'84 Carrera 3.2 sudden engine miss and loss of power

[Fab64]

Hi all,

I've had this car since this past August, 52,700 miles. In September, just after purchase, I had a full service done (including cap, rotor, plugs, plug wires, etc.). I've put about 2,000 miles on it since then, and it has been running perfectly. It was in the shop this past Thursday morning, but just to replace the engine lid shocks. It was fine on the way home from the shop. I took it out for a drive yesterday, again it was fine. I drove it 13 miles up to Cars & Coffee this morning, running fine. It was fine when I left there. About 4-5 miles from home, at 70 mph in 5th gear, it felt a little odd, lacking power. When I exited the freeway, I could both hear and feel that it was missing. I slowly drove it the 2 miles home, and into my garage. My first thought was maybe the tech knocked a wire loose while installing the shocks(?). I've checked everything I can think of, but nothing seems to be loose or out of place. Does anyone have any suggestions for where to start looking, common issues, etc.? Thanks for any ideas.

Roger

[proporsche]

1st thing would be ....is your fuel gauge working , does it show correct fuel amount..
Ivan

[Fab64]

Originally Posted by proporsche

1st thing would be ....is your fuel gauge working , does it show correct fuel amount..
Ivan

Yes, it shows just over 3/4 full. I filled the tank on March 9th, and have driven 75 miles since then.

[proporsche]

and now when you start it what does it sound like?..does it run on all cylinders?

[Fab64]

It starts normally, goes up to about 1050 for 30-40(?) seconds (normal), then settles back down to normal (around 800), and doesn't sound like it's missing. But blipping the throttle a few times feels not as responsive as usual, and the idle drops back down to between 500-600, with a strong smell of fuel in the exhaust.

[isby]

When they did the full service, did they replace the speed/reference sensors? Also, did they do a fuel injector service?

[proporsche]

ok, can you check if your air booth to the air flow meter clamp is tight? do you know which one or should i show you..
also in the engine compartment are 3 Bosh plugs on the left side check if they are all in
if you can make a a video ..that would help too

[Fab64]

Originally Posted by isby

When they did the full service, did they replace the speed/reference sensors? Also, did they do a fuel injector service?

The invoice doesn't mention a fuel injector service. And the only sensor replaced was a temp sensor 930-606-915-00.

[Fab64]

Originally Posted by proporsche

ok, can you check if your air booth to the air flow meter clamp is tight? do you know which one or should i show you..
also in the engine compartment are 3 Bosh plugs on the left side check if they are all in
if you can make a a video ..that would help too

Are you talking about these three plugs? They're all the way in.



Do you mean this clamp, at center top? It is tight.

[proporsche]

ys that clamp ..looks tite also the 3 connector look plugged in right?

[Fab64]

Originally Posted by proporsche

ys that clamp ..looks tite also the 3 connector look plugged in right?

Yes, they're tight.

The passenger side shock is behind the air filter housing, and it looks like at least the housing lid has to be removed - is there anything behind the housing that might be significant?

Can a speed/reference sensor suddenly go bad? And is there a way to test it/them?

[proporsche]

nothing on the right side...the only thing i could think of on the reference sensor is if the bracket is loose but..your mechanic would most likely not touch that stuff..it does not get loose...
the temp sensor does not go bad suddenly...it is new...
any rain in your neighbourhood?

[Fab64]

Originally Posted by proporsche

nothing on the right side...the only thing i could think of on the reference sensor is if the bracket is loose but..your mechanic would most likely not touch that stuff..it does not get loose...
the temp sensor does not go bad suddenly...it is new...
any rain in your neighbourhood?

It rained earlier this week, but not since Wednesday (before the hood shocks were replaced). And I haven't had the car out in the rain at all.

If the Reference Sensor was going bad, or misadjusted, would the engine still run? Is it possible a bad sensor could cause a miss?

[proporsche]

yes there is a adjustment which has to be precise but i do no think the mechanic would touch that bracket.the temp sensor is away from that...make a video if you find the time
Ivan

[Fab64]

Originally Posted by proporsche

yes there is a adjustment which has to be precise but i do no think the mechanic would touch that bracket.the temp sensor is away from that...make a video if you find the time
Ivan

Anything specific? Or do you want me to pan the entire engine compartment?

[proporsche]

i would like to see the running of the engine that is all ,to see the behaviour..

[917_Langheck]

Originally Posted by Fab64

It starts normally, goes up to about 1050 for 30-40(?) seconds (normal), then settles back down to normal (around 800), and doesn't sound like it's missing. But blipping the throttle a few times feels not as responsive as usual, and the idle drops back down to between 500-600, with a strong smell of fuel in the exhaust.

That sounds like a fuel metering issue. If there isn't a miss, then the plugs are firing, but the fuel ballance is off or one or more of the injectors aren't turning off (that would be a ecm issue).

[Fab64]

Originally Posted by 917_Langheck

That sounds like a fuel metering issue. If there isn't a miss, then the plugs are firing, but the fuel ballance is off or one or more of the injectors aren't turning off (that would be a ecm issue).

Beginning on page 240-10, the Bentley manual describes how to (at least, partially) diagnose the fuel injectors. Unless someone has a better idea, I will start working on that. Hopefully, that may point me in the right direction. I will report back with my findings. Thanks.

[917_Langheck]

The first place to start is to make sure all your ground points are clean and not acting as resisters.

The fact that it doesn't miss at idle but does elsewhere is interesting.

[Fab64]

Originally Posted by 917_Langheck

The first place to start is to make sure all your ground points are clean and not acting as resisters.

The fact that it doesn't miss at idle but does elsewhere is interesting.

Well, I'm not sure about the miss at idle. It doesn't sound exaggerated, but maybe it's there. Give this a listen and tell me what you think:

https://youtu.be/W_QUZFqz-4U

Here's the long one, with startup, rise to 1050, drop back to 800-ish, etc.

https://youtu.be/2ZneEaYo7QQ