Crank no start. No lights on dash

[craigsmith86]

Afternoon all,

I'm several months into an engine rebuild and refresh on my '86 Mk1a. Engine is sorted, installed and ready to go but I've run into an electrical issue that's left me puzzled.

Here's some background:

After refitting the engine loom I had heat and smoke coming from the ground strap on the head (fitted on the engine hanger near the timing cover).

I immediately disconnected the battery and replaced the earth. Investigated the earth issue and stupidly realised I'd painted the transmission and starter motor earths points without cleaning them off. Cleaned all reattached the earths.

Car now cranks strongly and has fuel pressure at the rail but has no spark whatsoever. When the ignition is 'on' there are no dash warning lights (besides handbrake) but all other interior electrics are working fine. The coil pack and the igniter pass the inspection steps in the BGB.

Assuming I had burnt something in the loom(s) I removed both the engine loom and the loom that runs from the boot, to the fuse box that terminates in the passenger kick panel. Both looms has signs of wires being hot (which may not have been related to my issue) so I replaced both looms with second hand ones from a working car.

Same issue. Crank. Not spark. No warning lights.

Next thought was a fried ECU so today I've replaced the ecu like for like. Same story.

I'm now at a total loss. Everything I expect to be working is working except the dash lights and spark.

I would like to go through the loom wire by wire from the ECU but I only have access to an 88 BGB which has different pinouts on the ECU so diagnostics is pure guesswork. Any advice would be much appreciated. I really want this car back!!

[jimi]

Sounds like a fuse or bad wiring. Have you checked all the relevant fuses in the engine bay, drivers footwell and front boot fusebox's ?
A PDF copy of the Toyota Electrical Wiring diagrams is available in the Downloads section https://mr2oc.co.uk/downloads/technical-stuff/mk1.html which will be accurate for your car (it 's the best electrical manual I've found for UK/EU MK1's)

There's a junction box hidden in the driver's footwell up behind the dash (it's shown in the above manual as JB3) it's been known to suffer from heat damage caused by overloads, bad/slack connections or even an incorrectly connected battery.

[craigsmith86]

Thanks for the suggestion,

I checked the fuse box from the diagrams and all the connections were fine and I don't see any sign of heat soak in the wires so I'm not convinced there is an issue with the wiring at the front of the car.

I'm not beginning to think that the old alarm system (which I have no knowledge of) might have been partly wired into the loom before I removed the engine and unplugged everthing. There were aftermarket wires running in the engine bay which I suspected were for long removed latch sensors and an old siren that was still mounted so I removed those during the rebuild.

Perhaps an old alarm circuit was bodged to keep the car running when the alarm was removed? Does anyone know which circuits were commonly tapped into for alarm installs?

It's driving me mad!

[jimi]

Guessing will not work, have you checked for error codes ? does the check engine light come on at all while checking for codes ?
If not your only real option is to use a multimeter and the electrical diagrams to trace each circuit out and confirm you are getting voltage at all the places necessary for the engine to start.
I'd start with the obvious, find out why there are no dash warning lights with the ignition on. Start by checking your are getting power either side of the 7.5A Gauge fuse, if no volts both sides use the diagrams to find out where that fuse is supplied from i.e work back to the battery checking for voltage. If there is voltage on one side and not the other then the fuse or holder is faulty, if both sides then work forward from the fuse checking for voltage at each connection point shown on the diagram.
If your not confident in using and understanding the diagrams and the meter readings then get help from someone who is or get an auto electrician on the job.

[craigsmith86]

It's been a while and I haven't looked at the car much the last few months. I spent the day on it today and think I've found a few suspect issues.

I'm pretty confident with a meter and have checked all the grounds today carefully to make sure they're all solid and clean. The ECU is getting power from the battery and the grounds under the fuel rail are reading fine. Fusible link is good. I've been through both engine looms I have to hand with a multimeter while they're out of the car and can't find anything different between the them so I don't suspect an issue with the engine loom.

I've just dug out an '86 wiring schematic which will help me confirm I'm checking the right coloured wires out of the ECU but so far I've found that B+ and B- aren't receiving power from the ignition switch. I'll need to confirm that using the schematic.

Earlier today I wondered whether the bulbs in the cluster were just fried. Having removed the instrument cluster all of the bulbs are fine.

Now I'm thinking that the ignition coil could be iffy, it passes the beach test from the bgb but I know they can still be bad even when they're within tolerance.

I will definitely pick my way through the fuse box checking for 12v at each end of the fuse holders just in case there's a loose wire, but I've had two different passenger side looms fitted and both have produced the same issues.

Thanks for your help.

[jimi]

Be quick it won't be there long
LINKY

[craigsmith86]

Thanks, that's really helpful!