Need help as I am about to pull what hair I have left out. Truck is a 1985 F150 300 Inline 6. Offenhauser DP, Long tube headers, HEI Distributor, Summit Max-EFI 500 fuel injection system. This thing has been a royal PITA. Finally got it running pretty well but there is one major issue that makes it almost undriveable. Truck idles fine in park with about 18 in Hg, fairly smoothly with minimal vibration. The issue is I'm having is in gear at a stop. The transmission is a C-5 auto. Driving down the road it runs perfect but come to a stop light and once you stop, it take about 10 seconds and you can hear the IAC valve pissing off air. Vacuum goes from about 14 to about 12 as the IAC keeps dumping more and more air. This makes the truck start running rich and shaking all over the place. Put it in neutral and it smooths out and after a few seconds the IAC closes and stops hissing.

Besides tuning over and over to try to see if it is a setting in the computer, I have also tried. Changed the IAC valve. Only doing this in gear and at a stop I thought maybe something to do with the vacuum line going to the transmission, this is the transmission modulator I believe? Anyways, I chocked the vehicle and put it in drive, it takes about 15 seconds for the IAC to start letting off air and it running rough. I tried pinching different vacuum lines including the one going to the transmission in an attempt to see if it could be a situational vacuum leak but nothing changed. Also does not matter whether the brake is on due to me blocking the tires and just letting it idle, still did it.

Any help would be appreciated, I made the mistake of going with Summit's sole FI unit and am paying the price, zero customer support for it. It is basically a rebranded FiTech made for Summit, many things especially with the programming are the same, but the unit is different so you cannot use FiTech support. About to bite the $900 dollars and just spend $1200 on a Holley that will run right and has tech support.

 

There is tech support for the summit efi. Call the 1-800-230-3030 ask for me Rush. Extension 6654

it sounds like the iac valve is opening, and that’s why your hearing the vacuum noise. What kind of ignition system are you running? What is the iac numbers doing when it’s making the noise? Is the rpm changing on the handheld? Afr numbers?

 

Awesome! I will get the answer to the questions you asked tomorrow. The ignition is a Summit HEI.

 

Ok, these are the numbers at idle in park with no load on the engine.
IAC Steps: 12
IAC Learn: 10
IAC PID: -44
Target AFR: 13.48
AFR: 13.8
AFR Trim %: 0.0
AFR Learn %: -21.9

And here are the same fields with the truck in drive stopped and hearing the hissing IAC
IAC Steps: 55
IAC Learn: 9
IAC PID: 6
Target AFR: 13.54
AFR: 13.9
AFR Trim %: 0.0
AFR Learn %: -21.9

Do not see a change in RPM

 

I had a similar issue with both a FAST EFI system, and more recently a fitech. If i ever convert a vehicle to EFI again I’ll probably use Holley.

That being said, I was able to fix IAC whistling, and improve drivability, by calibrating the IAC. I don’t recall what exact steps i followed or where i found instructions on how to do it, but i read through the below link quick and it seems to hit on the important parts.

https://www.onallcylinders.com/2017/...ng-efi-system/

Also, is your timing correct? I think my vacuum advance is out of spec which could be causing me some odd issues. Lastly, make extra extra sure you don’t have any vac, intake, or exhaust leaks that will throw off your o2 and vac readings.

 

I checked a few times on the leaks and am pretty sure I have it all sealed up. I think the IAC cal might be part of it. I have reset to defaults 4 or 5 times and went through setup again and seems to happen regardless.

 

Yeah, I don't know why the basic instructions don't explain how to properly calibrate the iac. Resetting and letting it whistle just isn't enough.

 

What cam does this have?
iac number isn’t crazy high , maybe a little high. Have you put a timing light on it to see what the timing is doing when this happens?

if you would please data log a few minutes of idle and drive while is acting up, and email me the data log so I can see what it’s doing.. rush6654@summitracing.com

 

Thanks for your help Rush! And brkdncr. I messed with the idle and got the steps pretty consistent and it idles much better at a stop. I still need to finish playing with it but redid my A/C system this weekend. I have a summit HEI distributer Rush, when I set the timing I need to unplug the vacuum advance, correct? I set the timing and kinda left it alone once I got it running but I could prob check it again to make sure. I always seem to be tinkering with it and honestly just want to get it running smooth so I can enjoy it this summer. I changed the AC compressor, etc this weekend and took it for a drive and everything was fine until I hit the interstate. I kinda zoned out for a minute and looked down and my coolant temp was at 220. I put a 190 thermostat in it but I'm thinking with higher speeds/increased engine loads I need to get a 160. Also want to put a nice new radiator with electric fans but I have to control my spending, haha.

 

Hei should work fine with the efi. Your correct, timing should be set with vacuum advance unhooked and plugged. Then plugged into the vacuum port with the lower vacuum at idle. I have seen rpm’s and vacuum change some while there learning. Keep a eye on the afr/target afr. If it seems rich and it’s close to the target afr, then you can lean it out by changing the target afr at idle. Mechanical fan works great with a fan shroud, running hot at higher speeds isn’t a fan issue, its normally a coolant issue,(not enough radiator, plugged radiator, too much or too little water flow) or airflow. If the outside air temp is hot, it will run hotter. 190 thermostat running at 220 is not crazy hot, a better radiator would help that. What was the outside temperature? 90° on a asphalt road in the sun, the ambient temp of the air could be much hotter 130°? Then your cooling 190° coolant with 130° degree air. That would make it run hotter. You could try a 160° thermostat and see if it helps. I would probably use a 180°

also….what fuel pump (flow in gph) / regulator are you using? Do you have a fuel pressure gauge? What’s the pressure at idle? Too small of a return line could cause the fuel pressure to be high at idle and make it run rich.

 

Hi, yours is the only thread that I can find that seems to have the same issues that my max EFI has developed. Did yo get to the actual problem and find a cure.
Thank you in advance.
Malcolm