are severely worn, air/fuel gases will escape back into the intake manifold and ignite/pop, making a backfire sound. How's your compression? Burn a lot of oil over the course of oil changes? Lousy fuel economy?

There are probably some other ideas........

Good Luck!

Just another thought, as I finally got around to it today and it made a noticable difference.

Clean the throttle body out. I had a bunch of gunk/tar/varnish (whatever it is that collects in there) on that butterfly valve in the throttle body. Remove boot, spray for 10 secs while moving throttle, reattach boot, start engine, run for a min, repeat. I did this about 5 times (till I grew tired of it).

Like i said above, noticable difference. Specifically the response from around 2.5k rpm and up. I guess 18 yrs and 84k miles can add some performance inhibiting gunk on the throttle body internals.