Rough Running - Ignition Coil out?

[KPW]

Out driving this morning and all of a sudden the car (1991) changed character pretty severely under load. Sounded much more boomy (low frequency) and felt like it was missing. Got home and idle was shaking the whole car.


Paged through some of the forum here to get some ideas. Main suspects likely ignition or fuel.



Fuel: Used Marc Haibeck's injector ohm process while still hot - nothing shorted in the primaries (a bit higher than expected, but my injectors are the yellow Bosch?). Did not check secondaries - in any case they're not active at idle.


Ignition: Checked ohms across the coil pairs (plenum still on, just through the plug wire ends). 1/6, 2/3, 4/7, 5/8. All gave me 20k + ohms, except 1/6 which showed open circuit (infinity) between them. Figure we're probably going under the plenum, so off it comes (first time, not too bad!). Pulled the wires off and checked again, still open across 1/6 at the coil. Others come in at around 6k ohm. My guess is a bad 1/6 coil. Sound reasonable?


Now that the plenum is off and I'm shopping at jerrysgaskets, anything else I should go ahead on while I'm here? I'm planning to do all the coils and wires at least. Might go dig for the starter solenoid contacts too...

[Young1]

Replace Vacuum solenoid for secondary acuators. Standard part number VS124. Do a search plenty of info and what to do under plenum. Yes shine up the copper contacts of the starter solenoid. I use a die grinder stone in a battery drill.

[KPW]

Thanks for the tips, Young1.



To wrap things up here, the car is back together and running smooth once again. Some things I noticed during this process:

• Next time I'll make sure I drain more coolant than I think I need to. I followed a nice write-up that suggested draining the coolant using the hoses that connect to the plenum/throttle body. I still needed to pull some more to get down below the injector housing level - found out the hard way and spent a bunch of extra time cleaning up coolant. Definitely worth a little more effort at the beginning to avoid cleanup later.
• Old plenum gaskets completely fell apart on the way out. Possible that the last person to be in here added some adhesive...lots of cautious time spent cleaning off the surfaces with a scraper. I applied some silicone spray to the top surface of the new gaskets prior to installation - hoping next time I'm in here it will at least be easier to remove the gaskets, if not enable re-use.
• The valley was gross! Clearing out the drain was much overdue. I did find a plenum screw I had dropped (and a MAP sensor bracket screw someone before me had dropped).
• Solenoid contacts shined up nice with the die grinder stone, and were needed (I'm at 40k miles or so). I have to imagine the starter sitting in a little bit of the valley "soup" wasn't helping either. Feeling more confident in avoiding "no starts" moving forward.
• While the service manual is handy - this forum is just as useful. We're lucky to have access to such a community.

I will say it's nice to have a successful plenum pull under my belt. Nice boost of confidence to understand the effort required, so that the next time it doesn't seem so daunting.

[A26B]

Thanks for your "follow-up" post. Always useful to others to know how a problem was solved and courteous to those who offered suggestions..

[Paul Workman]

Originally Posted by KPW

Thanks for the tips, Young1.



To wrap things up here, the car is back together and running smooth once again. Some things I noticed during this process:

• Next time I'll make sure I drain more coolant than I think I need to. I followed a nice write-up that suggested draining the coolant using the hoses that connect to the plenum/throttle body. I still needed to pull some more to get down below the injector housing level - found out the hard way and spent a bunch of extra time cleaning up coolant. Definitely worth a little more effort at the beginning to avoid cleanup later.
• Old plenum gaskets completely fell apart on the way out. Possible that the last person to be in here added some adhesive...lots of cautious time spent cleaning off the surfaces with a scraper. I applied some silicone spray to the top surface of the new gaskets prior to installation - hoping next time I'm in here it will at least be easier to remove the gaskets, if not enable re-use.
• The valley was gross! Clearing out the drain was much overdue. I did find a plenum screw I had dropped (and a MAP sensor bracket screw someone before me had dropped).
• Solenoid contacts shined up nice with the die grinder stone, and were needed (I'm at 40k miles or so). I have to imagine the starter sitting in a little bit of the valley "soup" wasn't helping either. Feeling more confident in avoiding "no starts" moving forward.
• While the service manual is handy - this forum is just as useful. We're lucky to have access to such a community.

I will say it's nice to have a successful plenum pull under my belt. Nice boost of confidence to understand the effort required, so that the next time it doesn't seem so daunting.

As Jerry said: Thanks 4 the follow up! And, I too recommend spraying one side of the plenum gasket w/ silicone spray. The plenum side is clean except for the area circling the coolant port - the plenum side and gasket get some 3M gasket adhesive to keep the gasket stable around the coolant port (past experience with leaking there fixed w/ the 3M adhesive, I found).

And, FYI, installing the gasket as you did (w/ the silicone on ONE side), I have been able to removed the plenum one or two more times w/o having to replace the gasket(s). (But, I keep some of Jerry's gaskets on hand, "just in case"!)

And, kudos on the info on the condition of the stater solenoid contacts and mileage! Your experience falls right in line with a few others I have noted in my maintenance log - that is servicing likely required every 40k miles (give or take). I experienced a intermittent NO START as result of those contacts (and the bridge ring connecting the contacts) at just over 40k miles, and now (counting you) reports from 4 others experiencing either some sort of NO START or intermittent starting issues @ ~ 40k miles.

NOTE: I opted to remove my Secondary Port Throttles (SPTs) and plugged the coolant passage leading to the throttle body. As result, there is no need to drain coolant to pull the plenum - just another nice perk resulting from either plugging, or as Marc Haibeck recommends, bypassing the coolant thru the throttle body via a tube running under the plenum. (Marc's method better facilitates removal of air from the system when also jacking the passenger side up to bring the air bubbles to the reservoir tank.)

A plenum pull is "A RITE OF PASSAGE"! Welcome to the BROTHERHOOD OF THE BEAST!!

[XfireZ51]

Side Question. U say u are using yellow top BOSCH injectors on a 91 IH? Are these Bosch III injectors?

[KPW]

Fair question. I?ll admit the injectors were installed prior to me owning the car, so I?m running a bit on hearsay when I say they are Bosch, also I?m not sure of what was involved in the installation.

Here?s a photo I took while the plenum was off - maybe a learning opportunity for me?


Sent from my iPhone using ZR-1 Net Registry

[XfireZ51]

Its doubtful they are Bosch IIIs. They unfortunately aren?t compatible w the 90-92 IH.

[dredgeguy]

Perhaps Chevy?
https://www.southbayfuelinjectors.co...fuel-injectors

[XfireZ51]

Originally Posted by dredgeguy

Perhaps Chevy?
https://www.southbayfuelinjectors.co...fuel-injectors

I?d be asking if they are reman! I also don?t buy the 1% flow matched. If I am replacing injectors, I?m getting them flow tested myself before installing.