MFI Running Too Cold

Jandrews · 01:31 PM

Hello,

I did a bunch of search attempts on this, as I know this has come up before, but I was unable to find a good discussion that is specific to this issue.

Here is the scenario. Completely rebuilt from the case out, '73 2.7 RS Spec motor with MFI. MFI Pump completely rebuilt and injectors flow-tested by Gus at Pacific. Proper "S" electric fuel pump. Fuel tank boiled and sealed. All new rubber fuel hoses. Volume tested fuel flow at 1,000 cc's in 30 seconds. Brand new RS distributor, plug wires and points. Tested NGK B8-ES, B7-ES, B6-ES (current), and Bosch W3DP0 plugs, and also have B5-ES. All MFI plumbing is in place and new, including the double warm-up hose to the thermostat, and both heater hoses from the exchanger to the fan ducts. Air filter is new. Ignition timing is set at 35 BTDC @ 6,000 rpms. Points gapped at .014", and then verified with a dwell meter at 38 degrees. Mocal external oil cooler.

I cannot get the operating temperature above 160, and it typically runs around 150. This is even the case on 60 degree days. I have tested (and kept track of) up to 4 clicks leaner (clockwise) on the main rack of the MFI pump to note any change with no success.

I am just reaching out for other ideas here on what I might look for. The MFI warmup thermostat is pristine and the discs untouched since Gus had it. I am not noticing any oil dilution from gasoline, nor any fuel in my breather catch can, and there is no strong fuel smell around the car.

Any ideas would be greatly appreciated.

Thanks,

JA

Grady Clay · 03-19-2006, 01:24 PM

John,

As always the first suspect is the MFI pump thermostat. Put a thermometer in the air exhaust of the thermostat and confirm it gets hot (180F). You can check to see if the thermostat is completely turning off by attempting to lightly push down on the thermostat bell-crank pivot in the MFI pump (little access plate on top of the pump). If lightly pushing it changes the mixture (running) then the thermostat is not off. You can use a heat gun or hair dryer to force the thermostat off.

Since you are evaluating this with oil temperature there are another two things to consider. First is the calibration of your oil temperature gauge. Next is the functioning of the oil thermostat(s).

The most critical issue is the exhaust gas mixture. If that is proper soon enough, then the other issues are less important.

Best,
Grady

Jandrews · 03-19-2006, 01:29 PM

Agree Grady...sure sounds related to the thermostat leaning function. I'll try your external tests and post back what I find!

As always, thanks,

JA

Jandrews · 03-19-2006, 06:46 PM

Grady,

I have not done any testing yet, but if I wanted to try the hair dryer / heat gun test, where would I aim the heat? In the thermostat exhaust? Or, should I remove the warm-up hose from the heat exchanger and aim the heat gun in the thermostat warm-air inlet?

Many thanks,

JA

Jim Richards · 03-20-2006, 03:47 AM

I'm confused (so what's new?)...what's the problem? The engine temp doesn't exceed 160? And no gas getting into the oil (so MFI's not too rich)? It's 60 degree or less when you drive it? What kind of revs are you running, and for how long?

Jandrews · 03-20-2006, 05:23 AM

Jim,

Yes, the issue is that I can't really get the motor up to operating temp. I don't believe it is advised to run the car hard when below operating temp, i.e. 160 or so. I can drive for hours and the temperature will typically not go above 150 degrees. I believe that is a problem, and not normal. I'm not sure I can conclude that the MFI is not too rich, just because it doesn't appear to be diluting the oil. I will try Grady's test to ensure the thermostat is turning off completely. We are supposed to get a foot of snow here in Kansas City today, so it may be a few days before I can really do any testing, but I would love to hear any other thoughts you might have.

Thanks,

JA

304065 · 03-20-2006, 05:33 AM

John, with a low OAT it's hard to get it to run hot in the first place. For example, I was driving my carbed 2.0 this weekend, it usually runs around 250 (too hot, I know) but I was seeing temperatures in the 200 range with a 33 degree OAT.

Certainly heed Grady's advice to the letter, make sure the system is working properly, but don't discount low air temperature, particularly if your testing wasn't done at high power levels e.g. continuous highway driving-- 50-90 "flexibility" testing.

Rot 911 · 03-20-2006, 05:34 AM

I am as confused as Jim. Why do you immediately suspect the MFI running too rich as a cause for the inability to warm up the engine. I would be more inclined to suspect either an oil thermostat being stuck open or your temperature sending unit being inaccurate.

Jandrews · 05:50 AM

Well, I am not necessarily assuming that this is fuel-mixture related. It could indeed be thermostat or gauge/sender related. I have a hunch that it is fuel/combustion related however. I was getting significant soot on a B7-ES plug, so now I am running B6-ES. I thought I would go one notch hotter and see what happens. I have not pulled a plug yet to take a look. Also, power is very good, but probably not 100%. I also need to check correlation on my MFI linkage. I was hoping Zeke would get the protractors built and I was going to pick up a set from him. So, I am not making any assumptions at this point, but I want to check the basic important things first, i.e. richness condition, and then I can easily deal with guages or thermostats.

Thanks for your thoughts.

JA

Jandrews · 03-20-2006, 05:47 AM

Oh, and John C,

Yes, OAT is obviously very significant on these cars. Regarding RPM range, I have done it all. I spent a whole day at the track with this car, flogging it pretty hard, and it still only "peaked" at 160. This was with OAT around 60 degrees. I hated the idea of running the car hard at that temp, but it just would not get hot, and you know what happens when you set foot on a track - you've just gotta run it.

I wish I had a really hot (OAT) to test it, but still, it seems like I should at least get 180, regardless of OAT, no?

Thanks,

JA

David E. Clark · 03-20-2006, 06:21 AM

Interesting dilemma. I’m not convinced that this is an MFI problem. At its most basic level, the engine is cooled by air and oil flow. Unless air and oil are adequately flowing, the engine is going to run hot -- the harder you push it the hotter it will get. The better the air and oil flow the cooler then engine will run. This has very little to do with the fuel mixture, although a rich running MFI system tends to run hotter and one so rich that there is oil dilution will run even hotter due to the inability of the diluted oil to cool as well as non-diluted oil. Since you haven’t noticed the car running rich (which in my opinion is more likely to cause the opposite (hot) condition) I would look elsewhere for the cause. For example, have you installed a supplemental oil cooler(s)? If so is it operating correctly? Is the outside air temp so cool that a longer “warm-up” is necessary? Is the oil temperature gauge/sender operating properly? Grady is Yoda when it comes to MFI so definitely follow his recommendations but don’t neglect to look elsewhere also.

304065 · 03-20-2006, 06:37 AM

John,

OK, check the temperature sender, it's probably gone south.

IF the engine thermostat failed closed, engine temp would spike off the chart.

IF the external thermostat failed close, ditto.

IF either failed open, the temperature would eventually get past 160 if you drove for an entire session on the racetrack.

Warren posted the resistance values vs. temperature for a working sender. oil temp sensor check?

Rot 911 · 03-20-2006, 06:42 AM

John I would never, ever run hotter than the BPR6ES in your car. I can't believe you ran it on the track and it never got hotter than 160. I am now suspecting more than ever you have a faulty temp. sender or gauge.

As an aside, I am going to be in KC the weekend of April 1, at the Imagine Auto open house with the KC Wrenching Society guys. You going to be around? I will be driving the 911 in from Lohman.

Jandrews · 03-20-2006, 08:11 AM

John C,

That's what I was thinking. Even if the external oil thermostat failed in the open position, it seems I would get higher than 150 degree oil temps on a 60 degree (OAT) day.

Kurt, I agree, I think B7-ES is a good plug for cooler seasons, but I like B8-ES for track/summer driving. B6-ES was an experiment, and it did not change anything. Anything hotter would likely cause detonation, so I would not go there. Based on your suggestion, I will do some more digging into the temp sender / gauge area. Glad you are coming to the IA event. I will try to be there as well and would like to meet you in person.

Thanks,

JA

Grady Clay · 03-21-2006, 12:00 PM

John,

I agree with the above. This is where an IR temperature gauge tool is invaluable. This is useful for diagnosing this problem, measuring your thermostat body temperature, calibrating your temperature gauge, measuring tire and brake temperatures and more. They typically cost under $100 and are well worth it.

I searched Pelican Parts and couldn’t find it. I’ll bet it is there and I’m just lame at searching.

Best,
Grady

Jandrews · 03-21-2006, 01:25 PM

Thanks Grady and others. There is some good direction here. I do have an IR temperature gauge, and will give it a try. I need some weather to pass here in KC before I go at this, but I will keep you all posted.

As always, thanks.

JA