Eunos Roadster Mk1 1.6 NA - injector seals replaced and the engine is a lot hotter

Can't really help with specifics for this engine as it's not a model I've owned but I'll throw in some general pointers which may give you some things to think about.

Don't see why correcting the injectors should change the heating, I'd have thought it would be more likely that something else may have been changed as part of the disassembly/assembly process.
How much disassembly was required to reach the injectors, which parts had to be removed? Possibly worth checking back over everything make sure all pipes are tight, not crimped (blocked) and are in the correct place.
Also if any coolant hoses were removed or passages opened this may have introduced air into the system causing an airlock and over heating.
The only other reason I can think of for overheating is lean mixture, did you just change seals in original injectors or have the injectors been changed also?

The area you've outlined on the right is the throttle body, presumably these cars have a stepper motor controlled, idle speed control which may account for the buzzing. This device would normally sit somewhere between the trottle body and the plenum (the bit just under you LH outline), it could be part of the item you can see in your outline bolted to the rear of the plenum with the pipe going to it.
No idea why this should be buzzing with ignition on/engine off.
Does it buzz continuously or just when first turning on? It is quite typical for the stepper motor to be driven out by a fixed number of steps on ECU start up (giving maximum air bypass) an then close up once the engine starts to home in on the correct idle (engine starts at high idle then reduces to correct value), this should only be a short buzz though. If it is only a short buzz this may be correct and you just didn't notice it before.

Hi Jo


With regard to the hot running, as I say I can't really comment on this as I'm not au fait with the specifics of this system but on a generic level I can only see this being caused by cooling system issues (which you seem to have investigated) or lean running which could happen due to an air leak into the plenum (or anywhere beyond the air flow meter - AFM) which I'm assuming sits somewhere ahead of the throttle body. There may be a number of connections to this to things like the brake servo, engine breather and possibly others. If any of these have been left unconnected or even leaking it could cause lean running. I'm assuming being a 1.6 NA this is an early car and hence early EFi system (late '80s/early '90s is infant time for EFi) so possibly doesn't make much use of closed loop running which would attempt to adapt to this and/or OBDII which should throw a warning light if this was occurring.

With regard to the buzzing sound, my understanding is that this starts as soon as you turn on the ignition prior to actually starting the engine and continues until the engine starts (even if you leave it some time), obviously it could continue after that but you would not hear it.
The most obvious cause of this is the idle air control (IAC) although you could try and pin the noise location down with an engine stethoscope or long thin screwdriver held to the ear. I mentioned in my previous post this type of system using a stepper motor, in this case the motor is wound fully open at turn on but will then remain stationary until engine start so any buzzing should cease. However early systems used a different method, they had a valve which was simply open or closed and would be switched on/off very quickly, the ‘on’ time determining how much air is supplied to the engine. Theoretically this could cause a buzz but I would not expect this to be active while the engine was not running and I don't understand how this could be influenced by changing the injector seals . It should be easy to locate this, it will be part of the plenum and will have some wiring going to it. I suspect it is this item.





Are there any wires going to this area? If so you could try disconnecting these (keep them clear of any metallic surfaces), if the buzzing goes away this is the problem area and needs to be investigated, if not look for something similar which does have wiring and test in same way.


Out of interest, what age is the car and can you clarify what you mean by 'injector seals', I'm assuming you mean the O' rings on top and bottom of the injectors or are you talking about an internal seal?

Hi GDCobra,

Thank you again, your replies are great I am learning every time 😊
My car is 1991.

Yes this is correct - my understanding is that this starts as soon as you turn on the ignition prior to actually starting the engine and continues until the engine starts

It was all four lower seals which were replaced and I think one o-ring.

I will have to wait until the weekend for time and daylight to check hoses and wires.

The ECUs were checked around the car and all ok.

Unfortunately my fan has now gone slow and I think this is related to the electrical noise? Very frustrating. Just stumbled on a couple of other forums and they mention the thottle body and it is in that area.
Could it be the PCV Valve / Pipe?
I will try using a screw driver to pinpoint the noise.

A few techy issues but will get photos added tomorrow.

Thank you again, Jo

Evening GDCobra,

Thank you again. Am going back to the garage on Sunday, hoping this will be fixed. Will update you after.

Please see photos. Hope they help.

Have a great Bank Hol weekend.

Thank you for all of the help, Jo

Hi Jo

Those graphics help a lot. Particularly with my understanding of your system generation.
I've labelled up some of the connections below in case you're unsure or for anybody else's benefit.




All of these connections are on the plenum hence downstream of the air flow meter, any leaks hear will let air into the system which will not be metered so no additional fuel added and mixture will be lean.
I'm pretty confident that the item on the side of the plenum (missing in this photo) is the idle air control (IAC) valve as I don't know what else it could be and if it's not the IAC then I've no idea where else it could be. Only reason I'm not absolutely confident is I'd normally expect to see a single hose into the valve with the exit (when the valve is open) going into the plenum.
However on your other graphics this device obviously has 2 hoses attached. It is possible that one of these hoses is an inlet (from upstream of AFM) the other being an outlet piped into the plenum, but it does look like the flange on the plenum has access holes into it. In other words air exits the valve directly into the plenum from the IAC valve.
Having thought about it a possible reason for the 2 hoses is as follows.
One hose goes into the valve body but bypasses the valve and feeds it's air straight through, I'd expect this to be piped to the throttle body in an area where there is a basic idle screw, this would supply sufficient air for the lowest possible idle (on systems I'm familier with this is a passage on the throttle body rather than an external pipe).
The second pipe is controlled by the valve and will supply additional air as/when needed to increase the idle to the required value. I'd expect this to be piped to somewhere between the AFM and the throttle body, possibly on the body itself, that way the air is metered but not controlled by the throttle plate.
I knew I could come up with a plausible story!

Can you trace where those pipes go and maybe get photo's?

I see that the fuel rail is loose, presumably this photo was taken during the injector re-sealing job?
This also indicates that to get to the injectors the PCV hose and IAC valve had to be removed, it doesn't look like there'd be any need to disturb anything else (that's not to say that didn't happen!). For this reason I'd start any investigation in these areas. Bear in mind on a older car it's possible some parts may be working perfectly until disturbed, this is particularly true of flexible hoses and wiring where age has hardened the components so it's very easy to develop a leak or an electrical problem even if very careful. One reason I don't like working on other peoples cars, they tend to blame you for it.

In this graphic you can just see the AFM peeping into the top of the shot.



This gives the game away about the type of system, the quadrant type of shape indicates it is a 'flapper' style meter, as air is allowed in it impinges on a spring loaded door which is held across the system, the greater the air flow (by opening the throttle and increasing RPM) the further the flap opens. This is a mass flow sensor as increasing air density will also open the flap more.
These systems were used in the late '80s early '90s. I'm assuming it is a copy of the Bosch system at the time (I don't recall the name, K-Jetronic or something similar) possibly made under licence from them. I'm sllightly familiar with the V8 version of this so I'm assuming it works the same way.
Although it is described as EFi the E really stands for 'electrical' rather than 'electronic' as I belive this is not a microprocesor controlled system, it simply uses the electrical resistance of various sensors (AFM, RPM, coolant temp, air temp' and possibly others) to control the duty cycle of a square wave output to the injectors, with additional systems to control idle speed and possibly cold running. My knowledge is limited on these systems so apologies if I'm off base with that.
Nothing wrong with that by the way, they do a good job, better than carburettors and the earlier mechanical fuel injection systems.
Due to emmisions regulations fully electronic systems were developed which could read the exhaust output (Lambda) and adjust input accordingly, there are microprocessor based hence 'electronic' (in my vocabulary) and these do become fun! Now it's possible to tweak fuelling with 'maps' so air fuel ratio can be tweaked for specific engine load/RPM conditions and it's also possible to alter the systems programming - What it does and when it does it.

Sorry to go on but someone may be interested.

Here's a wider view image of my early 1990 Mk1 bay which might assist with comparisons etc

Eunosfan said:

Evening GDCobra,

Thank you again. Am going back to the garage on Sunday, hoping this will be fixed. Will update you after.

Please see photos. Hope they help.

Click to expand...

Hi Jo

After my previous post I thought a little more about the IAC valve and maybe I've mislead myself.

Looking at the image I thought the wiring underneath was to this valve.



Having looked over the images I'm now thinking this wiring is actually going to one of the injectors rather than this valve which got me wondering how this can do any sort of job if there is no wiring.
I'm beginning to wonder if this valve is vacuum (or possibly pressure) controlled, possibly one of the hoses has vacuum fed to it which is pulling the valve off its seat and allowing addition (metered) air to flow into the plennum. Perhaps I'm wrong about the function of this valve, it may not be to control idle, it may be to allow higher idle during warm up, the vacuum may be controlled by a heat sensitive valve.

In that case I don't think it takes us any close to your buzzing sound - no electric, no buzz - but could relate to the hot running issue.

Thank you GDCobra,

Your diagram is great thank you.
Some of the photos were taken while at the garage, and others parked up at home.
The AFM was tested and is ok, a 2nd hand one was connected for testing purposes and mine is fine.
The fan has packed up now and the electrical noise is quieter but still constant so I think it is related.
Hopefully will know more tomorrow.
The area framed is where I can hear the noise.
The hoses and wires in this area have been moved and bent a lot while the injectors were being worked on, this could be a potential reason?



Most of the hoses in the below have been disconnected several times




Nice pic boxerdog1.

Hope these help, Jo