Troublesome 3.2 - Lack Acceleration
 

I'm hoping someone can help me solve an usual issue with a '84 3.2 installed in a 914 with stock Motronic FI.

First the problem:
The car lacks acceleration power. If I'm moving along in second gear (901 trans) and I open it up to WOT, the car slowly accelerates. It takes a good 75-100yards to accelerate from 2000-5500 rpm. I just recently drove a split window bus with a 2.1 Type1 engine and that thing was WAY faster.

Here's some data:
- Car starts fine. Turn the key, roars to life, no sputtering, hesitation or hunting.
- Car idles fine. Leave it alone and it sounds smooth and even.
- Car cruises fine. Mixture reading from a separate, independent WBO2 shows roughly 13:1 AFR.
- At WOT the mixture stays the same, perhaps slightly richer (12:1 or 13:1).
- At WOT, although it's not performing correctly, there is no misfiring, popping, or other noises.
- I roughly confirmed the ignition timing while parked. Around 10 degrees at fast idle (1300 ish rpm) and climbed to around 25 at 3000. This test could be done with greater accuracy, if necessary..
- Speed sensor and reference sensor are both new and adjusted to 0.8mm gap.
- Just pulled the spark plugs and they aren't fouled and look like they should with a good mixture. Not too dark, not too light.
- ECU was rebuilt by Specialized ECU Repair (PN: 0 261 200 050)
- Engine Number: 64E04961
- Adjusted WOT switch.

My Speculation:
It feels like the ECU isn't 'noticing' the acceleration and isn't advancing the timing or injecting extra fuel. I would expect the mixture to go slightly more rich at WOT. And the feeling of no-power/acceleration feels like insufficient ignition timing. I realize that ignition timing is handled by the ECU. That's what makes this problem so frustrating.



I know that's a lot of information and reading. I hope someone has a few more tests I can perform to try and nail this thing down.

few thoughts --

1) have you confirmed that you're fully opening the throttle when "stomping" the accelerator? I recall prior threads discussing how a mis-adjusted throttle cable can cause this behavior

2) have you confirmed that the wide open throttle microswitch is being activated at wide open throttle? This tells the ECU to richen the mixture and provide full power at WOT -- again, I recall prior threads discussing how to test/confirm this. I see that youve adjusted the WOT switch, but not clear that you confirmed it activates at WOT

13.1 is extremely rich for EFI at steady cruise.

check the throttle switch, maybe the ECU thinks it is still at idle.

Have you checked the distributor and cleaned up all the contact points?

I have a similar problem as yours... if you find a solution, let me know.

Just did that this morning. It's getting 100% throttle.

Yes, that's how I adjusted the switch. Held the throttle open with a prop rod. Rotated the switch until the ohm-meter read that the two top pins were connected. Tightened it down. Finally, confirmed at the ECU connector, the WOT switch is working correctly.

I'll have to confirm this then. I've been doing loads of testing and may have gotten confused.

Confirmed at the ECU connector, the idle switch is working correctly.

Not sure what you mean by contact points, the 3.2 distributor is essentially empty. But the cap and rotor are new. The centrifugal 'advance' mechanism is working as well. (Yes, I know it's not really an advance and understand it's purpose and function).

Just tested the AFM, voltage output varies from 0.25-4.5v as expected.

Nope, it's definitely at 13:1 or richer. But this is just quick test drives, so it may be rich during warmup, while the CHT is rising?

Weird. Is the slow acceleration linear? If so, probably isn't timing, AFM or vacuum as those would cause hesitation.

Does the car build revs normally by pulling on the engine throttle? Still think the most likely culprit is you're not at 100%. Have you pulled the intake off and verified the butterfly is fully open?

Otherwise (assuming linear acceleration and not throttle switch), you must just be running down a few cylinders.

Mine when warmed up doing a few test runs with a new chip was doing 13 at tip in and in the 12's at WOT. I don't think you're far off or too rich at WOT at 13.
Take an infrared thermometer and check the temps at each exhaust port to see if you have a cold cylinder. I would think if you're idling fine you're not down a cylinder. Each exhaust port should be fairly close in temperature.
At cruise you should be close to 14.7. When I'm cruising mine is in the 14.4-14.7 range. Warmed up at idle are you about 14.7?

Has it always performed like this?
Engine is a big air pump. Intake not blocked? No Brawny paper towels blocking intake ports an forgotten during assembly? What type of exhaust, possibly a partially blocked cat?

3.2 distributors don't do anything. It's just a rotor spinning that aligns with a post when the motronic ecu fires the coil.

Power in an engine is produced a lot easier then a lot of people think. You put in a certain quantity of air combined with fuel and it will produce a certain quantity of power. There are a few things you can do to reduce the power output but other than that the power is fixed to the quantity of air/fuel mixture.

You know the mixture which tells us a huge part of the situation that people don't know. (assuming the readout is accurate...) 13:1 is rich but 12.7:1 is a common number you used to see for max full throttle power when people were tuning carbs for drag cars. Assuming it doesn't go past that at full throttle I really don't see that as an issue. I would do a full throttle pull with a hard cut off and read the plugs to see if that jibs.

Assuming all that the mixture is as listed, on an EFI car that really leaves two choices:
- Massively retarded timing (advanced timing would be obvious from the pinging)
- A huge restriction in the air feeding into the engine.
Sure you could have something that keeps the combustion pressures from being contained but it would be really really obvious that something was massively wrong with the engine.

How did you check the timing? I would actually pull the #1 plug and confirm that the timing mark on the pulley and the flywheel reference sensor pin line up with the piston position.
As far as the airflow, I would make sure that the barn door in the AFM is moving freely and allowing a "full throttle" quantity of air into the intake. The air filter, the air filter housing, and the intake tract need to be checked for restrictions too.

-----------
A final thought is: Do you have a way to check the air/fuel ratio on both banks of the engine? If you are only checking one side you could have an issue only on one side of the motor but you would expect that kind of issue to be pretty obvious outside of WOT.

And as a last "bonus round" detail that I think isn't the cause of the current issue: I would look at what chip is in that DME and try a stock chip to see about getting the air/fuel ratio up where it should be.

I understand the 13.1 is a steady cruise which is too rich.

I don't know if this ECU has this function but most have a "default" or safe mode of mixture/timing setting that if it does not get an input it needs or it thinks some thing is wrong it goes to a safe default mixture and timing.
had this happen on a Volvo I had. very very bad acceleration but it would cruise fine,.

check the temp sensors.
check the wiring from the AFM to the ECU. if an AFM is "unplugged" I t will put an ECU into safe mode.

Stupid question, have you changed your fuel filter lately?

Yea, that's one thing I haven't seen mentioned yet: fuel pressure.
Possibly just enough to keep idle but not enough to create acceleration? Pump, filter, regulator... the usual suspects check out?

My first 911, which I still have though not anywhere NEAR stock, had CIS. CIS is ALL about fuel pressure. I got a load of contaminated fuel and it killed my fuel filter. I had to change it twice despite, full fuel purge and what not.

If it ain't fuel, it's pressure or spark....

low fuel pressure or lack of fuel making it run rich??

maybe too hi a pressure.

I would think a low fuel pressure or volume would make it 'buck' rather than accelerate slowly - also, this should show up on the AF meter.

A weak or misdirected spark could cause this - enough energy to spark the plugs under moderate conditions like idle or cruise, but under higher cylinder pressures it finds another path? I've certainly experienced similar conditions when I get moisture in the distributor cap, or plug wires that allow the spark to escape.

I've also seen it when my spark plug gap is too large, encouraging the spark to find other paths to ground.

BTW, how many of us did the test? In second gear even my tired 3.2 goes from 2000RPM to 5500 in well under 3 seconds even without WOT. it sure comes up fast that's for sure.

Chuck.H
'89 TurboLookTarga, 430k miles

i would try to verify timing Is at least advancing.

you could line the rotor up #1 and make your own mark on the pulley if there isn't one. all you want to do is see it advance.

if it does not advance that may not be the only issue. like I said, it could be in a "safe mode" that restricts timing and makes it run rich to protect the motor.

It's a "dumb" ECM. It doesn't have that feature.

Maybe time to call the ECM rebuilder and have another unit sent.