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I made a post on here a few months back trying to get my 89 5.0 in running condition and we got there, all it needed was a new ignition switch. I got a rebuilt ECU out of that thanks to my troubleshooting. Anyways, now that it actually will start, it seems to not like to run cold. This morning, I tried to start it and it only turned over repeatedly. I got tired of that and swapped in a HUG2 ECU from a late model 5.0 f150 that we had for troubleshooting, and it fires right up. Granted it doesn't run extremely smooth, but its a lot better than what it does when I plug the A9L back into it. I let it get warmed up to 130 with the HUG2 installed, then I swap the A9L back in. Now when I start it, it has a terrible idle, like a serious vacuum leak; however, when it warms up to about 180, something literally clicks and then it idles and runs perfectly. Heres a link to a video of it doing it
. The grinding noise comes from the passenger side near the front. My speculation is that the solenoids for the smog pump air bypass and the EGR regulator turn on all of a sudden, thus hearing air escape from the bypass and opening the EGR valve, but I lack knowledge on how that whole vacuum system operates. With it running decently with an f150 ECU and terrible until something has to physically shift with the stock rebuilt ECU, I have a feeling it has to be the rebuilt ECU. It has a lifetime warranty also. I'm open to any suggestions. Thanks.
 

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I forgot to mention that the check engine light is on while it idles rough and goes out simultaneously when it smooths out.
 

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i tried, but the check engine light never flashes. Yes, I know which contacts to wire together. The contacts might be corroded because they are a little dull looking.
 

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You can always hook up a 12v test light to the self test output and check them that way.
 

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Discussion Starter #6
would you look at that...i stumbled upon a fuel line from the tank that had gotten moved somehow and is now burnt completely on one side due to it touching the exhaust. I will report back after that is repaired.
 

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Hey apex2624. Did fixing the line solve the problem? I have a 89 GT that does the same thing. When you crank it, it idles like it has a full race cam, then after about 2 minutes its like someone threw a switch and it idles great and runs fine. I have check codes, swapped out the ECM with a known good one. But have not solved the problem. Was interested if you fixed yours.
 

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Hey apex2624. Did fixing the line solve the problem? I have a 89 GT that does the same thing. When you crank it, it idles like it has a full race cam, then after about 2 minutes its like someone threw a switch and it idles great and runs fine. I have check codes, swapped out the ECM with a known good one. But have not solved the problem. Was interested if you fixed yours.
I fixed the fuel line but that didn't fix the rough idle. I replaced the ecu and that fixed it.
 

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Try cleaning the idle air control valve with some WD-40. I had an 88 LX that would lope like it had a race cam until it warmed up when the IAC would get dirty. Cleaning it fixed it every time.
 

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yea I have tried all the tricks. Changed ECT sensor, Checked the TPS, Checked the O2 sensors. check and clean the mass air sensor, checked the fuel pressure, Etc, Etc. Mine cranks better when it cold, the colder the better that's why I changed the ECT sensor thinking it had to do with the temp. Once you crank it and let it go through the rough idle to clear up, you can turn it off and back on it goes through the same 2 minutes of rough idle again and then clears up and idles smooth.
 
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