Mechanic did a gas motor swap on 2003 Prius...shutting down after it starts...

I think the first thing to establish is if the engine is running or is it just being spun by MG1. Are there any fault codes and if so what are they?

John (Britprius)

 

Where are you located?

There may be independent Prius shops around that might 'lend a hand.'

Bob Wilson

 

One of the posters replied to a similar situation for me and this is exactly what the mechanic needed to know to get it running. Thanks again to Chapman! Might help your situation...

Technical question -- Engine Swap | PriusChat

 

The engine is not shutting down, as BritPrius said, it is spinning but never starting. The way the Prius ICE starts is the MG spins it up to 1000 rpm's before fuel and spark are applied. This spinning is often confused with starting. If you were able to read the codes, you would get an "engine didn't start" code.

The possible reasons are:
No spark, no fuel, no compression, improper fuel mixture etc. The same reasons why any other engine doesn't start.

 

So when you try to start, the engine turns over and does not start. Do you get a "check engine" light? No codes?

This suggests the engine ECU is not on the bus or failed.

Bob Wilson

 

That's also what I'm thinking, if you've got a no-start and there really are no codes explaining why.

A Prius engine that spins for a matter of seconds, then stops, doesn't seem the same as a no-start in a conventional car, but that's what it is. If that's confusing your mechanic, you might steer him to one of the threads on this forum where it's explained.

From what's reported I don't see any reason to single out the transaxle for suspicion. In fact, the transaxle is what spins the engine while it is trying to start, and that's happening, so there is an indication that the tranny is at least so far ok.

If you're not able to read ECM codes relating to the no-start, that's a problem on its own; perhaps the ECM is bad, or not securely reconnected to the wiring harness after the swap. There is a diagnostic flowchart in the service manual for many conditions including failure to report codes.

If the mechanic for any reason is trying to figure this out using third-party service literature, it is probably time to blow the $15 on access to the Toyota service manuals, find the appropriate diagnostic flowchart in the engine section of volume 1, and follow the steps in order.

-Chap

 

Time the engine when it is "starting" with a stopwatch.
If it "runs" for only 8 seconds +/- 1 second, it never started, something is wrong, often its P3101 and P3191.
Does the shop have a Prius aware scantool? (Techstream or similar?)
Many generic scanners don't read all prius codes.
If no further information try cleaning out the throttle body and intake manifold.
Disconnect and reconnect the 12V battery then try starting again.

 

Did you ever figure this out? I will pass along a couple of tips in case you haven't.

Of course, as the guys above say check the codes. The check engine light needs to work indicating the ECU can switch it on. Check all the fuses.

You can also check for a spark just like an old conventional car- but you need to remove the coil from the plug, stick an old plug in the coil with coil's wire harness still connected, carefully ground the plug to the engine (bad ground may blow electronics if the spark jumps to low voltage wiring). I also grounded the mounting hole for the little coil pack just to be safe. Get someone to try a start and you should see the spark jumping the plug gap.

Most techs know how to check fuel delivery as well. I figured out an even easier way based on elimination. I know I'll get laughed at or flamed for saying this, but...
When I first got the Prius and was still fixing it up I had this no-start issue at times. So when it did this, I just added propane to the throttle body to see if it would start. Eureka- yes! it started ok, so I knew it was lack of fuel. No fuel pressure gauge, gas mess,etc. Think propane torch turned on LOW with rubber hose attached. No, I'm not suggesting you should do this but it worked for me. In the old days (1979), I think Honda recommended techs use propane similarly to see if the idle mixture was too lean or rich. (Add a little to idling car and it should speed up 50 rpm, indicating a slight lean idle- normal). I think, unconfirmed, that the Prius will shut off fuel flow if it doesn't see some of the sensor parameters in range. My intermittent no start was caused by a simple vacuum hose leak.

Rick

 

Good thinking! Now that you mention it, I remember setting the mixture that way on my 1984 Ford 2.8L too, as instructed in the manual. As I recall it took a larger flow of propane than I could get out of my small hardware-store torch, until I removed the burner tube and orifice from the valve and just fit a rubber hose right to the valve body where the orifice would screw in. With the orifice gone I was able to use the valve to dial in just the right flow of propane.

Putting the orifice back before next use as a torch is highly recommended.

-Chap

 

The funny thing, to me, was when I first tried the propane thing on the Prius; I turned off the propane flow and the car continued to run. I didn't quite know what to make of this at first; but came up with 2 possibilities: not enough airflow through the throttle body (it was coming in via my vacuum leak); or maybe the ECU just shut off the fuel (for safety or to prevent flooding ?).

Rick