88 Town Car random misfire

[drhill]

cruise did work last time I tested it, shoot

[DerekTheGreat]

I think I remember kishy discussing this in his thread: kishy's 1991 Grand Marquis - GrandMarq.NET - Panther Headquarters. Something about the length of the sensor's arm and/or the solenoid(?) deals on the passenger wheel well getting sticky.

[kishy]

I think I remember kishy discussing this in his thread: kishy's 1991 Grand Marquis - GrandMarq.NET - Panther Headquarters. Something about the length of the sensor's arm and/or the solenoid(?) deals on the passenger wheel well getting sticky.

I did touch on some operating theory but nothing that really seems to deal with this problem. Gadget did talk about the VSS thing on one of my threads as well, but not in any more detail than he did here.
I seem to recall that there is an allowable/designed amount of vacuum to pass through the EVR, but I don't remember why I think that. When I was substantially more not good at troubleshooting things 10 years ago, I did try to figure out suspected EGR problems on my 91 (which functions the same as 88), but I never got into it this far really.

With my 85 more recently (which does not really work the exact same way - same theory but different parts) I did a deeper dive on it, but that also doesn't really help here.

Basically, if an EGR code is present, my understanding is that the system cancels EGR usage and it won't bother you.
If the EVR is allowing the EGR valve to open at incorrect times, that is undesired behaviour and will cause a miss.
Best thought at the moment is that the new EVR is either defective or designed wrong (e.g. for a different vehicle with a valve that has some varying specification that makes this not work here)

drhill out of curiosity, what new EVR did you purchase (brand and part number)? And is the plastic cap on top gray or black? I have no insight as to why I'm asking this at the moment, just data collection in my brain.

[drhill]

it was a standard motor products VS77, grey cap. My OEM one is black cap....

For now I'm just leaving the EGR vacuum hose off the EGR and capped. I'll figure out smog but since it runs fine I can live with it like that unless I'm giving up a lot of MPG etc?

[sly]

If the battery was not disconnected, that may be required for proper operation as learned data may need to be relearned with the new part. Not sure if the EVR is included in that learned stuff though.

[gadget73]

Can stick a vacuum gauge on the green line to confirm what its doing. Probably have to tee it in with the EGR valve since the system does indeed stop trying to do stuff if it doesn't see the position sensor respond. if its behaving itself it should gradually increase vacuum, if its being dumb it will just switch full open.

At idle it shouldn't be getting any vacuum. if it is, maybe unplug the electrical connector and see if the valve is being commanded open for some reason, or if its got a problem that is passing vacuum when it should not.

as for the VSS thing I really have no further detail. My car had VSS codes because I have a later mass air ECM in there, and in 1986 there was no VSS signal to the ECM. I just ignored it since I really didn't think it mattered. At some point I decided to hook up the VSS wires just to make the code go away. It also changed the behavior of the off-idle hesitation that I had been ignoring for a long while. Further poking using a vac gauge and a simple "what happens with it plugged in vs what happens with it not plugged in" indicated that the EGR vacuum signal was different with and without the VSS. Why? Not a clue. That also ultimately led to finding out the EVR not acting as a regulator but as a switch, and cleaning it made the problem go away completely.

[kishy]

RE Grey vs black - I don't know if it matters or not, but I've seen both parts offered and both parts on varying vehicles.
My 91 has a black top part which I installed 10 years ago, it was BWD which I'm pretty sure is one of Standard's sub-brands, I think.
When I recently bought a new one, I was suspicious that it has a grey top, but haven't figured out the relevance yet as I didn't need to use the part to solve my problem.

Are the vacuum lines the original setup with the molded plug for the connection to the valve? If they are replacement lines, maybe they are reversed? I think they must be connected a specific way or the EVR flows vacuum wrongly, but I'm not 100% sure about this.

[gadget73]

yeah they do have to be connected the right way. I don't remember what happens if they are backwards but it definitely doesn't work correctly.


not sure the cap has much to do with anything. I think the one on my car now is a grey top aftermarket, original was black. That cap holds a foam filter to keep dirt out of the EVR. The foam is prone to breaking down and turning to dust after a while on originals.

[drhill]

I will hook up a vacuum gauge and do some testing. preliminary results found that I do have some vacuum at idle at the EGR with EVR plugged or unplugged. I'll get better and more detailed info shortly

[drhill]

I'm back at this mainly because the car pings like crazy with load on the highway. I can make it go away with higher octane gas but that's not really a long term solution. SO, it appears I have to tee in my vacuum gauge and monitor it at various throttle positions while driving and make sure it's steadily increasing with more throttle? Also, I can test it with postion sensor unplugged as well I guess? I can also remove the EGR and double check it's not plugged up? But that's unlikely since it no longer misfires if I unplug and cap the green hose.

[gadget73]

if the ECM sees the EGR valve open, it will lean out the fuel mix and advance the timing with the assumption that an open valve means there is exhaust flow. If its clogged but open, it still advances the timing and leans it out, but without the exhaust gas its probably too lean and too advanced. If the valve doesn't open, it doesn't change the timing or fuel so that would make sense that it doesn't ping with the green line off.


Don't need to remove the valve, just pull vacuum on it and see if it runs horrible at idle. If it runs bad or stalls the passages are fine. if no change or barely any change, there isn't any exhaust getting through. At that point you'd have to decide if you want to pull the intake and try to un clog all of that, or just plug the EGR line and leave it be.

[drhill]

if the ECM sees the EGR valve open, it will lean out the fuel mix and advance the timing with the assumption that an open valve means there is exhaust flow. If its clogged but open, it still advances the timing and leans it out, but without the exhaust gas its probably too lean and too advanced. If the valve doesn't open, it doesn't change the timing or fuel so that would make sense that it doesn't ping with the green line off.


Don't need to remove the valve, just pull vacuum on it and see if it runs horrible at idle. If it runs bad or stalls the passages are fine. if no change or barely any change, there isn't any exhaust getting through. At that point you'd have to decide if you want to pull the intake and try to un clog all of that, or just plug the EGR line and leave it be.

Thanks for the insight. It does ping on the highway with the green vacuum line capped. That is my concern, especially understanding how the system works as you laid it out...

[drhill]

I may try to pull codes again...I keep thinking if any of the sensors have gone bad (Air temp, coolant temp) it would pop a code but I had just the "11" all good code

[gadget73]

Is the base timing where it belongs? Some of these things are super bitchy about that and absolutely do not want more than 10 degrees. I know some people have run 14 degrees or more with no issue but none of mine want any advance. Also not impossible you have funky injectors that aren't really doing a good job, and/or carbon buildup thats causing problems.

[drhill]

I pulled vacuum on the actual EGR unit and it did stumble and want to die. So that is working well. I will get another timing light and check base timing, I haven't used one in many years since I've been in the LS world. I will also use some seafoam to clear the valves and chambers of any carbon. I did clean out the injectors actually, pulled filter baskets and did a ghetto cleaning with a tire valve stem, a can of carb cleaner and a buddy pulsing them with the battery. worked well and one or two were not great but cleaned up nicely.