delco1946 Posted July 15 Share Posted July 15 My 81 F250 5.8M idles slightly rough - almost like its got a small vacuum leak. Sometimes it almost goes away, other times at a red light its more noticeable. I've given up trying to find out why. Mention this in case it is relevant... The issue i'm asking about is a really rough idle when the engine heats up. This could be idling in the costco gas line for 10 minutes, stop and go traffic on a 95 degree day, etc. Whenever my engine temps climb it starts idling so poorly I worry it might stall. A couple times it has (think idling in a 4 hour wait in line for compost - don't ask haha). The only way to cure it is to start moving again to drop the engine temps to (presumably) 195 which is my thermostat set point. Its also a heavy duty truck with matching radiator so even on a 100 degree day, if i'm moving it isn't reading any hotter then on a 40 degree day (as long as i'm moving). What could be the culprit? I have the carb set as lean as it will go when I register in February to pass emissions. I leave it there to maximize MPG. Is it simply too lean in the warm weather that gas starts to vaporize? The EGR is probably ~ 4 years old and always test fine. Link to comment Share on other sites More sharing options...
viven44 Posted July 15 Share Posted July 15 Going from easy to difficult --- Is EGR vacuum hook-up correct ? Should be tied to ported vacuum only. Sounds like EGR may potentially be on manifold vacuum. Of course, there's the vapor lock which is the more difficult one. Link to comment Share on other sites More sharing options...
delco1946 Posted July 15 Author Share Posted July 15 Going from easy to difficult --- Is EGR vacuum hook-up correct ? Should be tied to ported vacuum only. Sounds like EGR may potentially be on manifold vacuum. Of course, there's the vapor lock which is the more difficult one. I've checked that (and it doesn't run thaaaat rough normally when not too hot. Rougher than i'd like but nothing unreasonable). The primary issue only surfaces once the temp needle creeps up (but still not overheating/on the far right side). Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 15 Share Posted July 15 I've checked that (and it doesn't run thaaaat rough normally when not too hot. Rougher than i'd like but nothing unreasonable). The primary issue only surfaces once the temp needle creeps up (but still not overheating/on the far right side). Consider coil breakdown or the module overheating. Coolant passing through the engine 'should' eliminate too much variation, but underhood* temps will soar if the truck isn't moving. My phone is incredibly frustrating when it decides it knows better than me what I'm typing. 😖 Link to comment Share on other sites More sharing options...
delco1946 Posted July 16 Author Share Posted July 16 Consider coil breakdown or the module overheating. Coolant passing through the engine 'should' eliminate too much variation, but underhood* temps will soar if the truck isn't moving. My phone is incredibly frustrating when it decides it knows better than me what I'm typing. 😖 hmmmmm that's a good point/question. I don't recall ever replacing the coil. Distributor cap yes, but coil no. I'll take a look at it and any records I may have. Are there any tests you recommend to identify heat related breakdown? Otherwise i'll just google it. I've never really bothered with the module, i'm not ever sure what its role would be on my truck, it should be pre-computer stuff. Pre -EEE and other acronyms i've been able to ignore for years. Thanks! Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 16 Share Posted July 16 hmmmmm that's a good point/question. I don't recall ever replacing the coil. Distributor cap yes, but coil no. I'll take a look at it and any records I may have. Are there any tests you recommend to identify heat related breakdown? Otherwise i'll just google it. I've never really bothered with the module, i'm not ever sure what its role would be on my truck, it should be pre-computer stuff. Pre -EEE and other acronyms i've been able to ignore for years. Thanks! The module is basically just a transistor that's used to cut power to the coil and initiate spark. The ribbed aluminum case is a big heat sink. Ignition coils can work fine when cold and start to cut out when they get hot. This is why I suggest examining them for function, and why I keep "known good" spares,. As it's easier to swap one and see if the problem goes away than it is to set up a test where you can heat the component and put it under load.... Link to comment Share on other sites More sharing options...
delco1946 Posted July 22 Author Share Posted July 22 The module is basically just a transistor that's used to cut power to the coil and initiate spark. The ribbed aluminum case is a big heat sink. Ignition coils can work fine when cold and start to cut out when they get hot. This is why I suggest examining them for function, and why I keep "known good" spares,. As it's easier to swap one and see if the problem goes away than it is to set up a test where you can heat the component and put it under load.... I’ve ordered a motorcraft ignition module and a coil. The coil was clearly replaced at some point (it’s a yellow accel aftermarket version with matching wire). The module must be original. The wires and connectors that plug into the module look pretty rough/ corroded. Mine have lots of broken plastic and are taped closed. Lots of green corrosion on one wire. I didn’t see a replacement online, but I’ll post a picture - I’d be curious if anyone knows of replacements. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 22 Share Posted July 22 I’ve ordered a motorcraft ignition module and a coil. The coil was clearly replaced at some point (it’s a yellow accel aftermarket version with matching wire). The module must be original. The wires and connectors that plug into the module look pretty rough/ corroded. Mine have lots of broken plastic and are taped closed. Lots of green corrosion on one wire. I didn’t see a replacement online, but I’ll post a picture - I’d be curious if anyone knows of replacements. Painless offers a DS-II wiring harness 'kit' You can ignore the ballast and the retard wires These are already built into the truck. Vivek seems to have found a replacement for the elusive distributor connector, the other 2-3 are readily available. So $$$ for everything, and then some, or you can get creative and build your own. Link to comment Share on other sites More sharing options...
delco1946 Posted July 25 Author Share Posted July 25 Painless offers a DS-II wiring harness 'kit' You can ignore the ballast and the retard wires These are already built into the truck. Vivek seems to have found a replacement for the elusive distributor connector, the other 2-3 are readily available. So $$$ for everything, and then some, or you can get creative and build your own. Dumb question. I ordered a blue streak coil which supposedly is good quality. I'm so irritated with it though. What should have been a 15 job is still incomplete. normal coils, including my old one had threaded screws to connect the wires to. The new Blue Streak on just has these weird studs that I can't connect to. It came with no instructions, no help, and when I google this problem nothing pops up. Pretty annoyed at this point that i'm going to have to also change my wires now and also annoyed at being so put-out by what (apparently) everyone else knows about. ....so how do I connect to these brass terminals???? Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted July 25 Share Posted July 25 Dumb question. I ordered a blue streak coil which supposedly is good quality. I'm so irritated with it though. What should have been a 15 job is still incomplete. normal coils, including my old one had threaded screws to connect the wires to. The new Blue Streak on just has these weird studs that I can't connect to. It came with no instructions, no help, and when I google this problem nothing pops up. Pretty annoyed at this point that i'm going to have to also change my wires now and also annoyed at being so put-out by what (apparently) everyone else knows about. ....so how do I connect to these brass terminals???? Those are for the horseshoe connector that is a part of every DS-II system! Obviously someone has butchered your ignition, but the proper connector pigtail is cheap in the aftermarket. I had to replace mine about a decade ago. ETA link: https://www.amazon.com/Dorman-Help-85848-Ignition-Socket/dp/B000C5G8R2 Link to comment Share on other sites More sharing options...
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