ReneH Posted March 16, 2023 Author Share Posted March 16, 2023 Your posts won't be considered spam, so don't worry. On the throttle opening, I don't think there is a specified one. But it isn't an exact science. You need enough throttle opening so the IAC isn't running 100% duty cycle or the IAC may burn out and the ECU won't be able to control very well. On the other hand, if you have too much throttle opening and the IAC doesn't have to run at all then the ECU will be hampered on that end as well. So if I were you I'd get things working pretty well and then start playing with throttle opening. I'd use my DVM to infer duty cycle on the IAC since if you see battery voltage when on the DC scale you know you have 100% duty cycle, and zero voltage means you have 0% duty cycle. And I'd shoot for something in the 30 - 40% range. OK. Good to know, Gary So, I think it's not good to start at too many places. So I will wait for the resistors and give the EEC at first the needed values for the emission control back. As far as I understand the EGR also supplies the throttle body with air while engine is warming up. So maybe this part of air is currently missing. If the ECU thinks the EGR is open, it won't open the IAC so much...so, that's my theory...will be interesting to see tomorrow if I'm right with it. Link to comment Share on other sites More sharing options...
Rembrant Posted March 16, 2023 Share Posted March 16, 2023 Another question: I use an IAC from a 1990th truck...for what the hell is this black plastic cap? Something for adjustment? Vent;). Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 16, 2023 Share Posted March 16, 2023 OK. Good to know, Gary So, I think it's not good to start at too many places. So I will wait for the resistors and give the EEC at first the needed values for the emission control back. As far as I understand the EGR also supplies the throttle body with air while engine is warming up. So maybe this part of air is currently missing. If the ECU thinks the EGR is open, it won't open the IAC so much...so, that's my theory...will be interesting to see tomorrow if I'm right with it. Right, you shouldn't be changing lots of things at the same time. But I think the ECU will keep increasing the duty cycle of the IAC until it gets the desired RPM - regardless of whether or not there is anything coming in via the EGR valve. BUT, if you have the throttle blades closed to the point that the IAC is already running at almost 100% then the ECU cannot get the RPM up. Link to comment Share on other sites More sharing options...
ReneH Posted March 16, 2023 Author Share Posted March 16, 2023 Another question: I use an IAC from a 1990th truck...for what the hell is this black plastic cap? Something for adjustment? Vent;). Hey, Thanks! I also thought about a vent...but I can't imagine that this will have any use there...but maybe it has. Thanks anyway. Now I know what it is! Link to comment Share on other sites More sharing options...
ReneH Posted March 16, 2023 Author Share Posted March 16, 2023 Right, you shouldn't be changing lots of things at the same time. But I think the ECU will keep increasing the duty cycle of the IAC until it gets the desired RPM - regardless of whether or not there is anything coming in via the EGR valve. BUT, if you have the throttle blades closed to the point that the IAC is already running at almost 100% then the ECU cannot get the RPM up. Ok...but if I assume this, there is something wrong with my idle screw or the counterplate. The engine only starts if I turn the screw completely in or pull a vacuum hose...I can't imagine that this only results in a combination of the throttle opening and the TPS signal... Ignition is set to 10 deg. BTDC without SPOUT connected...and it runs very raw...maybe I need to set the timing higher cause of my 351W cam and the stroker kit...one from FSB told about 12 degrees... Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 17, 2023 Share Posted March 17, 2023 Ok...but if I assume this, there is something wrong with my idle screw or the counterplate. The engine only starts if I turn the screw completely in or pull a vacuum hose...I can't imagine that this only results in a combination of the throttle opening and the TPS signal... Ignition is set to 10 deg. BTDC without SPOUT connected...and it runs very raw...maybe I need to set the timing higher cause of my 351W cam and the stroker kit...one from FSB told about 12 degrees... If I understand what you mean by "turn the screw completely in" you mean that you have to open the throttle as far as possible with the idle set screw in order to get it to run. That seems to say that the ECU is giving the engine too much gas. That might be due to the TPS voltage being high, causing the ECU to think the throttle is open farther than it is. How about adjusting the TPS so that the voltage comes down? Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 17, 2023 Share Posted March 17, 2023 If I understand what you mean by "turn the screw completely in" you mean that you have to open the throttle as far as possible with the idle set screw in order to get it to run. That seems to say that the ECU is giving the engine too much gas. That might be due to the TPS voltage being high, causing the ECU to think the throttle is open farther than it is. How about adjusting the TPS so that the voltage comes down? One item I ended up doing on my son's 1986 F150 302 was to drill two small holes in the throttle plates. The 351 throttle body may have them in there anyway. Since you probably have more access to metric drill sizes, I would start with 2.0mm and if you can't get a reasonable idle at 1.0V, then go up in small increments until you can get a decent idle. Once you get there, go one step further so the IAC is controlling your idle, otherwise it will not be able to raise the rpm on cold starts or in gear. TPS, is not really adjustable on these, nor easy do to it's location on the bottom of the throttle body. Link to comment Share on other sites More sharing options...
ReneH Posted March 17, 2023 Author Share Posted March 17, 2023 If I understand what you mean by "turn the screw completely in" you mean that you have to open the throttle as far as possible with the idle set screw in order to get it to run. That seems to say that the ECU is giving the engine too much gas. That might be due to the TPS voltage being high, causing the ECU to think the throttle is open farther than it is. How about adjusting the TPS so that the voltage comes down? Yes, you've understood what I mean. I also have tried to press the pedal to the floor and crank the engine to sweep out the cylinders, but there was no cutoff of the injection...the engine starts... I have read in this book about the EEC that this should work... But if you have seen, my TPS seems to be inside the range... Link to comment Share on other sites More sharing options...
ReneH Posted March 17, 2023 Author Share Posted March 17, 2023 One item I ended up doing on my son's 1986 F150 302 was to drill two small holes in the throttle plates. The 351 throttle body may have them in there anyway. Since you probably have more access to metric drill sizes, I would start with 2.0mm and if you can't get a reasonable idle at 1.0V, then go up in small increments until you can get a decent idle. Once you get there, go one step further so the IAC is controlling your idle, otherwise it will not be able to raise the rpm on cold starts or in gear. TPS, is not really adjustable on these, nor easy do to it's location on the bottom of the throttle body. Hi Bill, Ok, this sounds like a plan. I have bought three different TPS last year and check which of them was as close as possible in the voltage range, combined with my throttle body. It also has a little larger holes, so I'm able to adjust a bit. So I will start with your manual and see if I can start the engine. I also will measure if the IAC, if it gets 100% duty-cycle in warming up/idling... Link to comment Share on other sites More sharing options...
mat in tn Posted March 18, 2023 Share Posted March 18, 2023 One item I ended up doing on my son's 1986 F150 302 was to drill two small holes in the throttle plates. The 351 throttle body may have them in there anyway. Since you probably have more access to metric drill sizes, I would start with 2.0mm and if you can't get a reasonable idle at 1.0V, then go up in small increments until you can get a decent idle. Once you get there, go one step further so the IAC is controlling your idle, otherwise it will not be able to raise the rpm on cold starts or in gear. TPS, is not really adjustable on these, nor easy do to it's location on the bottom of the throttle body. I do wonder how much we are getting "wires crossed" so to speak. not certain that whether the throttle body itself is from a 5.8 or 5.0. by turning the base idle throttle screw all the way in you are not only allowing more air but rotating the tps also putting it well into the operating range of adding fuel. much as you would by stepping on the pedal. however, by removing a vacuum cap or hose you are not. this tells me that you may be dealing with either a map failure or you may have an injector not sealing shut when told to do so. does the system hold static pressure while turned off and for how long? Link to comment Share on other sites More sharing options...
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