No throttle response on 81

[WFBT2]

I've run out of ideas so it's time to punt. 81 w/FI starts with no problems, runs smooth at idle but bogs down when I hit the throttle. RPM's will increase if I turn the distributor but not with throttle. This is a car I got as project with the engine removed so I'm not sure if I've missed something. So far I've removed and cleaned gas tank
- all new fuel lines, pump and filter
- cleaned out fuel rail and replaced fuel lines to injectors
- swapped AFM, coil and temp sensor
- installed new cap, rotor, wires, plugs, magnetic pickup, ignition module
- removed plug in front of cat to check for obstruction, no change
- double checked timing, TDC, cam timing, and rotor pointing to #4
- pinched off fuel return and engine dies
one odd thing I did see today was the RPM's will increase by 500 when the timing light is on,(with trigger pulled).
any suggestions on fixing this would be greatly appreciated,
Thanks

[So Cal Mark]

have you checked the AFM to make sure the flap moves and doesn't stick? How about the intake boot, no cracks?

[2ndwind]

I presume you plugged the vacuum advance when timing it to 10 deg, BTDC. What was your timing light hooked up to for power?

[WFBT2]

Checked AFM flap and swapped in my spare, no change. Also replaced vacuum advance diaphragm and the rod does move when I first hit the throttle. The computer has also been changed. The timing light was hooked to the + side of the coil and grounded to a fender bolt with pickup on #1 and 4. Also could not find any leaks on the intake boot or hoses.
I was considering putting an injected 2L in my 71 but even dual carbs might be less frustrating than this. I guess tomorrow I'll troubleshoot wiring on the AFM flap.
Thanks for the help and keep those ideas coming.

[76was124]

Random thought in no particular order.....

When you say it idles okay, is it perfectly smooth or do you see a little shake?

Did you confirm all the timing marks are aligned on the cams and crank?

How about valve clearances?

When you turn the distributor and the rpms increases. did you keep turning it until the rpms started to decrease again, and then leave it as max rpm and try the throttle?

Are spark plug wires all on right cylinders and all firing?

Which way are the spark plug connectors pointing out of the distributor cap? Towards the drivers headlight, passenger headlamp, or towards the firewall?

Did you do a compression check on the cylinders?

[spider2081]

Are all the ground wires connected to the engine. There is one on the passenger side that I think grounds through the exhaust cam rear cover stud. There are 2 on drivers side that ground through the throttle body rear 2 mounting bolts.

I would also remove the black plastic cove on AFM so you can see if the flap is actually moving from air flow.

Have you measured the vacuum with a vacuum gauge??

After engine is running have you unplugged the cold start valve electrical connector?

[GeorgeT]

Throttle Position Sensor adjusted correctly?

[wizard124]

Remove the plug at the AFM. Inspect the individual connectors to see if one has been pushed back. I had one that was causing a rough idle. Possibly not sending the "more gas" command to the ECU.

[WFBT2]

I haven't tried unplugging the cold start injector and will check the AFM flap and wiring soon, but it will have to wait for a few days. The weather has turned to snow and the car is parked outside.

[kauboi]

I presume you plugged the vacuum advance when timing it to 10 deg, BTDC. What was your timing light hooked up to for power?

not to hijack, but I cant find a reference in the service manual to plugging the vacuum advance when setting the timing, and I'm about to smog test mine...

[Zaffer]

Interested in the ideas here as I'm having a similar issue. Rebuilt AFM, New fuel pump/filter, new intake boot, New wires/rotor/cap, new dist. pick-up and module, and still getting the same issue as you.

I have also seen suggested that it could also be faulty injectors (leaking, clogged, poor spray pattern, sticking open/closed). You may want to check the spray patterns to make sure everything is good on that front.

[spider2081]

Have you checked the temperature sensor in the coolant "T" for proper resistance? Have you checked the connector for that temperature sensor. Both the sensor and the connector are known to cause strange problems.

[narfire]

OK I'll throw one out there..... Under the black top on the AFM is an arm that moves in an arc over a piece of material (not sure what it is made of) but anyway over time this will develop a warn strip and the engine can stumble. I had something similar and read here on the fix. Basically after collecting a bunch of band-aids, use a box cutter to carefully cut the seal between the black plastic and aluminium housing. Loosen the screw on the pivot shaft of the AFM, slide the assembly up or down so the pick ups are running on new material. The pick ups only have to move a mm at the most so kind of a delicate operation. (bend the arm perhaps?)
Good luck eh...
Chris

[WFBT2]

I was able to work on the car yesterday. The AFM flap is moving when I hit the throttle so I started working on the fuel rail. Swapped out fuel pressure regulator and now engine doesn't run so will be buying new regulator before anything else can be done.

[alsgro]

Hey there, WFBT2. Did you ever get this sorted? I'm having the exact same issue right now. The car had been sitting for a few years, so I had to do a few things to get it to start. Replaced the pigtail goin to the T-sensor and had to cut out the old in-line fuse going to the fuel pump and replace. New fuel pump, too. Changed the oil and flushed the coolant.

Now it starts up like a CHAMP. Idles great. Gets warm and the fan comes on as it should.

But if I blip the throttle, it bogs down and sounds like it wants to stall for a 1/2 second. Then revs normally. If I apply gradual throttle, it'll rev just fine. But if u give it the beans, there's no response. My AFM flap seems to be moving ok, too. So was wondering if you ever got your issue sorted.