GM/AC Delco D585 "LQ9" Coil Issues, Fixes, and Warranties

There have been several issues with the use of the ACDelco D585 "LQ9" Coils for high performance work. With upwards of 500 kits sold world wide, We have monitored problems arising and have developed the following fixes.

1.Early in the use of these coils Many of the ECU manufacturers were recommending dwell times of 5-6 MS. This seemed to work well but soon reports of blown engines began to appear, apparently with the LQ9 coils as the cause. It was found that when excessive dwell is used, the coils will sense a charge overcurrent and self discharge in advance of the ignition pulses's falling edge, effectively advancing the the spark to a dangerous and sometimes destructive degree. The fix for this is to limit dwell to 3.4 MS or less. This dwell value with the GM coils has supported boost numbers in the 30-40 range and whps in four figures.
2. The AC Delco D585 "truck" coils were designed to work with resistive plug wires and require some resistance to avoid excessive output current, and resulting coil failure. For this reason, when using the coils on-plug, It is mandatory that resistor-type plugs are used. The NGK "BKR" series spark plugs have been used with good success on both 2J and RB applications with the Mojo kits.
3.There have been instances of the GM coils causing RF interference that injects noise on the JZ engines' cam sensor. The JZ kits' coils now are shipped with shielding that has eliminated all RF problems. The RBs use optical cam and crank sensors that are immune to the small amount of RF interference caused by these coils. Converting the JZ's Cam and Crank sensors to Hall effect units also provides resistance to RF interference.
4.In the last several years there has been a flood of cheap knockoffs of the D585 coils, with most being grossly deficient to the OEM parts in terms of performance and reliability. In fact, the newer series Genuine AC Delco coils have been being returned with complaints of failures and poor performance. This has been verified with Mojo's bench testing. As a result, we have stopped selling new coils, only used/cleaned/tested OEMs. These coils carry a 90-day warranty and we have been known to replace coils slightly older than that.
5. There was a period about a year ago that Mojo provided harnesses that had weak crimps in both the coil connectors and the multipin Deusch connectors. These have been repaired/replaced under warranty. All the Mojo - produced pieces for GM coil conversions carry a lifetime warranty against defects. To get warranty service the parts must be returned unmodified, and shipping will be reimbursed.
6.It has been the opinion of some users that the GM coils do not like the heat encountered in the plug valley of the JZ engines. We have yet to quantify heat problems (Rick has been running the truck coils for 5 years in Florida heat with no problems) but will continue to monitor this. The copper shielding on the newer used coils provides some measure of heat reflectivity that will lower heat absorption via radiated heat, and the Mojo bracket system is designed to minimize conductive heat transfer. See 7.) below. The problem described there could be mistaken for deterioration due to heat.
7.In troubleshooting instances of the coil performance deteriorating after a period of no problems we have found that sometimes the old stock power wiring and fuel injection relay is not supporting the increased current draw of the GM coils. In several such instances recently, an increasingly worsening low rpm breakup was fixed by using a relay to switch battery power to the coil harness's power leads, with the stock 12 volt power wire used for relay coil trigger. We can provide custom harnesses that provide this upgraded circuit.

While is is felt that all the concerns for using the LQ9 coils have been addressed, Mojo Performance will continue to monitor customer responses for actionable problems.