~Opel Lounge~

[021 Chad]

Yeah I was planning to swap the CTS sensor over from my spare motor. I havn't done it yet because from my sleuthing online, the most common symptoms of a dickey Coolant Sensor is poor running when the motor is HOT.
My problem is that it's not running well from a COLD start.

This doesn't rule out the CTS at all, but it did make me start looking elsewhere.I will swap the CTS this weekend and see what happens.

[168 Derek S]

fuel pump?

Idle will be fine but upon a sudden increase in throttle, the pressure drops off. A failed pump is obviously an easy diagnosis, however, a failing pump is difficult. You will usually register the appropriate pressure required to prime for initial start-up thus rendering a pressure reading - useless. It's worth a shot though. Do a search for proper fuel pressure reading prior to cranking. If you haven't already, replace the fuel filter. A clogged filter could very well be the culprit.(but you have changed that) Enough flow for idle but reduced upon acceleration.

I have a spare fuel pump here if needed

[168 Derek S]

[020 Brad]

Maybe try a different idle control valve too, if you have a spare. Cleaning them is easy, but the stepper motor can become faulty after years of pushing sludge around.

[168 Derek S]

I have 2 idle control valves here too, some guy of trade me wants one or maybe them both so let me know if you want one put aside.

[021 Chad]

I doubt it's the idle control valve as it does not explain the missfire when cold, I have about 3 spares floating around . I do have a spare fuel pump, I will try it out, but I do not think it is the culprit either as wouldn't the car be reluctant to perform at all times if the fuel pump was to blame? The Calibra does actually perform very nicely once it has been running for a couple of minutes from cold. Literally in the time it takes me to get 1Km from my house it will be running like clockwork

[127 Gordo]

Did you try replacing the lambda - not sure if it would make much difference, though, as IIRC it's bypassed at cold start.

[021 Chad]

Did you try replacing the lambda - not sure if it would make much difference, though, as IIRC it's bypassed at cold start.

Lambda sensor is 'trim only' on these ECU's. So really only kicks in when cruising to get the economy up. I know because I ran my Vectra for a couple of weeks without the Lambda plugged in as I had not yet machined and welded the boss onto my new headers yet. It didn't make a lick of difference to the running of the motor.

[168 Derek S]

cant help thinking this is a fuel issue.

is there a vacuum tube on the fuel pressure regulator ?

[021 Chad]

I am starting to think this is a fuel pressure issue as well.
This morning I started up and it was running rough as guts, then I stabbed the throttle a couple of times and the revs seemed to stabilize for a while, a few more stabs and it started behaving itself a little better. So I really think that perhaps the fuel pump is not supplying enough pressure, the problem is amplified in the mornings when the fuel pump is struggling to build up the pressure in the fuel rail.
Once the pressure reaches a nominal level, the motor then starts to run normally, but with a healthy fuel pressure the motor would perform even better, the power curve is a little lumpy on hard acceleration now that I'm concentrating on it.

Re: Fuel pressure regulator and vacuum line. A while ago Gordo and I experimented blocking off the vacuum supply to the regulator on our 20XE's, it really only affected fuel pressure at idle and had little or zero affect on the over all running of the motor.

[020 Brad]

My Calibra does something very similar on cold starts and so I have been watching this thread with interest.

Just something to add, when mine is running rough in the morning it smells of unburnt fuel and blows a little black smoke, which as it is also missing I assumed was relating to in ignition issue, however this may also relate to over fueling. This leads me to think perhaps the fuel pressure regulator is "sticking" a little when cold and resulting in an increased fuel pressure, which soon rectifies itself with a bit of a vacuum fluctuation?

[168 Derek S]

I have a used Bosch fuel pump out of a BMW, was using it on my manta to try and get to the bottom of the problem with the 2.0 CIH engine, turned out to be fuel pressure & air flow meter

anyway, the Bosch pump i have is considerably more grunty than a standard pump and it relies on an adjustable fuel pressure regulator / guage for testing.

a manual adjustable fuel reg would be the way to go, I see there are blanking plates available on line for this conversion so it must be an issue or guys just want to run more pressure / bigger injectors

your welcome to borrow both if you want to run a test, I forgot I had them to be honest and probably need to put on trade me at some stage

Derek

[021 Chad]

I was just thinking.
Looking under my Calibra, I noticed that there is a diaphragm valve with a hex head screw adjustment, fitted between the fuel pump and the filter. I have no idea what it's puropse is.
Brad is there a similar valve on your's?

It's almost as if it is a shutoff valve to prevent the fuel tank from draining when one is replacing the fuel filter. Perhaps and this is a long shot, but perhaps the valve is half closed?

[020 Brad]

Like the small thing in the top left of this photo? I haven't had a look under my Calibra, but generally the old bosch units used a crude fuel flow (? ) regulator on the back of them. At least, that's what I've always assumed it to be and I think I've been told it was that over the years. Perhaps a little more investigation is required. I don't think it is a "tap" as such, because the fuel needs to be picked up by the pump anyway, so you don't lose much when changing the filter, only what is in the pump and associated pipes.

[021 Chad]

Thats it, the item top left.
I have been looking for info on this and have not been able to find much, not even sure what key words to use.

What I might end up doing is fiddling with it and seeing what happens
I have a spare on my other Vectra so I doubt any real harm could come of it

I will report back with my findings.