89 replies to this topic

[Ozymandias]

I've got a '95 Jap spec SPi.

 

Recently the engine has started to stutter/misfire when the throttle is applied from low revs, especially when the motor is cold, and generally lacks power.

 

The stuttering stops above about 2500 rpm and the problem all but goes away when the engine is up to full running temperature.

 

I have re-set the valve clearances, and the vacuum hoses were replaced about a month ago, so they should be fine - idling is fine and it's not "hunting" for idle level.

 

Could it be something like the inlet temp sensor that has gone and needs replacing? Or could it be a gunked up fuel filter?

 

Many thanks for any advice or thoughts on this!

[IainStallard]

Have you checked the MAP sensor pipes? If one of the lines has broken or an elbow perished, this would be the symptoms. Check the plastic pipes between the inlet manifold to fuel trap, and fuel trap to ECU. It is common for the elbows to snap off and is an easy fix

[Ozymandias]

Have you checked the MAP sensor pipes? If one of the lines has broken or an elbow perished, this would be the symptoms. Check the plastic pipes between the inlet manifold to fuel trap, and fuel trap to ECU. It is common for the elbows to snap off and is an easy fix

 

Thanks Iain! I replaced the hoses very recently, but Sod's Law and all that... I'll give them a check tonight...

[IainStallard]

Might just be a case of one of them falling off, hopefully that's the case as it's the simplest fix!

[spiguy]

My '92 Jap SPi isn't very happy when it is cold. Once up to about 1/4 way on the gauge it cheers up, but I just nurse it until the car warms up anyway. Only takes a few minutes to get up to temperature. If it is absolutely fine once it's warm, then it could be the inlet air temp sensor is faulty and it is defaulting to the fault temperature, whereby the ECU works on the basis of it being 35 DegC. You could check it with a multimeter, as it is basically a resistance which changes with temperature (think it is NTC ie it reduces as it heats up) or if you can get a code reader on it then if it shows a code (can't remember if that logs a code) or if it shows a steady 35 DegC and never changes, then the sensor or it's wiring is suspect.

 

There is also an electrical heater in the base of the inlet manifold (PTC heater) which operates for a few minutes from cold startup, this is supposed to aid driveability on a cold engine. They commonly stop working, which could also contribute to your symptoms. As I say though, if the car runs fine when warm, and it passes emissions tests etc then I wouldn't worry. Depends how bad it is when cold. Mine doesn't splutter or misfire, it's just not very happy and feels a bit gutless until it starts to warm up. I see it as a good way to stop me driving it hard before it's warm. It's like the car is saying "hey, hold on a minute I'm just up! Let me get my shizzle together will you!"

[FlyingScot]

In addition to the points raised I am interested in your comment about the "Stuttering stopping above 2500 rpm" worth checking the throttle position sensor (TPS) and check with a multimeter or code reader than it gives 0.4 idle to close 5.0 on full throttle smoothly and without any erratic readings.

FS

[RooBoonix]

In addition to the points raised I am interested in your comment about the "Stuttering stopping above 2500 rpm" worth checking the throttle position sensor (TPS) and check with a multimeter or code reader than it gives 0.4 idle to close 5.0 on full throttle smoothly and without any erratic readings.

FS

 

Is that volts or ohms? Sorry to but in, it's just I have a similar problem so am following this thread to see what the outcome is

[FlyingScot]

Volts in this case measured when running. Diagnostic code reader will give you this or you will need to back probe the sensor or wiring to read with a multimeter.

FS

[spiguy]

No throttle switch on a '95. The ECU just uses the TPS value to indicate idle demand. All the more important for the TPS to be working correctly as a result.

[Ozymandias]

I think I may have found one of the culprits...!

 

I was having a nose under the bonnet last night to check where the various sensors were and to make sure no wiring was frayed when I noticed that the connectors on one of the hoses that goes across the back of the rocker cover had broken.

 

It's broken where the two hoses are joined to the bulkhead on the top right hand side of the motor (I'll try and get a pic later, my description probably isn't that helpful!).

 

The plastic connector has snapped in two, so I've bodged it temporarily with some syphon tube and insulating tape.

 

I took it for a run last night and it was still stuttering, but on the way to work this morning it's so much better! The odd stutter when accelerating in high gear from low revs, but better.

 

I'm guessing this break has been affecting the advance/retard?

[Ozymandias]

I've attached a couple of pics of the offending broken hose/connector (you can see the syphon tube/insulating tape repair!)

 

It seems that the connector coming off the sensor which the pipe attaches to has broken - does anyone know what the

sensor is?

 

 

 IMG_3814 (800x600).jpg   235.97K   35 downloads

 

 

 

 

 IMG_3815 (800x600).jpg   198.46K   20 downloads

 

[spiguy]

That is your purge valve. There is a pipe which runs to a charcoal canister under the passenger side wing (the pipe that you have taped up). This canister receives fuel vapour from the petrol tank vent, and then every so often under certain driving conditions, the ECU will operate the purge valve. The other pipe from the purge valve runs along the back of the rocker and into the inlet, so that the purged vapour is burned by the engine.

 

They commonly break at that point, mine was broken too. I discovered however that the broken part wasn't really required in that I could remove the broken piece of plastic and then just fit the hose on directly with a pipe clip. I can't remember exactly how that was the case, but I'm sure if you unbolt the purge valve so you can work with it off the car, you'll see what I mean.

 

The effect of this pipe being broken would be that when the valve is opened by the ECU, it could create a sort of vacuum leak, however this would come and go as the ECU modulated the purge valve, and I don't know if it would be a significant vacuum leak or not (depends of the path into the inlet is restricted or not). I seem to remember that the ECU modulates the purge valve under cruising conditions, not accelerating conditions, but I'm not sure.

 

If the valve is not working, or the electrical connection to it is broken, then your broken pipe would have no effect at all on the car's running, as it would never open, and the charcoal canister would just vent to the air through the broken pipe.

 

The fact that you have found this though, is a warning to you to check all the breather hoses as they are a common culprit for splitting, breaking etc and could all in theory give you issues.

[Ozymandias]

That is your purge valve. There is a pipe which runs to a charcoal canister under the passenger side wing (the pipe that you have taped up). This canister receives fuel vapour from the petrol tank vent, and then every so often under certain driving conditions, the ECU will operate the purge valve. The other pipe from the purge valve runs along the back of the rocker and into the inlet, so that the purged vapour is burned by the engine.

 

They commonly break at that point, mine was broken too. I discovered however that the broken part wasn't really required in that I could remove the broken piece of plastic and then just fit the hose on directly with a pipe clip. I can't remember exactly how that was the case, but I'm sure if you unbolt the purge valve so you can work with it off the car, you'll see what I mean.

 

The effect of this pipe being broken would be that when the valve is opened by the ECU, it could create a sort of vacuum leak, however this would come and go as the ECU modulated the purge valve, and I don't know if it would be a significant vacuum leak or not (depends of the path into the inlet is restricted or not). I seem to remember that the ECU modulates the purge valve under cruising conditions, not accelerating conditions, but I'm not sure.

 

If the valve is not working, or the electrical connection to it is broken, then your broken pipe would have no effect at all on the car's running, as it would never open, and the charcoal canister would just vent to the air through the broken pipe.

 

The fact that you have found this though, is a warning to you to check all the breather hoses as they are a common culprit for splitting, breaking etc and could all in theory give you issues.

 

Thanks for this. I've just discovered that the nozzle that's broken - JZX1223 - isn't available any more, so I'm going to have to bodge it somehow!

 

It's weird that the stuttering seems so much better even though the purge valve shouldn't affect the running that much, by what you say - maybe I've inadvertently mended something by checking the sensor wires!

 

I've got a new inlet temp sensor and fuel filter, along with some new plugs that I was going to fit anyway this weekend - I'll give all of the other hoses a good look-at while I'm doing it and see if anything else is beginning to perish.

[FlyingScot]

Here's what spiguy was referring to

"Carbon filter solenoid valve

A CFSV and activated carbon canister will also be employed to aid evaporative emission control. The carbon canister stores fuel vapours until the CFSV is actuated by MEMS. CFSV actuation occurs when the engine temperature is above 70°C, the engine speed above 1500 rpm and the MAP sensor returns less than 30 kPa.
When the CFSV is actuated by MEMS,the valve is modulated on and off,and fuel vapours are drawn into the inlet manifold to be bumt by the engine during normal combustion. So that engine performance will not be affected, the CFSV remains closed during cold engine operation and also during engine idle."

FS

Edited by FlyingScot, 04 June 2015 - 09:35 PM.

[spiguy]

Nice one FS. Oz - take the thing off the car and study it a bit, you will see what I was meaning, that you can remove the broken bit and there is still a bit to attach the hose to.