Posted this last year on the list and didn't get any responses. Hoping I will get luckier this time!

I have an 87 with Autothority Mass Air Flow. At all RPMs while accelerating it started hesitating last year. After recalibrating the MAF at Autothority and reinstalling MAF, it ran great again. Unfortunately, it has started again. Autothority shipped a brand new unit but the car continues to hesitate. The shop I use (Akers in Seattle, WA) suggests switching back to the factory unit (which will cost me a factory unit, of course). I am wondering what else could be causing this problem.

Appreciate any suggestions/insight/help. The car has just had the full service/valve adjustment as well. dwassmann@earthlink.net

 

Totally unrelated to your MAF installation, but is your Cylinder Head Temp sensor the old single wire version or the updated twin wire version?

When the old single wire unit fails to ground, very similar hesitation can occur - erratic sometimes fine, sometimes terrible.

It's a definite update required if it is still the old version.

Just a thought.

 

Christian,

Thanks for the feedback...how do I tell if I have the single or dual head temp sensor wire? Where do I look?

 

David, there are three harness connectors to the left of the engine - they are mounted on a slim vertical panel, one above the other. The head temp sensor is connected to the top one.

The wires connecting to the panel from the left with the plugs are not at issue. Instead you need to check the sensor wires running from the panel-back down to the engine. I can't remember how easy it is to tell whether it is single or twin.

This is a pretty common problem with these cars, so do a search here on it and at Pelican Parts for previous experiences.

Hope that helps.

 

I've checked the cylinder head temp sensor and it was actually replaced...it is the new one so this is not the problem.

Any other suggestions from anyone on resolving this problem? My next step is to spend $$$ to put the OEM air flow unit back on at Akers and see if that fixes the problem. If so, it is the aftermarket unit.

I did note that the o2 sensor is disconnected. Could this be causing the problem? I didn't think so because it has been disconnected since I've owned the vehicle (4 years without problems until this spring).

David

 

Is a MAF the same as a "hot film type" as I had a similar problem?

 

Yes, it is of the hot wire/film variety. <a href="http://www.autothority.com" target="_blank">www.authority.com</a> is the website for their product.

How did you resolve? Or did you just give up and punt? THe autothority folks tell me this is very, very rare and have seemed pretty good so far. Plus, the car ran fine for over three years...so I am wondering what changed. I was just out there now checking grounds, wires, etc. but it is still running as if it had some bad gas.

 

Note the website is <a href="http://www.autothority.com" target="_blank">www.autothority.com</a> for the mass air flow sensor.

 

In the end it turned out to be a poor connection - the connector from the MAF to the interface unit was breaking down. Seems simple but it took 6mths to resolve
The symptoms were exactly as you describe.
Does your car idle OK?
Does your car run OK at full throttle?
The MAF unit used in my conversion is a Bosch unit (used on Audi`s apparently) and should last 100000 miles at least.The technology for these units is reliable - they are used on many modern cars with low failure rates.They are, apparently susceptable to contamination - do you use an oiled air filter?
The interface units are also apparently simple electronicaly and should also have a very low failure rate.
Does the 87 use Bosch hammer diagnostics ? Mine showed an open circuit fault at the air sensor (which of course had been replaced by the MAF but the ECU would not know this) which apparently is not possible as it means the air sensor was disconnected and the car would not run but would in fact be consistant with a poor connection.
The signal to the ECU is in mVolts so a good connection is critical.If the ECU does not receive a signal from the MAF or a corrupted signal you will experience the symptoms you describe.

 

Thanks for the excellent feedback. How do I test to ensure that there is a solid connection to the ECU? I checked wiring and all looks ok. Everything looks properly connected.

Yes, I do have one of those aftermarket "oiled" air cleaners (K & N). How would that contaminate the aftermarket flow sensor? The new unit that was sent has a brand new filter so I don't think that is the problem.

My guess is that something along the way has gone wrong. The problem is, which part is it so I don't have to replace everything?

 

David,
My personal tecnical knowledge is very limited so I`m afraid I probably be of no help in fixing your problem.
I personaly doubt that oil contamination is the problem - this was information passed to me by my regular garage, but as the tuner who fitted the kit indicated the sensors are usually reliable.
My problem was resolved by the tuner who fitted the MAF subsituting known working parts for my parts (I had the original barn door sensor refitted prior to returning to him)

 

Here is a completely different direction to look...

Directly in front of the engine at the base of the firewall is a 6 prong connector for the fuel injection harness. If it is loose it can do a lot of interesting things.

Make sure it is snug. Mine was floppy loose and none of the shops I had look at found it (over a 6 months period!). I wrapped a nylon tiestrap around it and it has been fine.

BTW - The only independent testing of the Autothority MAS that I have ever seen showed a 10 HP loss on the dyno! They didn't have an axe to grind but they just noted that the stock setup is very good.

 

David - where did you put the autothority 12 volt?
Also - any fueling changes? I had chip/maf problems before with autothority (my fault) - are you sure you have the correct number chip and good install.If you turn the fuel up enough, a maf car will run with stock chips (very poorly).

 

Hi all,
I was chasing a doggy idle on my 87 Carrera and the latest condition is an idle that cycles between 1000 and 1200 or so about once per second. I swapped out the idle speed regulator with another and there was no difference in the idle. Then I checked that the throttle was closed against the stop screw and that was fine. Then I verified thet the idle position switch was switching at closed throttle and off closed and that was ok.
Then I got tired of trouble shooting and plugged the hose to the idle positioner.
The cycling idle has now gone away. Idle is about 500rpm after starting and is steady at 900 when the engine is hot.
One other piece of data is that when on the road and giving it gas from a closed throttle condition, it seemed to get too much gas and was not smooth just then. With the hose corked, transition is perfect.
Having said all this, next up is to verify the signal to the idle speed controller with the throttle closed. The jerkiness I got when coming on throttle may be an indication thet the idle position switch mode is not being transmittted to the computer as this switch, off idle, controls fuel shutoff with a closed throttle when the revs are greater than 1300. No fuel cut off might explain the jerk.
Will post progress on Friday.
Ned Monaghan