My 1990 V6 Sei is finally back on the road

[dcz1643]

My V6 engine has decided to intermittently, do silly things. I took it for a drive today and it stalled as I backed off my drive. It then drove fine for a couple of miles and then at a roundabout, it hiccuped, the engine light came on and then it was fine again. When I got hope I turned it off and restarted it, no engine light. I put the blink tester on it and there are no codes stored.
Later in the day, I had the engine idling and it surged again. I decided to change the fuel filter, as I ordered one and it was on my list of things to do. Unfortunately they didn’t sort the engine but at least it’s done now. Looking at the one I took out, there is a chance it has never been changed! I will find this stupid engine problem eventually. Here are some pics of the old fuel filter.

[Dieselman]

For intermittent engine running issues I would check the crank sensor and connector and in particular, the fuel injection relays on the front of the ECU box.
The relay connector are well known for having poor connection, caused by splayed female spade contacts in the sockets.
Also check the throttle potentiometer is sound and the engine loom connector under the Lhm reservoir, which are known to have poor connections.

It's odd that there are no codes if the engine warning lamp illuminated, as that should have stored one. If power is cut for 10 minutes any codes will reset.

[dcz1643]

Hi, thanks for the check list. I have done everything except the crank sensor and I still need to put my multimeter on the throttle potentiometer but I have given it a good go with Servisol and worked the pot. Things seemed to have improved but again, when I tried to accelerate hard, it hiccuped again, warning light came on but then it was ok again. I drove home, turned the engine off, started it again, no engine light. I rev’d the engine and it took too long for the revs to go back to idle. Onwards and upwards, do you know where the crank sensor is on the V6 auto? Cheers

[Dieselman]

On the bell-housing under the throttle body. The connector is the brown one mounted next to the throttle body.
I doubt it's the crank sensor, otherwise the engine wouldn't run at all.

Lubricate the throttle flap mechanism, check the output of the throttle position sensor, perform a smoke test on the intake and fuel pressure test and check the MAP sensor pipe is neither blocked, or leaking.
Check all vacuum take off ports into the throttle body and intake manifold are clear.
The TPS setting and operation is crucial to acceleration performance, as it momentarily overrides the Lambda sensor to increase fuelling for acceleration.
Check the output is ~0.5v at throttle closed and greater then 4.5v at WOT. The TPS sets base mixture strength.

I doubt it is this, but check the spark output and the distributor rotor a for corrosion.

The throttle and idle compensator should directly control engine revs, so if they are working smoothly, the revs holding up has to be an air leak.

Given the engine management lamp illuminates there should be stored codes.

[dcz1643]

Hi again, still trying to sort my engine issue. Today I tried testing the fuel pressure but I am a bit sketchy about the layout of the system and where I should be taking the pressure reading from. I have attached a photo and I believe the pressure regulator is on the left.
I don’t know what the part is on the right. I do know the main fuel line comes into that part and it is under pressure. I tried teeing in just after the unit on the right, so the reading I got was on the line which feeds the injector rails. I got a reading of 60 psi, which seems rather high. I did check the fuel pump, which seems to be working fine and I did test the output at the pump and it was 70 psi.
I am not sure what I should be getting, or where I should be testing, so any advice would be welcome. Cheers

[Dieselman]

The item on the left is indeed the fuel pressure regulator, which should give an output to the rail of 3 Bar.
The part to the right is the fuel pressure damper, which is there to smooth out pressure pulses caused when the injectors fire.
The injection system on your car batch fires the injectors twice per engine revolution, so creates significant sudden draw from the fuel rail, which in turn momentarily depletes the pressure, hence a small accumulator is installed to maintain constant fuel pressure.

For tests:
Dead head the pump to see it's maximum pressure. It appears you have done this as you recorded 70Psi.
Tee into the fuel pipe before the pressure regulator and see if the pressure is at 3 Bar and maintains that. This also serves as an injector leak down test. If there is any leakage disconnect the FPR return pipe and face it into a clear bottle and turn on the Ign, at which point there should be a single squirt that then stops, with fuel pressure maintained at 3Bar.
If the FPR continues to leak fuel it is faulty, if not and the pressure keeps dropping, one, or more injectors are leaking.

It's worth checking the vacuum pipe to the FPR is sound and it responds to vacuum. Record the pressure reading and unplug the pipe and it should rise when next pressurised.

[dcz1643]

Thanks for this, it will really help me. I felt I was working in the dark, as I didn’t fully understand the fuel system. As you say, I did check the pump directly and it was 70 psi. I also checked the fuel pipe as it came into the engine bay (before the fuel pressure damper and I got 60 psi. I guess there will be some pressure loss as the fuel goes through the filter (which I renewed), so that is probably OK. Now I have this testing information from you, I will go back to it today and see what I get. I just need to keep ruling things out, until I find the problem. Many, many thanks…Derek

[dcz1643]

Fuel pressure update. I did all the tests as recommended by DieselMan and I think everything checks out. The only thing I would say is that the fuel pressure is at 40 psi (measured between the fuel smoothing part and the injector rails), which is a little low. However, the pressure holds and does not drop, so I am thinking this maybe in tolerance? So if I am right about the slightly lower fuel pressure, everything is OK, the fuel pump, the FPR, the vacuum and the injectors. So even though this hasn’t sorted the problem, I think I can eliminate fuel? Cheers…

[Dieselman]

You can test the fuel pressure with the engine running, but if you aren't seeing hot start or only hot running issues, then the fault probably isn't the fuel pressure.
Low fuel pressure not only causes the injectors to spray less fuel per injection pulse, but also causes vapour locks as the petrol boils in the fuel rail. Assuming the stumbling you are seeing is only with a hot engine, it could be the problem and why you aren't seeing any fault codes, as the Ecu has no method of monitoring fuel pressure.
What might be happening is the fuel boils so the injectors can't deliver much, then the Lambda sensor detects lean mixture although all electrical signals are correct. The Lambda sensor reading then causes the Ecu to illuminate the engine management lamp.

Try the fuel pressure with engine running and vacuum connected and disconnected.

How was that reading obtained, engine on/off and vacuum on/off?

My experience is that cars left for some time often have fuel pressure regulator issues, if the pressure is genuinely low at the rail, I would fit a new one, P# 1563A5 / BOSCH 0 280 160 232

For more information on the engine management see the Fenix 3 book in this linked to thread: viewtopic.php?t=10588