34 replies to this topic

[BritOP94]

 2025-06-24_07.37 engine off throttle test.txt   44.78K   3 downloads

 

Throttle pot test from this morning, one long at full throttle, 3 short ones then another long full one. 

 

You can see the IAC setting itself right at 35 too.

 

Then cold start, erratic idle during which I tried to keep it from stalling with some throttle

 

Tested the MAP lines too, 99-100kPa when I unplug the vac line...

 

Got the manifold out this morning, will check everything from the loom while it's out, replaced the coolant sensor while I'm there. 

 

Is there anything else that can be physically checked/tested? Manifold heater maybe?  

Edited by BritOP94, 24 June 2025 - 06:31 AM.

[BritOP94]

did you have a reset of the ecu already and possibly you gave the system not enough time to stabilize itself

 

2500 viewers up to now and no other ideas???????

 

Once I get the manifold back on the engine I'll try again to do the whole procedure, resetting the ECU, the IACV and try to do so as slowly as possible...

[hungdynasty]

 

 

Got back, plugged the computer: water temp around 90°C, got into closed loop this time, throttle pot 0.56v at idle, but the IACV is still switching 0 and and usually around 49. 

 

I followed Genpop's procedure, then checked the lost motion gap again, but the main problem is still there : it feels like the IACV is just kind of "giving up". when fully warmed up, it will only sit at a higher number than it should, then suddenly drop down to 0 which makes the engine surge and stall if not helped with the throttle. A blip of the throttle brings up the rpms, the IACV follows too and climbs, but when it tries to get back to a stable idle, the IACV drops back down to zero etc... 

Hi, your situation is almost exactly my case back in few months ago,

 

high idling (11xx-12xxrpm) with fully warm engine, map reading normal at around 30 kpa

stepper motor down to 0 position

throttle physically at dead close position, if looking closer, the stepper motor push rod didn't even touch the throttle.

 

What I though is the stepper motor tried to reduce the rpm by reducing steps, all the way to 0. "Normal" map reading was misleading because throttle was dead close with high rpm, when I read my log file I saw something interesting, (please see attachment), there was a short moment the rpm went back to normal(around 900) rpm and the map reading went up to 4x, which is very likely there was a leak in the system. Finally I found that the two gaskets between throttle body-spacer-intake were damaged, I replace the two gaskets and everything back to normal.  

 log 250122 reference.JPG   85.63K   2 downloads

[68+86auto]

To start with, I haven't touched an SPI mini before so I can't go into detail specifically about SPI minis. From what I understand, it is unlikely that the ECU cares much about anything when trying to start. Basically just the temperature to enrich the mixture and the crank angle sensor for timing. Maybe I'm totally wrong though.

 

So why won't it start easily or run properly?

Because you have had it started and it still had issues, I'm going to skip over the battery voltage and starter. So it's a rebuilt engine which I guess has never been run properly before. That means that we could easily be dealing with a mechanical issue such as poorly sealing or poorly adjusted valves. I've seen that before on rebuilt engines where the machine shop assembled the heads. We need to know that the engine has sufficient vacuum to draw the fuel into the combustion chamber. Put a vacuum gauge on a manifold vacuum source and crank. This reading should be somewhere above 6 inHg, my current mini with an old original engine pulls 10.8 inHg at 300 cranking rpm.

Once the engine is running, this reading should be above 16 inHg.

Vacuum diagnostics is a very old method but is very useful.


 

Once we are sure that the engine is mechanically ok, we can move to the ignition and fuel system. These are just some things I'm thinking of:

• Check that it has the correct coil (0.9ohm?).
• Check that the coil gets above 12v.
• Scope the crank angle sensor - for all we know the crank trigger was damaged during the rebuild.
• Check the voltage at the injector

Just like a carbureted engine, starting fluid can be used to see if it's a fuel delivery issue.

[genpop]

@ hungdynasty,

I think you are right, it would be a simple and logical solution, i often think too complicated and forget the simple things.

In this case we would say: Because of all the trees I didn`t see the forest!

I hope we will get good news.

Edited by genpop, 24 June 2025 - 03:37 PM.