Head scratcher
05-16-2019, 10:18 AM
#1
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Head scratcher
I have been dealing with this problem for a long time, hope someone can help. 95,302, all stock.9 times out of 10 will start and run perfect then when started runs rough to very rough. Runs maybe a minute then smooths out, might not stop for a few miles. Vacuum is at 19 inches when running well, I have checked when running rough and it is 5 to 6 inches. This condition will stop as quick as it starts. I have changed all vacuum hoses, pcm, fuel pump, pressure reg, checked cts, tps, iac fuel pressure, all good.I have sprayed carb fluid everywhere trying to find vacuum leak. Sitting still at idle running smooth I can rev engine hard and when returns to idle it will be running rough and gets worse each time I rev it. I hope someone can shed some light on this mystery to me. Thank you
05-16-2019, 08:11 PM
#2
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Did you check fuel pressure when the engine was stumbling? You might hang a gauge and situate it where you can monitor it as you drive and hopefully get it to act up. I do not think you have a vacuum leak.The engine will race with a bad leak. The 5-6 inches is a symptom of the poorly running engine.An EGR valve which may be hanging open comes to mind. Pull and plug the vacuum line to it and see if it behaves the same.
Last edited by raski; 05-16-2019 at 08:14 PM.
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05-17-2019, 10:27 AM
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Checked this morning. First I took a mirror and watched to see if it was actuating when eng revved. It was working but I removed and cleaned and made sure the pintle was free. I went ahead and changed it with my 94 f150 that runs fine. No difference in either truck. I did notice that when I revved the engine 3 or 4 times to make it run bad the fuel pressure went from 32 at idle to 39 at idle and stayed there.It also has never thrown any codes when it acts up. Any ideas will be greatly appreciated. Thanks all
05-18-2019, 06:27 AM
#6
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Hang your gauge back on the fuel rail. Start her up, confirm you have 30-45 psi at idle. Pull the vacuum line off the regulator, pressure should go up. Goose the throttle, if pressure briefly drops drastically then goes up would indicate a weak fuel pump. I still believe your EGR may have been hanging up.