Ohc Efi Issue

[Guest Stevieshood]

Dear All,

 

My 2B 2.0i OHC has developed a running issue which has me completely baffled. The idle has increased from ~850 to 1,500rpm, the power is decidedly lacking above 4,000rpm, and it hesitates/misfires badly on acceleration (intermittently though). The EECIV seems to have gone in to some kind of LOS mode as earthing the "octane adjustment" leads doesn't seem to change the static ignition timing (currently 12deg at idle but can be adjusted by moving the dizzy). Also, the idle solenoid drive voltage is fixed, with the idle increasing naturally from 1,300 to 1,500rpm as the engine warms up. According to the gas analyser, CO is 0.3% at (fast) idle, which seems quite low for an 1988 engine without a cat!

 

So far I have checked:

 

Throttle Pot - non-linear in mid-range so replaced with a new one (checked range was 0.5/4.5V at idle/WOT respectively)

 

AFM - seems to produce a nice transient output with 0-5V across it and no sudden dips/spikes. If you unplug, as expected, it stalls.

 

Coolant Temp Sensor - has a resistance that drops as the engine warms up but I haven't any specs to compare it too. If unplugged, the idle speed increases to nearly 2,000rpm.

 

Coil - I replaced this as the old one had a weak spark. It had new leads, dizzy cap, rotor, and plugs when I built it, and it's been firing ok (not rich).

 

ECU - I bought a cheap secondhand unit with the same part number and it made no difference.

 

Fuel Injectors - these were new as the old ones were sticking and wouldn't clean up properly.

 

Wiring - checked every single wire for continuity and earth, and appeared to check out ok.

 

 

As you can imagine, I've wasted a lot of time and started to lose hair over this one! I have double-checked for any leaks from the manifold/intake (although the ECU command seems to be the cause of the high idle because it idles really well if you drive the solenoid with a PSU).

 

My knowledge of these old analogue L-jetronic systems is lacking, so I did a bit of research. I read that the TFI module plays a vital role in transmitting the hall-effect signal. However, I assumed that if moving the dizzy changed the timing, then it was working ok?!

 

Can anyone help me diagnose or point me in the right direction? It would be much appreciated!

 

Steve

[Derek]

Hi Steve,

 

I am at work at the moment but will look later, may have some info that may help.

 

Derek.

[Guest bob13]

My dohc had a similar problem, turned out to be the fuel pump.

[Derek]

Home now. I have sent you a PM but will attach the document here as well.

2.0_injec_1.zip

I found this very useful as it lists the output/resistance of the sensors. If you PM me your email address I can send the originals.

 

I have just overcome a similar problem misfire and it was down to the TFI module earth lead rotting away inside the insulation. The insulation was still attached to the connector but the wire had disappeared so spotting it was impossible. Now I have fixed it I have noticed the spark is much stronger as well.

 

If you have a fuel pressure gauge its no problem to test the fuel pump, but I don't. To see if it was working I removed the return pipe from the return side of the pressure regulator, put on a spare piece of pipe into a container and revved the engine hard. The fuel still ran from the regulator with no bubbles so I was fairly happy the pump was supplying enough pressure.

 

Using a spare dizzy I have tested the system with an electric drill on the dizzy shaft. Spinning it up fires the injectors so you can hear a sticking one. It will also show if the spark weakens under load. Using this method I found (with a lot of help from the forum) a previous problem I had where the throttle position sensor was duff.

[Guest Stevieshood]

Thanks Derek - that article is really useful!! I've PM'd my e-mail address....

 

It was interesting that as I went around each system looking for the fault, I found that some of components were not in the best of health. Hence, I have replaced the injectors, TPS, coil, and fuel pump with a similiar uprated Bosch item (basically a non-genuine Sierra Cosworth one). On that basis, I'm hoping there are no fuel delivery issues.

 

Replacing the TPS and coil has improved the misfire under acceleration but not eradicated it - so I will check the TFI module as you said. It still baffles me why the ECU is demanding a high idle and it's running lean. I would have thought the coolant temp sensor would have caused it to run rich when warm, but I can check the voltage now I have its spec. I guess it could be lean only within the parameters of the fast idle CO check and ok with a bit of load on it?

 

Steve

[Snapperpaul]

Just my halfpence but do check for air leaks, unmetered air, i.e air leaks beyond the air mass meter will cause problems.

[Guest peter2b2002]

as snapperpaul says , my efi played around like yours, I had cracks in the convoluted pipe between the air flow meter and manifold, I had to stretch the pipe before I could see the cracks, I used screen seal to fix the problem(4 years ago) still going strong.

peter2b