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. :cheers:



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]

Thanks for the tips, Young1. :cheers:



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 (http://r.tapatalk.com/byo?rid=90383)

[XfireZ51]

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

[dredgeguy]

Perhaps Chevy?
https://www.southbayfuelinjectors.com/zr1-chevy-corvette-1990-1992-zr1-fuel-injectors

[XfireZ51]

Perhaps Chevy?
https://www.southbayfuelinjectors.com/zr1-chevy-corvette-1990-1992-zr1-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.

[ZR1CK]

I have a '91 with just under 27k miles and am on my 3rd set of ignition coils. Bought the car in '01 with 10k miles. Replaced the Delco's because one was miss firing at around 18k miles with Accel. Had same problem with them at just over 1k miles. Found out that the are no longer made in USA. Third set is BWD, made in USA, and just recently had one of those fail. Don't know what the problem is, maybe they can't handle the heat. Any thoughts?
Rick J

[A26B]

Did the bad coil actually test bad once it was removed from the coil pak base? With the failures you describe, I would be checking the harness connectors to the base and possibly even the base. Do you recall which coil failed for each of the 3 different events?

Your problem is certainly not the norm.

[ZR1CK]

Hey Jerry, good to hear from you, thanks for responding. It all started one day when the motor seemed to be skipping. After eliminating that it was the plugs, I turned to the plug wires and ignition coils. The way I checked them is by using my timing light to see if the plug wires were carrying any signals. Six of 'em were signaling fine while two were intermittent, and those two were tied to the same coil. I then popped off the plenum, checked all the plug wire connections at the coils, checked all other wiring connections that I could get at for snugness and then swapped two of the coil positions. Put it all back together and ran it, this time two different plug wires were intermittent and tied to the same coil, the same one that was missing prior to the swap. To do another check, I disassembled everything again, removed all 4 coils and took them home (I rent a garage away from home) and installed them one at a time in my '99 Buick which used the same coil application. 3 worked normal and the one that was missing on the "Z" was also missing on the Buick. I decided to replace them with Accel coils because of their reputation over the years. But, at around 1500 miles that same problem occurred. So much for reputation. This time when I took it apart I did check the base plate for continuity and it checked out good. I then decided to check the primaries and secondaries of both the Accel's and the previous Delco's (yeah, I saved 'em). They all read within specs with my ohm meters, both of them, I have 2. The only thing I can figure is that the insulation on the windings is breaking down to a point were they can be read good with the ohm meter but when a high voltage is applied they fail. I figure it's because of the heat on top of the engine. So, this time I decided to replace them with BWD coils as they were made in the USA. :fahne: I have a "thing" about that. I found that the Accel's are made in either Taiwan or Mexico, can't remember which. Anyway, the BWD's were working great for about 8k miles. Same thing, one coil failing. Coils shouldn't breakdown that soon. My '92 Blazer has over 200k miles with the original coil and it works 4X more than the "Z" coils. I'm gonna need to make some kind of a change. I'll let you know.
Be "Zeeinya"

[Paul Workman]

I've nothing to add to your conclusions or decisions: I'd be doing something similar.

However!! (and you did touch on this too), HIGH VOLTAGE devices can frustrate attempts to "OHM" them out using the standard DVOM/VOM. And, the reason (in case some are wondering) is high voltage can punch through (arc!) insulation that has cracked or deteriorated/weathered), or current pushed by high voltage can take a surface route to ground, especially if the surface is covered with moisture or salt or rust...any number of impromptu conductors. And, frankly the standard VOM is powered with (at most cases) 1.5 or 9 volt battery(s - neither being high enough to cause arching/shorting and thus being detected by the VOM.

To directly test/measure stuff like wire insulation or continuity requires a tester such as a MEGGER (a high voltage "VOM" used for measuring the resistance of insulation or spark gaps).

However, I doubt you'll ever see a MEGGER at your local auto parts store: would be unusual if you did! So, much as I HATE indirect testing, substitution with a known "good" device may be the next best alternative. But, here's the rub: How do we know the replacement is any good? And, HERE is the place where so many times ppl get in trouble: they ASSUME the 'new' device is good, and therefore if the problem persists or returns shortly thereafter, they don't verify the issue is not withe the new part. (See how often in threads like this where someone says: "It can't be (this or that) because it was just changed a short time ago!" The most failure prone time for a new device is immediately (or soon thereafter) it is first put in service!! Never assume a new part is not bad based on time in service...NEVER! Verify operation.

NOTE: And, since so many parts come from over seas, the trend is a lot of (electrical especially) parts just don't last like the OEM parts if they work at all! Just sayin.

[ZR1CK]

Hey Paul, thanks for your response and additional info and explanations for others out there. I am familiar with a megger as I was an industrial electrician. Being that I am retired now I don't have access to one. And one thing I did do when I was working is to check the operations or work-ability of items, new or refurbed, before installing them, even though my colleagues mocked me, to verify they were good to go. One of the things that greatly frustrated me was to install an inoperable "new" or "refurbed" item. Anyway, I did replace the latest "bad" coil with a same BWD coil. Car runs like it's supposed to now. I also relocated the coil pack from the top of the motor to get it away from the heat. I suspect that that's what was causing the problem. So far the car is running very well. If you are going to Carlisle I can show you what I've done.
Zee ya :cheers:

[XfireZ51]

If you haven?t done it, do the coolant bypass on the TB. Makes a plenum pull soooo much easier and quicker.

[A26B]

Rick,
You have been a thorough as can be, spent a lot of time, but you have confirmed bad coil(s). The fact that it did occur is very unusual. I have a question remaining.... Did the initial coil failures by some coincidence, all occur at the same coil position, i.e. 8/5 location, or 4/7, etc., on the coil base?

[KPW]

If you haven?t done it, do the coolant bypass on the TB. Makes a plenum pull soooo much easier and quicker.


Like the bypass line Marc Haibeck sells? Wouldn't I also need to block at the injector housings to get the full "easier and quicker"?

[Paul Workman]

Like the bypass line Marc Haibeck sells? Wouldn't I also need to block at the injector housings to get the full "easier and quicker"?

Not meaning to get off topic, and certainly not arguing w/ Marc Haibeck, but I drilled and tapped and plugged the TB coolant ports at the IH. To avoid any air bubbles, I remove the cap from the side of the coolant pipe (drivers side) and fill the system there. I've done this a few times now, and haven't had any issues with air bubbles.

That said, Marc's method came to light AFTER I had done the plugging method. And, to do it over again, I would likely go that route instead of plugging the IH. But, either way REALLY makes pulling the plenum a SNAP!.