So I did a complete tune-up on my 1989 C4 auto, completely stock. I did rebuilt Bosch injectors, new DUI coil/cap/rotor, matching Performance LiveWire wires and new denso platinum TT plugs gapped at 0.055 per the instructions from DUI. All was GREAT after doing the install...took me about 6-8 weeks to get everything done. Today I get the plugs installed and decide to drive the car to soccer practice, about 30 mins away. Everything went fine over to practice. Car was running like a dream. After practice, I am coming home and notice my Service Engine Soon light flick on and off instantly with just the slighest blip with the engine. This happens a couple times on the way home. I get home and need to immediately run my mom to drop her C5 at the shop but I have the hood open checking everything and the car nearly stalls out. Purrs like a kitten and then WHAM...nearly stalls. Heading over to her shop (again 30 mins away) the same thing happens a few times...lose power for half a second and the light flickers then back to running like a champ....I actually thought it was an issue with the over-drive at first but I soon find out that is not the case. Waiting for my mom to drop her car I am parked and it happens again, just sitting there...we pull away and I am sitting at the stop sign and the car dies. Try to start it...engine cranks but nothing...crank again...nothing. Pop the hood and knock on the top of the distributor...magic...car fires right up. On the way home...I get the flicker a couple times but I make it home.

Question to the masses...I see that several people online have had issues with the DUI being DOA or soon after. Am I crazy...is it really the brand new coil and cap? I am thinking about running locally and spending the $$ to get a cap and rotor and throwing the old coil in that to make sure its the cap...my biggest issues is, I opened up the gap on the plugs. Will this have that much of an impact on testing? Did I open the plugs up too far? They are between .052-.055 max. I actually kept them a bit under the .055 because I thought that was a bit excessive but its what they recommended. I was really looking forward to enjoying the car this fall. I spent the last couple months getting it ready. Really need some help, any suggestions or insight is more than welcome. I have already reached out to the distributor about a replacement for the cap. No idea how long that will take etc...

 

You said you tapped on distributor and it started. Id look at the wireing connectors that plug into the hei. Pull them off make sure they are tight and clean and snap them back in. While car is running wiggle the connector and see if she acts up. Those connectors get loose over time.

 

Thanks @FostersPerformance but nope. I wiggled all the connections to the cap and not even a little blip. Also wiggled all the plug wires too...but again nothing. It started right up this am...no problems. Thinking maybe me tapping the top of the cap was just a coincidence that it started afterwards...not sure. When I have some time, I will pull the connections again and clean them. Should I use some di-electric grease on them?

 

I always use dielectric on most connections but im also a Marine tech so its common practice to do so.

 

You said the SES light came on at one point. Did you check to see if there were any stored trouble codes?

 

Thanks @TA . The SES light isn't staying on so I assumed it was not storing a code. It literally blinks...honestly I couldnt even tell which light was blinking...just had to remember where it was on the panel then see when I turned the key to ACC.

 

So, in speaking with someone, they indicated it could be the distributor pickup...? So I am going to put a new pickup in. Should be here next weds. Also, I thought about the ignition control module. I did not replace that however could that be an issue? I haven't ordered one because I wasn't sure if I should upgrade to something like the Dyna-mod. Whats weird is that I did not have any of this issue prior to replacing the cap and coil. The car was running rough but that was due to 3 bad injectors. I could drive it around and the performance was just terrible but nothing like this happened. Any suggestions/input on the direction?

 

I have one of these on my boat motor. I suspect that the DUI coil is too much for the stock ignition module. Call DUI for an ignition module recommendation. They are very helpful.

 

@Siveck Thanks so much...will do.

 

Holy smokes...just called Davis. They could not have been nicer. He thinks it the coil. He is shipping me a new one to verify. 5 stars for their customer service....gosh I love calling and talking to someone in country.

 

Yes, they have excellent customer service.

 

That is great that Davis Unified Ignition responded and helped you! That is good to know as I have some of their parts on my L98 ignition! The parts I have on my L98 are eight to ten years old and are working just fine.

I have a nasty 12.25-1 Compression ratio 427 in my 1968 C3 and MSD suggested that I open the spark plugs up to a big gap like you were discussing earlier. I started to go through coils every few years and finally found out that the big gap was harder on the regular coils. MSD told me to use a higher grade of ignition coil as that would solve my problems. The coil they suggested was over $200 so I put that thought on hold. My MSD ignition consists of a MSD Billet Distributor and Coil connected to a MSD 6AL and a digital retard box. The sparks with a .055 gap would still get their electrodes burned away in a few months. I tried using a set of Iridium spark plugs and that was a disaster. Now I am back to the AC Delco rapid fire spark plugs that work fine and are cheap.

My new to my C3 EFI system from Holley will be taking control of my ignition system. I am using the MSD distributor with the Sniper EFI so I can keep my mechanical Tach drive. Holley wants to use one of their own distributors but the MSD will work. Getting the ignition control done by the same box that is doing the Fuel injection will give the system better control of the entire engine.

Thanks for the update on the folks at Davis! They seem to be here for the long haul and make some great products.

 

My DUI was supplied with the wrong reluctor so the timing was way out. I rang Davis and they sent a new correct one which solved the problem. Whilst investigating the issue I also noticed that there was paint under the coil ground connection Which I removed.

 

@ctmccloskey good info! Thanks so much. I was very concerned about opening up the gap but did it anyway. Doing the plugs is not much fun but with patience and practice, its not the worst. I think I will be switching back to the delco plugs and keeping the gap closer to the .035-.040 as has been discussed in other threads.

BTW...swapped my old cap and stock coil back in yesterday...no issue. So its got to be the coil as Davis thought. Should have the new one Weds. I wanted to replace the old coil because its the original, otherwise I would have just got a new cap and rotor, and used the old coil. Wasn't really looking to go crazy as most of the feedback is the high output coils are kind of a marketing ploy...not really giving you the performance claimed.

 

I think that is true. I've never seen dyno shoot-outs of ignitions system upgrades, like you see with cams, heads, intakes, headers etc....that have shown any meaningful gains. In fact, you almost never see ignition upgrade dyno shoot out at all! Why? Likely b/c it will show what the ignition mfg's don't want you to see; little to no gain. Engine Masters just did a test of ignition -and they didn't want to do it; they did it to their chagrin, due to the volume of viewer's comments/demands for that test. On a ~630 hp engine, they went from standard electronic ignition to a MSD high output coil, MSD "multi strike" box (6AL2). They picked up 2 hp (631 up to 633) and lost 4 lb ft at peaks.....basically a wash.

Their take away was that you buy this high end ignition stuff for reliability. I agree and "get it"...unfortunately, I see way too many posts on forums about "high end" aftermarket ignition parts that fail. I don't think that they're as reliable as OEM parts. I've even had a Jacobs ignition coil fail on me once, so went back to a stock coil, which worked great. I've never had an OEM coil fail. My take-away is that if you're not running boost and super high cylinder pressures, it's hard to beat a stock "HEI" or modern electronic ignition system.

 

Thanks @Tom400CFI ...I think a lot of these marketing gimmicks get newer guys like me. I've read a bunch of articles that basically re-iterate what you are saying. My mistake was thinking the reliability would be the same or better than the OEM part. I hope its just a bad part and the new coil will not fail the first day of install. I have no faith that corvette mods would honor anything. They haven't even responded to my initial out reach with issues. Luckily Davis is a standup company and they are taking care of me.

 

Aftermarket companies don't have the resources (money or equipment) to develop and test parts like the OEM guys. It's damn rare for aftermarket companies to be able to offer parts that are more reliable or robust than OEM parts.

 

What I think is interesting is that after market ignition manufacturers often recommend widening the spark plug gap but in n many cases that’s the opposite of what you should do. For a stock engine the engine manufacturers recommendations are probably best.
Modified engines with higher compression or forced induction will typically require smaller electrode gap settings (to ensure ignitability in these denser air/fuel mixtures) as the voltage requirement at the electrode gap is increased due to higher combustion pressures. My 11.5:1 compression racing 84 runs 30 thou spark plug gap.

 

So over the weekend, I put back in the stock cap/coil and ran it all week, zero issues. My new cap and coil came last night from DUI so we will see if the new one does not cause the issues again. Should have some time today or tomorrow to put it in. Anxious to see if the issue re-occurs.