FBS Posted February 13, 2023 Report Share Posted February 13, 2023 (edited) I need some help trying to understand what is going on here.. I have this problem with what appears the car not getting enough fuel to idle and the mixture being to lean. I mentioned this in another thread but it was confusing so I will try again here. When you try to start the car when it is cold... it will start but not idle... I have to keep my foot gently pulsing on the gas to keep it going until its warm. once its warm it hangs out around 1500rpm. The only way it will idle is if the wires that normally go to the temp sensor that tells computer what the engine coolant temp is are hooked up to a separate Temporary temp sensor mounted up in front of the radiator which is constantly sending message to computer that its cool and therefore richen the mixture. If I hook it up to the one on the engine it wont idle. I have replaced the following parts Fuel Pump, Fuel Pressure Regulator, Distrubutor Vacuum unit, I took off the connectors on the injectors and cleaned them.. they looked ok anyhow but just trying to rule out any possibilities. l checked the output of the MPS... it was .91Volts. I had my wife turn off the key and turn it back on... it went to 1.45 volts... and then after 15 seconds back to .91volts... I did this 3 or 4 times and it was consistent. I can hear the little motor working so it seems fine. I checked the output of the TPS.. and adjusted fully counter clock wise its at 4.74 volts. I could not get any more . I have a spare TPS and checked it with that one and got the same voltage. When depressing the throttle... drops down to just over a volt and then back to 4.74 volts after releasing it. I tried the TPS/ISC procedure linked below both parts. The second method it does not say what screw to adjust but I assume its the ISC screw since in the factory manual its what is adjusted. When the wires to the Temp Sensor are plugged into the sensor on the engine no matter how much I tightened the ISC screw it never changed the engine rpm. As soon as I plugged it in to the one the is located in front of the radiator that is temporary the engine rpm increased dramatically and I loosened it to drop rpms. From what I can tell something is telling the engine to make the fuel mixture leaner... when it should not be..... I checked the Ohm's on the temp sensor on the block and it is the same as the temporary one in front of the radiator. What else controls the idle mixture or fuel mixture. My dad told me that he at one point he checked the plugs and they looked like the engine was running to lean... thats why he moved the temp sensor into some cooler air. I notice when I park the car after I drive it and the warm air get to the sensor up front when I go to start the car the rpms are down around 1000. I thought about checking the primary injector... maybe its clogged some.. but the car runs fine down the road... so that does not make sense maybe? The last thing that came to me was the O2 sensor.. maybe its telling the computer that mixture is to rich because something is wrong with it. I have not checked its output yet... thats next... What about the MAF... telling computer not enough air... lean out the mixture ? I have not checked that output yet. Does anyone have any ideas... or something I have overlooked... ????? Thanks FB https://www.starquestclub.com/forum/index.php?/forums/topic/28069-tpsisc-reset-87-89/ Edited February 13, 2023 by FBS Link to comment Share on other sites More sharing options...
TexasQuest Posted February 13, 2023 Report Share Posted February 13, 2023 Have you tested the coolant temp sensor for the ecu that's on the intake manifold? Link to comment Share on other sites More sharing options...
admin_JAinsworth Posted February 13, 2023 Report Share Posted February 13, 2023 I noticed you said the TPS is 4.74 volts and won't go to 5 volts. It should be .5 (point 5) not 5.0 volts. Have you checked the resistance of the CTS ( coolant temperature sensor)? The resistance check procedures can be found in the FSM on page 14-64 which is the fuel system section. Here is a link to an online manual for the fuel system: http://www.starquestgarage.com/manuals/service/conquest/1988/88_conquest_service_manual_-_group_14_-_fuel_system.pdf Jimmy 1 Link to comment Share on other sites More sharing options...
kev Posted February 13, 2023 Report Share Posted February 13, 2023 The three items to place attention to are the coolant temperature sensor (the two prong sensor that is vertical in the intake), the throttle position sensor, and the idle speed sensor. First off is to do as Jimmy said and measure the resistance of the CTS when the engine is good and warm. It should be around 300 ohms. Also, when the engine is hot, you can put a 300 ohm resistor between the two leads of the CTS connector and this will tell the ECU that the engine is warm. See if this changes anything. Now for the TPS/ISC/MPS. Your MPS seems to be working fine. As Jimmy said, the TPS should be .5V at idle and not 5V. It should sweep up to around 5V as you open the throttle plate. Adjust it to around .5V...doesn't need to be perfect yet. So once the car is nice and warm, turn it off and unplug the ISC servo connection (this is the second to last plug....the instructions on here are a bit confusing. You don't unplug the MPS connector which has the red, green, black wires, it is the one with the yellow-red, yellow-black, etc.) After unplugging, connect the yellow-red stripe wire to ground. Grounding this tells the computer the car is at idle even with the connector unplugged. Now fire her up. There are two idle screw adjustments on the injection mixer. The one that is easy to see and is vertical is the fixed SAS. The other is a bit harder to find (viewable from looking in from the passenger side of the car). The first thing I do is to unthread the fixed SAS screw several turns. This one is simply a safety so if the ISC doesn't do it's job, the throtte plate will close further until this is hit to prevent stalling. So you want that out of the way for now. Hopefully the car stays running at this point. Now turn the horizontal idle screw clockwise for increased rpm or counterclockwise for decreased. A timing light that reads rpm is beneficial to see your actual rpm but you can do it per the factory tack to. Turn the idle screw until you are at around 900rpms. The car should be idling really good at this stage. If not, there is a problem with the ISC or the TPS. Now turn in the fixed SAS slowly until you hear the idle just starting to increase. At that touch-point, the manual says to back it off one full turn. I actually like to back it about a half of a turn, sometimes even less. This lessens the effect of if and when the ISC doesn't do its job, the idle won't drop dramatically and stall the car. But you don't want the fixed SAS binding up with the idle screw, remember it is just a safety. You can then turn off the car. Put the key to on and now go back to your TPS and tune it into .5V at idle. Sweep your throttle plate from closed to fully open, you should see the voltage rising linearly. If you have an old analog volt gauge, it really helps to see if there are dead spots in your TPS. A more modern day digital unit sometimes misses this. Now plug it all in and fine up the car. Hopefully it is running good now and the problem is resolved. Kevin Link to comment Share on other sites More sharing options...
FBS Posted February 14, 2023 Author Report Share Posted February 14, 2023 (edited) Thank you for both of these replies Jimmy Texas Quest and Kev so appreciate your taking time to respond. I took the CTS that was out in front of the radiator and did the test in the manual with a thermometer and meter. It checked out perfect. I took the one out of the manifold and installed the one I checked. I have not checked the one I removed yet, but I know now I have one that is correct and working in the car. I tried starting the car... same issues with not rich enough mixture. When I was checking the fuel pressure regulator I did something to see if I was having issues with the valve that regulates the pressure. I put a pair of vise grips on the return to tank line... The instant I did this the engine rpm picked up and smoothed out like when you have a high idle car warming up scenario. Release the pliers... back to same issue. I took this as that I increased the pressure a bit and was getting more output from the injectors... Not a fix and not sure what I may damage if I do that but it told me what I think was happening in the engine. ( I did this after I installed the new pressure regulator.) What about the air temp sensor in the MAF... On a side note I was able to find a ECI checker MD998541.... and amazingly the proper harness... MD998452 ( which I had looked for a couple of weeks ago on ebay but no luck.) I checked yesterday and by golly it was there... $15.00... Checker was $75.00... The checker looks in good shape as well as the harness. If this thing works it might make this process easier.... it was worth a try. I will let you know what happens.... Edited February 15, 2023 by FBS Link to comment Share on other sites More sharing options...
admin_JAinsworth Posted February 15, 2023 Report Share Posted February 15, 2023 19 hours ago, FBS said: Thank you for both of these replies Jimmy Texas Quest and Kev so appreciate your taking time to respond. I took the CTS that was out in front of the radiator and did the test in the manual with a thermometer and meter. It checked out perfect. I took the one out of the manifold and installed the one I checked. I have not checked the one I removed yet, but I know now I have one that is correct and working in the car. I tried starting the car... same issues with not rich enough mixture. When I was checking the fuel pressure regulator I did something to see if I was having issues with the valve that regulates the pressure. I put a pair of vise grips on the return to tank line... The instant I did this the engine rpm picked up and smoothed out like when you have a high idle car warming up scenario. Release the pliers... back to same issue. I took this as that I increased the pressure a bit and was getting more output from the injectors... Not a fix and not sure what I may damage if I do that but it told me what I think was happening in the engine. ( I did this after I installed the new pressure regulator.) What about the air temp sensor in the MAF... On a side note I was able to find a ECI checker MD998541.... and amazingly the proper harness... MD998452 ( which I had looked for a couple of weeks ago on ebay but no luck.) I checked yesterday and by golly it was there... $15.00... Checker was $75.00... The checker looks in good shape as well as the harness. If this thing works it might make this process easier.... it was worth a try. I will let you know what happens.... Do you have a fuel pressure gauge you can use to check the fuel pressure with? Idle should be around 38 psi iirc and increase one pound per pound of boost. When you pinched the line the pressure should surge and increase significantly. On the CTS, does it have the original connector or has it been replace with two individual ones? The original is fool proof and can only be connected one way. If it has been replaced with two separate connectors, hooking them up on the opposite prongs will cause it to not work properly. Jimmy Link to comment Share on other sites More sharing options...
kev Posted February 15, 2023 Report Share Posted February 15, 2023 I'm still confused by what you mention as in front of the radiator. There are two sensors on the radiator itself but those are for the electric fans. On the intake, there are three temperature sensors. The CTS for the ECU is the one mounted vertically in the manifold and is the only one with two prongs on an 87. The larger one wire sensor is for the temperture gauge in the dash. The smaller one is a temperature switch associated with the air conditioning. Also, if you are squeezing the return fuel line and notice any changes, then you aren't getting the right fuel pressure...i.e. your FPR is bad. With a properly functioning FPR, you could squeeze all you want and not have any noticeable change in how the car is idling. Link to comment Share on other sites More sharing options...
FBS Posted February 15, 2023 Author Report Share Posted February 15, 2023 (edited) HI Kev, Jimmy Ok I get your confusion.... Some time back my father changed out the head and cam and put in a high performance cam and when he put it back together he had the problem I have now. In a different thread here I mentioned this. Someone said the cam would not cause the problem I have. So in an effort to solve it he connected a couple of wires to the connector for the CTS and extended it to mount it in front of the radiator in the grill of the car in the cool air stream. I know its not correct but thats what he did. I got the car and now I am trying to remedy these problems so it runs correctly. He discovered that when he did this the car would idle and have a richer mixture because he was fooling the ECU. I dont know what to say about what the fuel pressure regulator... Its brand new..out of the box... Car runs fine down the road and plenty of power ect... so I dont know why it would not have enough fuel pressure to idle.... I had borrowed a fuel pressure checker from Autozone... and somehow it actually failed while I was using it.. It was hooked up where the fuel filter outlet banjo bolt goes, so I never checked it after that. ( this was on the old fuel pump that I was checking the pressure, I never checked it on the new pump..no reason to. The reason why I replaced the fuel pump was I was having other problems not the same as these, those problems no longer exist..( car now starts, correct acceleration under a load, no sputtering ect. ) The connector to the CTS is the original one. I put in a brand new fuel pump too... so no ideas on this. I also checked and replaced all the filters between the tank and the throttle body including the little tiny one before the fuel pump in the hose. It has had this problem ever since he replaced the cam and the head. I dont know what he did when he took it apart... BTW my father took excellent care of this car... like to the point of writing down every last detail of the parts he changed ect in the owners manual. He changed the oil religiously.. followed all the factory suggestions. He did lots of work on the car to keep it in the condition it is in today. The interior is like new... My goal is to just get it back to running correctly. I may put the original cam back in but I wanted to see if I could remedy this problem without doing that first.. I apologize if what I write is sometimes confusing... doing the best I can.. with what I know... my knowledge on this car is minimum. No experience on computer driven fuel injection... my other car is a 1989 Mazda B2200...non fuel injected, which I am in the middle of trying to remedy a problem with burning oil like crazy after I changed out the head and put a new head on...like new compression and power so I am confused.. I got my hands full. Appreciate all you here, really I do... I have no car friends... you know guys to call to come over and help me so all your help is really appreciated... more than you know. Thanks Edited February 15, 2023 by FBS Link to comment Share on other sites More sharing options...
FBS Posted February 19, 2023 Author Report Share Posted February 19, 2023 (edited) On 2/13/2023 at 3:10 AM, admin_JAinsworth said: I noticed you said the TPS is 4.74 volts and won't go to 5 volts. It should be .5 (point 5) not 5.0 volts. Have you checked the resistance of the CTS ( coolant temperature sensor)? The resistance check procedures can be found in the FSM on page 14-64 which is the fuel system section. Here is a link to an online manual for the fuel system: http://www.starquestgarage.com/manuals/service/conquest/1988/88_conquest_service_manual_-_group_14_-_fuel_system.pdf Jimmy Ok... so I have to share my gratitude for Jimmy here... He unknowingly did me a HUGE favor. He posted this link to the Conquest Service Manual... The ECI Checker and Harness numbers are different in this manual than in the one I own for the 87 Starion. When I originally searched for those parts I used the ones in my manual and was not able to find the Harness because it had a different number. Jimmy had posted this so I download it on my computer. Last week when it came to me to take another look for those tools again I looked at the PDF Conquest version. First try on Ebay I found both... At the time I did not realize they were different numbers but are the exact same tools. I purchased them and only when I received them I checked them against the parts in the Starion manual... and got a rush of OH CRAP I ordered the wrong thing... after a short consultation with Texas Quest and my own digging.. I know they are the same tools, just different numbers... So Jimmy thank you for doing what you did and sharing that PDF with me.... otherwise I never would have found the ECI Checker and the correct harness... like the one in million... Some day I plan on changing out that system but until then I have something now to help me out that corresponds with the the procedures in the manual.... He won the day for me... Edited February 19, 2023 by FBS Link to comment Share on other sites More sharing options...
FBS Posted February 21, 2023 Author Report Share Posted February 21, 2023 (edited) Ok.. so I hooked up the ECI checker to the system and it worked perfectly. I was able to read all the components in the system that I can read. I discovered a couple of things that may be a problem but I am not sure about it. It picked up that the Air Temp Sensor was sitting at almost 5 volts when it should have been about half that. I did a Ohm resistance test on that sensor directly using a controlled temp heat gun and a voltage test. The voltage test was strange. It would stay at 5 volts while I applied the heat gun temp at 170 Degrees and then suddenly jump to about .9 to 1. volt.. sometimes it would swing back and forth.. and when I removed the heat it took a couple minutes to change but it went strait to 5 volts after dropping slightly. The Ohm test seemed to show that it was closer to the correct specifications but not exactly. Its difficult to test it for the cold, all I could do was put it in a freezer for a few minutes and then take it out and read it. It was close to the correct value. The second thing that was off was the EGR Solenoid Valve voltage.... It was 0 the entire time.. nothing I did rpm wise changed it. The O2 sensor seemed off but when I replaced it with a new one I got the same results and it states that the testing of that sensor is also subject to other things so it may not be accurate. I tried checking the Self Test which is that harness located behind the side of the glove box when you open it... I checked it in the correct way and I only got the standard battery type voltage showing no errors. This corresponds to what the ECI Checker also told me ...except that it did not say the Air Temp Sensor was bad... or had an error. It also showed no error for O2 sensor. I did manage to reset the TPS/ISC... The car idles at around 950rpm. TPS is at .5volts... MPS... is .9 volts. So.. the car still does not run correctly.. meaning this. While pushing foot down on the accelerator pedal I can push it down slowly and the engine does not change until I get it down far enough. In that in between space there is a little what feels like a sputter... and then suddenly... the engine rpms pick up and catch up. It seems like the TPS is not telling the computer what its doing... thats my guess. but when I checked it on the Checker.... I watched it at .5 volts.. and then when I put my foot down it went to 4.5 volts.... Hmmm as I am writing this I realized I did not check and see if it was a smooth transition from .5 to 4.5 Maybe its not working correctly. The car seems jerky when driving down the road....when your foot is not accelerating ..... I have not tried to see how it starts when cold yet... tomorrow, but it did run with the Temp sensor hooked up correctly. I used the reset procedure that is on this forum... When I connected the temp sensor back to the sensor that is mounted up front of the radiator This is a jury rigged sensor.) the problem stops.. because its cooler and getting a different signal to the computer telling it to send more fuel. Lastly as I stated once before that my father installed a Cam in this when he replaced the head and put a non jet head on it. He said after he did this it never ran correctly any more. He also replaced the injectors that look like they are from MotoCam.... but I am not sure. I know this one mechanic that told me that when people put cam's in cars that do not have adjustable EMS they have problems. Maybe this is the cause of why it does not run right. I am curious what any of you might have to say about this Edited February 21, 2023 by FBS Link to comment Share on other sites More sharing options...
admin_JAinsworth Posted February 27, 2023 Report Share Posted February 27, 2023 Over time the TPS will develop a "flat spot" and no amount of adjusting will help. It sounds like yours has done this. It is hard to find a new OEM TPS but MKS motorsport offers an alternative that will work. https://mksmotorsport.com/?s=tps&post_type=product&dgwt_wcas=1 Jimmy Link to comment Share on other sites More sharing options...
FBS Posted February 27, 2023 Author Report Share Posted February 27, 2023 Thank you Jimmy.... much appreciated. I did not know that, I have 2 more TPS's to try out... I suppose if I have the same problem, Mike has a good solution though. I did go looking for alternatives and I found this... https://www.rockauto.com/en/catalog/mitsubishi,1987,van,2.4l+l4,1208371,fuel+&+air,throttle+position+sensor+(tps),5136 I wonder if anyone has investigated this.,... It looks identical except for the connector... and its for a 2.4Liter motor.. Fionnbharre Link to comment Share on other sites More sharing options...
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