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Discussion Starter · #1 · (Edited)
Hello. Just wonder if anyone may be able to shed some light on the following.

My fuel pump broke and car wouldn't start.

Put in a replacement and car would start fine from cold but idle much too low and threaten to stall when started with a warm engine. Warm start solution was to gently rev up the engine for about a minute after which it would idle fine.

After all sorts of checks, including the car fuel pressure line non-return check valve, I seem to have resolved the problem by taking out the new pump and assembly and reconfiguring it to the old pump design.

The two pumps are alike though not identical. The old pump (photo 1) pressure line is connected directly to the car fuel line connector, with the return line connected to the ejector. Whereas the new pump (photo 2) pressure line tees off to the ejector prior to reaching the car fuel line connector.

I reconfigured the new pump to be the same as the old one: essentially got rid of the T ejector connection, connected the pressure line from the pump directly to the car fuel line connector and connected the return line to the ejector.

Now the car starts and idles fine whether cold or warm. It's great. But although it now works, I can't figure out why it works — or why it didn't work without reconfigurating the new pump pressure line — , which is somewhat frustrating. As mentioned above, the car pressure line non return valve (number 2 in photo 2) is working.

Any thoughts would be appreciated.
280742
newpump.png
 

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Most likely the check valves in the connectors are the wrong ones or got swapped.
 

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Discussion Starter · #3 ·
"Most likely the check valves in the connectors are the wrong ones or got swapped."

Certainly seems logical. However, neither valves were swapped or wrong, in that they are the same two valves in the same places as they were before the pump was changed.

Non return check valve (with pressure-springed ball) -— pressure line from pump to engine.
280745


Return valve — fuel flow return to pump
280746
 

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Discussion Starter · #5 ·
"What fuel pressures before and after replacement?"

Engine idling, steady 44psi, before and after

Ignition off or on with engine off, zero, or no pressure to read of; i.e no priming of the fuel system without the trigger from the CPS to activate the pump on cranking, which I believe is normal for C900i. Then again, haven't checked engine off pressure since reconfigurating the pump.
 

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After shut-off, it should hold rest pressure.
Around mid-1991(?), they changed the valves, and SAAB supplied new valves with new pumps. At the time, they would run poorly if you mixed up the valves, Their appearance was counter-intuitive.
I remember the confusion at the time, I don't know if this is your problem or not. You could search Service Bulletins (in the stickies) for the running-change and fuller explanation.
 

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Discussion Starter · #7 ·
Thanks a lot for your input, Jim. I looked into the valve change thing and it's seems quite confusing indeed.

In any event, my warm start problem returned, so probably had little if anything to do with the pump configuration. Yesterday the car simply stalled and wouldn't fire up again. Checked a lot of things again this morning after finding all four plugs sooty. In other words, warm start problem seems to be due to it running rich rather than lean. And flooding. Cold start perfect.

No idea why it floods, checked the entire fuel system. All seems good. Am beginning to wonder if the problem is not on account of the new MAF/AMM I put it there. Mine — bosch ending with 017 — was misbehaving. Can't find an equivalent here in the UK so replaced it with a 014 unit for a Mercedes which also comes with a "mixture" adjustment screw. I'd set the resistance to 540 — same as I was running on the 017 — but could be it makes for a much too rich a "mix". Have brought it down to 320 and will see what happens tomorrow to the plugs etc.
 

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You can't swap MAFs like that. Flow:voltage is calibrated per MAF and the ECM relies on that calibration to know what it's doing. Further, the adjustment screw only affects idle mixture and it's a trim on a per-MAF basis - there is no "universal resistance" - the adjustment exists to make up for manufacturing variances and wear.

However, a '90 should be running LH 2.4, which would not have an adjustment screw. LH 2.4 auto-calibrates idle mixture based on previous performance. The additional variable of an adjustment screw would be problematic.

I would get the proper MAF on there before messing with anything else... or potentially causing a bigger lean/rich-related problem.
 

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Discussion Starter · #9 ·
"You can't swap MAFs like that."

You're right. Unfortunately, I haven't been unable to source a Bosch 017 unit. Only Chinese copies that don't fit. My 017 is gone and for now the only option is to use an alternative Bosch AAM. The 014 seemed to work well — the car starts great from cold, feels good and responsive — but turns out it may be running too rich. If so, bad news. May have to try a another MAF again until the right one turns up.

"However, a '90 should be running LH 2.4"

This '90 runs a LH 2.2, no catalytic converter UK variant with 25-pin ECU and adjustable MAF.
 

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Well, that sucks. Hey, at least you don't have to worry about melting your cat with the rich mixture. ;)

In the US there are places that can rebuild MAFs to a very high standard... Surely there is some place somewhere in Europe that can do the same?

Did you call Neobros or 2 Stroke to Turbo?
 

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Discussion Starter · #11 ·
"Well, that sucks."

It sure does.

I haven't looked for places that rebuild MAFs here in the UK; will do but suspect it will be very pricey if I find one.

I checked Neobros and 2stroke but no joy. But thank you for the suggestion. Meanwhile, I took the car on a short ride and it felt great although the idle now settles around the 950-1000rpm and it still idles too low and hunts on warm starts despite my decreasing the MAF resistance. But not if the engine is fired up right away again or within 5 minutes of being switched off. This only happens after 15 to 60 minutes after power down. Odd, suggest pressure problem really. Still, at least it didn't stall, and like you say I needn't worry about the cat.
Guess will lower the MAF some more while on the hunt for the right one.
 

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Discussion Starter · #12 ·
Follow up.

After being reminded of neobrothers and 2stroketurbos — which I'd last checked about a month ago — I checked again just in case and, what do you know, neobrothers had a used 017 MAF which I promptly purchased and should get tomorrow. So thank you for that, jvanabra.

Meanwhile car running with 014 with resistance down to 50 — rich, bad idle on warm starts but running.

To come back to fuel pump and supply. What is this thing highlighted in blue below? Something rattles in there.
280904
 

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Discussion Starter · #13 ·
Ok. It's part #93 18 361: fuel tank ventilation valve. Not much if any information about it online or in manuals, such as should it rattle and air/vapor freely pass through it. Could it all be lost in a black hole over the event horizon.

280939
 

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I fixed a fuel smell under warranty at that valve on a new car once in the mid-'80s.
Other than that, I've never heard of any trouble from what we used to call 'the rollover valve'.
 

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Discussion Starter · #15 ·
"... from what we used to call 'the rollover valve'."

So I presumed on first coming across it, the 'rollover valve'. But isn't the 'rollover valve' meant to be rigged to a line that runs up along the roof and down into the engine bay? This one — as in the diagram above — is part of a foot or so long loop line connected to the fuel tank filler neck.

About warm start problem: got the 017 MAF, car cold starts and runs very well, no more soot on the plugs, but warm start short term variable low idle persists. Since the problem first showed right after the fuel pump change, guess may have to try a different pump to rule the pump out, although the new pump appears to be in good working order.
 

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If it runs at all I wouldn't suspect the fuel pump. The fuel pump just runs at one speed all the time, it wouldn't matter if the car is warm or cold or high rpm or low rpm. The pump does the same thing regardless.

For a low idle, I would suspect the idle valve or a mixture issue... Maybe the NTC sensor?
 

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Discussion Starter · #17 ·
"If it runs at all I wouldn't suspect the fuel pump."

I don't really — it seems illogical. Only the problem started the day I fitted the new pump. Faulty NTC sensor — logical — etc. checked and rechecked. Can't fault anything. Now it's also got its proper MAF back, running out of options and ideas. Becoming a case of 'man' and 'clutching at straw'.
Such as: possible head gasket problem. A very small coolant leak in combustion chamber(s) which only 'leaks' when the engine has been warmed up and then switched off on account of hot pressurized coolant system no longer competing against the greater counterpressure of the running engine. Trace amount of hot coolant pressures/steams its way into hot combustion chamber(s), making hot re-start awkward. As the engine cools unpressurized coolant stops 'leaking', so hardly affects cold starts as system is set to provide more fuel to cold engine, masking the problem. Had something of the sort happen to an old 1970's Triumph once. No idea if it could happen to a C900i, though.
 

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If you have the means to check fuel pressure, it's an easy way to rule out the pump as a culprit for hot start issues.

Are you sure the ignition system is in good shape? Coil/plugs/wires/cap/rotor?
 

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Discussion Starter · #19 ·
"If you have the means to check fuel pressure, it's an easy way to rule out the pump as a culprit for hot start issues."

I did last week, when still running on the 014 MAF; pressure was good and steady 44psi. Unable to check for now as misled coupler/adapter to connect pressure tester gauge to fuel rail. Need to source/make new one.

"Are you sure the ignition system is in good shape? Coil/plugs/wires/cap/rotor?"

Yes. Substituted the lot with a complete good backup set including ignition amplifier and EZK module. Also tried 2 different ECU. No impact, warm start problem remains, like a vapor lock on a fuel system without return line.
 

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I suggest installing the new-style fuel line check valves per Service Information.
 
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