MR2 Turbo Ignition System Maintenance

The MR2 Turbo seems to be very intolerant of poor or worn ignition components. A turbocharged car needs a well-maintained ignition system because the spark has to work harder to jump through the denser fuel/air mixture. If your car has started stumbling or hesitating while under boost, it is likely that one or more of your ignition components is in need of replacement. The most likely candidates for these problems are:

Spark plug wear causing increased gap
Worn distributor cap and/or rotor
Spark plug wire insulation breaking down causing leakage through valve cover

The spark plugs can be changed for very little cost, approximately $10-15 for a set of four. If changing these doesn't help, move on to the distributor cap and rotor, which can be purchased from the parts department of your local Toyota dealer for $30-40. If the problem is still present you might try replacing the plug wires, but since these are a more expensive item it might be better to temporarily swap them with a known-good set from a friend's car before spending the money on new wires.

If the problem is still present after replacing the above components, I suggest asking for advice on the MR2 mailing list or the MR2 message board. There is almost always somebody on the list and/or board that has been there before and is willing to help.

Ignition Timing

Before you start replacing parts to fix your stumble problem, first make sure you check your base ignition timing. Many people (including me) have found that the base timing on their MR2 was set incorrectly, which can cause knock under boost. The computer detects the knock (via the knock sensor) and retards the timing to prevent it. This causes stumbling and hesistant acceleration when transitioning from off-boost to boost.

Try my Ignition Timing page for instructions on how to check and set the base ignition timing on your MR2 Turbo.

Sources and Part Numbers

OEM Spark plugs: 90919-01180 (01/1990 onwards) [-R8 for a pack of 20]. This is the part number for the OEM “Nippon Denso” spark plugs. These are probably platinum plugs and will be horribly expensive. General list wisdom is to replace the stock plugs with copper-electrode NGK plugs.

I use NGK BKR7E plugs, which are one step colder than the stock heat range and so help conduct a little more heat out of the combustion chamber without running so cold that they foul. Note that some suppliers find NGK plugs by their “stock number” instead of the part number. Quite why there are two numbers for the same thing is a mystery to me, but the stock number for the above plug is 6097. I've had good success with these plugs and I recommend them. They can be difficult to obtain though. I get mine from Monarch Products in California (quote: “If NGK makes it, we stock it!”). Telephone (888) 800-9629 or (909) 672-8501 or visit their web site at http://www.thengksource.com/. They also stock NGK plug wires and O2 sensors, which may be useful to some.

OEM distributor cap - part numbers 19101-88363 (01/1990-01/1992) and 19101-88364 (01/1992 onwards).

OEM distributor rotor - part number 19102-74040 (01/1990 onwards).

OEM plug & coil wires - part numbers 90919-21485 (01/1990-01/1992) and 90919-21536 (01/1992 onwards). There are many aftermarket plug wire manufacturers; you might want to obtain advice and opinions from others that have tried them before choosing. I still use the original OEM plug wires without a problem after several years.

OEM distributor housing O-ring - part numbers 90099-14106 (01/1990-03/1991) and 90099-14090 (03/1991 onwards). There is a note in the EPC that the newer part can be substituted for the older part if necessary. I included this part here because people occasionally ask on the MR2 mailing list for this part because they have an oil leak at the distributor after removing and replacing the distributor.

Distributor housing - part numbers 19235-88363 (01/1990-11/1993) and 19235-88040 (11/1993 onwards). This is the part of the distributor that attaches to the end of the valve cover. It does not include the cap and rotor.

Distributor assembly - part numbers 19100-88363 (01/1990-01/1992) and 19100-88364 (01/1992 onwards). This is the entire distributor assembly. It is apparently quite a bit more expensive than purchasing the distributor housing, cap and rotor as separate parts. I have no idea why this might be. Thanks to Jeffrey Ho-See for this information.

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