SOLVED: OBD1 Coolant Temp Sensor Code, S52 No Hot Start

[Nick's e30]

Hey all.

I just put wraps to an OBDI converted S52 swap. I'm having random no start problems.

Once the car is running, it's fine. No hiccups, no hesitation, nothing. Runs great and pulls great.


The best way to describe the no start is by the audible difference in startup noises. When the car is going to start, it cranks much slower and then fires up!
However, when the car is going to fail to start, the cranking is at least twice as fast, and obviously the car doesn't fire.

Additional information:

I performed a second compression test and leakdown test. Compression was in the low-mid 180s on my brand new tester within 2psi on each cylinder, leakdown was less than 12% in each cylinder. From what I can tell the motor is healthy, so I'm ruling that out.


I'm starting to get deeper into suspecting some electrical issue. After finally connecting the issue to the fact that the car only has this issue starting again when it's fully warmed up, I got a hold of a Peake Diag tool, which gave me code 29 for my coolant temp sensor, along with code 4E for my evap (which is unhooked at the moment, I thought I lost or sold the evap sensor with my m20 and found it this weekend.

Any insight to this?

This seems to be...SOLVED: Coolant sender and sensor wires were reversed. Both senders were the same color. Oh well.

[BlackSpeed66]

I would check your grounds if you haven't already. I was having some goofy issues on my swap - intermittent gauges, no-start, charging - and it was the damn ground cable on the side of the block. The bolt on it was like 2 turns loose, likely due to operator error. No issues since.

Now if I could just figure out why it's running so damn rich...

[Nick's e30]

I would check your grounds if you haven't already. I was having some goofy issues on my swap - intermittent gauges, no-start, charging - and it was the damn ground cable on the side of the block. The bolt on it was like 2 turns loose, likely due to operator error. No issues since.

Now if I could just figure out why it's running so damn rich...

The shop that built my exhaust told me my ground wasn't enough (it's a braided ground like I see a lot of folks use but it's not shielded) so I went ahead and ordered the e36 OEM one. I'm going to put that on when it gets here.

With your no start, would the starter turn over but the car not fire up? That's what I'm dealing with, but once it's running and decides to fire up, it's fine.

I was also recommended to perform a leakdown test, the lack of fire-up and faster start may point to lack of compression? Or just higher electrical load available to the starter when the injectors/spark plugs aren't firing at full strength? I just have trouble putting any belief behind bad compression because the car runs so well and smooth when it is running.


As an aside to the richness, I'm running a TRM chip and the car runs pretty rich. Which chip are you using (or is it stock?)

[BlackSpeed66]

The issue mine was having is that I'd go to start it - everything would light up on the dash as normal, I'd turn the key - and then nothing. Like it was mimicking a dead battery, but wasn't actually dead (which all makes sense now after figuring out the issue). But grounds do weird things. When the car would actually start, the charging wasn't right (voltmeter was wacky), temp gauge and my VDO oil temp/pressure gauges were all wacky. All of that stuff grounds straight through the block


I'm running OBDII with one of Dave's tunes on an otherwise stock ECU/engine. I'm not sure if a lot of these tunes run rich by default or what... Gonna smoke test the car again here shortly to rule out any vacuum leaks.