Of Mice & MFI (not for the squeemish)

[mhackney]

I have been having high idle (1600RPM) problems with my 70 S for some time. I've been going throught the Check, Measure, Adjust process. Changed plugs, oil/filter, points, set dwell, checked and adjusted dizzy advance, air cleaner, gas filter, lubbed all the throttle ball joints, etc. Today I was starting to look in to the thermostat so after warming the car up, I pulled off the air house so I could check the air outlet on the thermostat. Nothing was blowing through! So I removed the corrugated hose from the thermostat (it was a new hose replaced when I pulled the engine 2 1/2 years ago. The car had been sitting for 2 1/2 years unused until just a few weeks ago). When I looked in the hose, here is what I saw:



Upon gently pushing it out:



I removed the thermostat and its core (which seemed to be in good shape). I cleaned the housing to remove "mouse" and reassembled. Got everything back together. I still have the high idle speed but I am not experiencing the gurggling on fast decelleration and other symptoms I attributed to running rich.

However, I did discover that the throttle return spring (there is only 1 on the left side) was just floating free. The 90 degree bent end on the right side should engage a hole to keep spring tension. How much tension is supposed to be in this spring? and does the left side that hooksover the throttle arm hook over the top or bottom? If I pulled up very hard on the throttle the engine does slow down to a normal idle. Perhaps I have a simple mechanical problem couled with mouse-induced richness!

Cheers,
Michael

[kaisen]

Is that the opposite of a plugged cat?

[svandamme]

Originally posted by mhackney

However, I did discover that the throttle return spring (there is only 1 on the left side) was just floating free. The 90 degree bent end on the right side should engage a hole to keep spring tension. How much tension is supposed to be in this spring? and does the left side that hooksover the throttle arm hook over the top or bottom? If I pulled up very hard on the throttle the engine does slow down to a normal idle.

had the same thing on mine, the spring would pop out
i think that the environmental warm air gizmo had a bracket that bolted on top of the spring, and that kept it in place , perhaps Grady can comment on this

as for how much tension... dunno really, trial and error a bit till the return on the throttle rack is adequate, the pump itself also has a spring, both together work to return the rack to idle position

[mhackney]

Well, I am not convinced that the return spring is the issue. The throttle actually returns all the way to the stop. Once the idle RPMs are up around 1600 it doesn't really slow it down to pull the throttle back on the stop. However, if I am driving and put a little strain on the engine to lower the rpms, they go to 950 and stay there. The other thing I noticed and need to check out to understand how it works is the microswitch my not be doing anything. But I need to understand how it works before I can tell for sure. If you give the engine a little gas and hold it - say at 2000rpm, and then manually press the microswitch, shouldn't you see a drop in rpms? I see nothing happen.

cheers,
Michael

[svandamme]

the throttle stop switch controls the fuel shutoff solenoid
but is also controlled by an RPM relay, eg, the relay should only provide voltage if the RPM is above a certain rpm((if i remember correctly 3500 revs)

[svandamme]

what happens if you disconnect the pump, and both throttle bodies??? does it idle at high speed then as well?? or does it settle at a normal rpm?

[mhackney]

I know it stays high if I disconnect both throttle bodies. I'll disconnect the pump and try it now. Is the pump connection on the left side as you face forward?

Thanks,
Michael

[svandamme]

yep, on a golden/yellow lever, can't miss it

there's only 4 linkages on the control rack
1 to the pedals
1 to the pump
2 to the throttle bodies


it's not part of the usual troubleshooting, but i did this on mine, to make sure that all 3 went to the stops, TB's and pump

if this doesn't change the idle, then i think you'll have to dig a little deeper, with the Check Measure Adjust procedure, cause the Throttle bodies give to much air at idle setting

you'll find the technical articles on the following page

http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

[mhackney]

Stijn,
I was mistaken. I went out and gave your suggestion a try. Most certainly, the right throttle connection is about 1.5 mm too long. As soon as I removed it, the idle speed came down. It also seems that the MFI link is just slightly long - maybe .5mm or so. Disconnecting the MFI, in about 10 seconds, the idle speed came down to 950rpm.

I am using the MFI info in the tech area you linked too - all great stuff! I am encouraged that the right throttle was not fully closing. Any suggestions on how to adjust the throttle linkage? And should I worry about that extra .5mm on the MFI linkage?

regards,
Michael

[svandamme]

don't go messing with it too fast, read the CMA doc first, it's a complete MFI troubleshoot, wish i could explain it better myself, but i'm not analytical enough myself , you don't wanna know the crap i've done to my mine... 't was the school of hard knocks for me, attention span of a chipmunk

[mhackney]

Stijn, I have been working through the CMA from the very beginning. As I mentioned in the first post on this thread, I've slowly been chasing through everything. That is what led me to discover the mouse! Most certainly, discovering that the right throttle is not completely closing is the "best" problem I've discovered so far. I will proceed very carefully with the linkage adjustment. Only adjusting the right throttle a little bit and putting some miles on it.

cheers,
Michael

[svandamme]

sounds like a good plan, post an update if that works or not

[mhackney]

Made the adjustment and will be going out for a long drive in a few minutes! It is a beautiful evening here in New England. Clear, warm and dry.

cheers,
Michael

[mhackney]

OK! I was out driving for 3 30 minute stints and the idle speed drops down to 950-1000rpm consistently under all driving conditions! I've lived with this problem since I first got the car and I've had various people look at this problem off and on. I really did not have the S very long when the clutch fork pivot problem I had required me to pull the engine 2 1/2 years ago (see my other threads). Then I was unable to get the car to start after reinstalling the engine - until about a month ago. Since then, I've been systematically going through all of the systems and R&Ring them. Just finished all new fuel lines and next on the list is a brake fluid change and 4 SS brake lines.

Stijn, thanks for the help! Your suggestion led me to the solution. Even though I had removed the throttle linkages, I did it primarily to clean and grease the ball joints and was not paying attention to the engine per se. As they say, check the simple things first.

Cheers,
Michael

[Grady Clay]

Michael,

Looks like you have done your homework. Good for you. Finding the mouse and Sitjn’s good advice got you running well. Congratulations.

One CMA measurement is the temperature of the air coming out of the thermostat exit vent. That would have identified the mouse (or at least a problem getting heat to the thermostat) long ago.

A common issue when a thermostat has not been working correctly is the main mixture has been adjusted lean to compensate for the continuous rich from the thermostat. Now that the thermostat turns off, the system will be very lean. The symptoms are poor throttle response, surging, poor power and exhaust popping. This is a situation you need to look at.



OK, on to some of the issues raised.

There are actually eight return springs; one on each of the throttles, one at the lever on the MFI pump and one at the left side of the throttle cross shaft. Actually you might consider the accelerator pedal a ninth spring as it wants to return to the closed position.

When diagnosing this please don’t make any linkage adjustments. If needed, that comes later.

With it at idle; disconnect one end of every link to the individual throttles. How does it idle now? Are all the throttles on their stops? Reconnect everything at the throttles. Do any come off the stops?

With all the links off the individual throttles, now is the time to measure the air flow to each cylinder. What differences cylinder to cylinder and left to right.?

With it at idle, disconnect the links (one-at-a-time) to the L&R throttle bodies. If the idle changes, was the linkage holding the throttle open? With one linkage disconnected, push closed that throttle body. Any change? Repeat on each individual throttle. Any change in idle? Is each throttle still on the stop?

Probably one of the rods from the cross shaft to throttle body has the individual throttles on the stops and the other has them off the stops. Carefully adjust the link that wants to open the throttles. Be VERY careful to keep track of EXACTLY how much you adjust it (it may take multiple adjustments).

The goal here is to have each of the six throttles come off the stops at exactly the same time. Search Pelican on MFI and correlation and protractors.

The above is only a small part of the CMA2 correlation procedure. One thing you need to investigate is how well the throttles and idle settle. This is an indication of the degree of wear in the throttle bodies.

The goal here is to recover from the mouse attack and decide what is next. Included in that are the basic CMA Checks and Measurements;

Best,
Grady

[mhackney]

Hey thanks Grady - this sounds like a good bext project to go through everything. I do have an airflow meter and will check everthing. I also had ordered a thermometer http://www.amazon.com/gp/product/B00023RVQG/104-4125458-6194308 but it won't get here until next week. Too bad I didn't have it before! I also have Gastester so I can check the CO levels now that the idle is under control

In my case, the right throttle linkage was definately not allowing the throttles to close to the stops. A 1.5mm shortening of the linkage and now they definately do. I will check the flows and proceed as you advocate. I'm lucky in that I have Matt Blast from Eurometrix less than 3 miles from my house! Matt rebuilt the Solex's in my Roadster a few years ago so I know the miracles he can work!

Cheers and a big thanks for the help.

Michael

[Early_S_Man]

Michael,

Did you locate the rest of the mouse's family???

If not, I would suggest removing the alternator and fan to take a look above the cylinder fins ... ShopVac could come in handy!

[mhackney]

You never know with these things but I have initiated an all out offensive. I have a lift so I've looked under, over and in everyplace I can get to. Since I had to do a shift linkage adjust and refreshed all the lnkage bushings I was able to look in that area too.

I am pretty sure the nest was in a connecting shed/bay to the garage (I found one there). Last weekend I literally took everything out of the shed and garage, cleaned, reorginized and reassembled. I've caught 2 mice in traps in the last few weeks. I am keeping a trap in the engine compartments of both cars with the roadster up on the lift.

I'll double check the engine compartment as you suggest. I've wanted to do a little polishing on the fan and replace the belt so this might be a good time to do it.

I apparently have 2 flavors of mice. 1 type is your typical grey field mouse and the other is very dark grey with a white underbody. According to some googling, it appears to be a white footed mouse.

Cheers,
Michael

[mhackney]

You never know with these things but I have initiated an all out offensive. I have a lift so I've looked under, over and in everyplace I can get to. Since I had to do a shift linkage adjust and refreshed all the lnkage bushings I was able to look in that area too.

I am pretty sure the nest was in a connecting shed/bay to the garage (I found one there). Last weekend I literally took everything out of the shed and garage, cleaned, reorginized and reassembled. I've caught 2 mice in traps in the last few weeks. I am keeping a trap in the engine compartments of both cars with the roadster up on the lift.

I'll double check the engine compartment as you suggest. I've wanted to do a little polishing on the fan and replace the belt so this might be a good time to do it.

I apparently have 2 flavors of mice. 1 type is your typical grey field mouse and the other is very dark grey with a white underbody. According to some googling, it appears to be a white footed mouse.

Cheers,
Michael

[mhackney]

Ok, I started some of the process. Basically, at a 950rpm idle, I removed all of the throttle linkages and there was no change to idle. Reattched them and again no change. Throttles are all on their stops. While the linkages were off, I measured the following flows (STE SK flow meter):


Cyl Flow (KgH)
--- ----------
1 5.0
2 5.0
3 5.0
4 5.0
5 4.7
6 4.7


Of course, this is after I made the linkage adjust to the right throttle link yesterday.

Also, it is much hotter today and when I went out for gas and a little spirited drive I noticed that the engine is just a tad hotter than "normal" and the idle would only come down to 1200rpm or so. It looks like I still have some work to do.

Is a .3 Kg/H difference in flow on 5 and 6 significant?

What would you recommend as next steps? I think I should probably recheck the advance now, maybe before doing anything else.

cheers,
Michael