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'88 325i No Start, Thorough Diagnosis

Discussion in 'E30 (1984-1993)' started by openwheeler3, Dec 29, 2009.

    openwheeler3 guest

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    I recently purchased an '88 325i as a project car. It ran fine until one day I was putting it through its paces. The first symptom was when I was at full throttle at about 4,500 rpm and the engine hesitated for a second as if it was starved of fuel. I then drove it home and before I pulled into my driveway, the engine stalled. I restarted the engine and pulled into the driveway and turned it off; the car has not started since. The engine turns over when attempting to start but it does not catch. I have done a full diagnosis. I replaced the fuel pump relay and main relay and the fuel pressure regulator. The fuel pump works (I jumped the terminals and fuel delivery rate is correct). The spark plugs spark, the fuel injectors open (manually tested using the ECU harness), and fuel both enters and exits the fuel rail. The crank position sensor works and I replaced the ECU as a last ditch attempt to solve the problem. I tested the ECU wiring harness to ensure that the CPS and injector signals are being received. I also checked the timing belt to make sure everything was properly aligned. At this point, I am out of any diagnosis ideas.

    If anyone has any thoughts they will be greatly appreciated.
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    epbrown01

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    I'm not that familiar with the E30 (though I'm looking into becoming so :)), but non-start problems are typically related to spark, fuel, and air. You've confirmed the first two - no chance you've got a clogged air filter or intake, or clogged exhaust?
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    CRKrieger

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    Epbrown could be on the right track. A clogged exhaust can be caused by a catalytic converter failure that allows the ribbon substrate to get blown downstream, blocking the system. If gases can't get out, gases can't get in. I had this exact thing happen to an Audi Quattro I once owned. Symptoms were quite similar.

    The other possibility is a gross vacuum leak. I would check the big rubber intake boot for tears and cracks.

    openwheeler3 guest

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    Thanks for your input. I did check the intake side of the equation. The air flow sensor is working properly and I also attempted a start with the rubber intake boot disconnected (I know this sounds bad, but I'm desperate). No change occurred. The intake boot itself is in good shape.

    How would I check check for those exhaust problems?
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    MGarrison

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    Duct tape a vacuum to the exhaust and, holding the throttle-body flap open, see if a piece of paper will stay in place over the throttle-body opening? Or feel for air movement? Detach or loosen the converter from the manifold and see if it will start? If you do that, you could perhaps blow air into the converter. I'm picturing a large mass of Rube-Goldberg-ed duct tape.... hope you figure it out!

    openwheeler3 guest

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    I checked the exhaust today by taping some paper towels over the muffler and they pulsated while cranking the engine, meaning that the exhaust system is clear.

    While looking in the engine compartment, I did notice the induction sensor connected to the number 6 spark plug wire has broken wire housing and possible damage to the wires inside. Could this affect engine starting?
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    MGarrison

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    All Please Rise, and turn your Bentley Manuals to page 24 of Section 5 (Ignition), and under section 5.3, see "Note-"

    On 325i(is) and 1988 through 1990 325 models, there is an inductive pickup on the no. 6 spark plug wire. This sensor signal is used to sequence the fuel injectors. See FUEL SYSTEM for more information.

    Please turn your hymnals, err, manuals to page 49, table m, Section 6 (FUEL SYSTEM) and refer to "Cylinder identification sensor" to test terminals 8 & 31 on a 55-point motronic connector for less than 1.0 ohm resistance.

    I would suspect that if the motronic isn't getting the appropriate input it's not going to know when to trigger the injectors, and can only guess that the default is to not run the injectors in the absence of cylinder identification.

    openwheeler3 guest

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    I checked the resistance of those connectors and my multimeter showed 0.3 ohms, meaning that this circuit works properly. Any idea what else controls fuel injection?
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    MGarrison

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    This would seem unlikely to me, but is it possible that some type of debris clogged multiple injectors in one instance? When you swapped ECU's, did you ensure the replacement ECU had the same number on the (presumably green) label - I think on the shorter number (1 digit, 3 digits, 3 digits) the last 3 digits need to be the same.

    I presume you have the E30 Bentley manual having done that much testing, which covers the motronic system in some detail in the latter half of section 6. Our resident mechanic Moosehead (Paul) may have some more insight if he catches this thread, I would presume he's afk through the holidays here.

    I can't offer much insight beyond what the Bentley manual provides, as I'm hardly a motronic expert - it seems as if you've been reasonably thorough, although this obviously doesn't seem to be something relatively straightforward.

    Does your car have the multi-funtion on-board computer? If so, I wonder if there's some way it could have a fault from the 'code' security function, which keeps the car from starting, I think by cutting fuel delivery, possibly via the fuel relay, once you've entered a code. Anyway, you might try unplugging the OBC, on the off-chance. Obviously a moot point if there's no OBC.

    Try the other BMW forums too, and also consider calling any of the club Technical Service Advisors (listed in the back of the Roundel).

    openwheeler3 guest

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    First, I want to thank everyone for their advice.

    Mgarrison: to your last post, The ECU numbers do match and I have been using the Bentley manual the entire time. I tried detaching the OBC, but it had no effect. I guess it is possible that all of the injectors are clogged, but I did use techron injector cleaner a few weeks before the problem arose. I searched all over the internet for similar problems and have found nothing that points out a solution.

    I am going to order the Bosch fuel injection manual from Bavarian Auto for more detailed descriptions of the motronic system. Essentially, I need to find all of the factors that would prevent the ECU from opening the fuel injectors.
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    granthr

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    Sorry I don't have any advice regarding your specific problem. But now might be the time to find a reliable independent BMW mechanic in your area. It could very possibly be something very simple and they would be able to find it quickly. Here is a good place to find one, http://www.bimrs.org/ Good luck.

    callmasterIV guest

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    not sure if you could solve that, but theres 2 plugs around the valve cover, passenger side , bracketed to the valve cover. they like to..vaporize.
    mine are cable-tie secured at the moment, and soemstage ill get new plugs in. if theyre loose, nothing is happening, besides engine turning.

    like, hit a little bump on the road, so it goes stally whilst driving, 4500 sounds like acceleration, ...and hit one on the driveway to get em fully loose..?

    lugerhead guest

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    May have something for you. There is a electrical plug below the intake that connects the injector wiring harness to the main harness that then goes back to the ECU. I had a 89 325 years back that this connector got really corroded. 12 volts comes to the injectors through this connector, and the ECU grounds if I remember 3 of them at a time to run the engine. Long story short if there is any contact problem in the connector the injectors will not ground to complete the circuit or they could not be getting enough current to run. The temp sender and sensor also goes through this same connector. Good luck.
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    Ricardo Epps

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    You may want to look at the crank sensor. My 325 would start while cold and when warm would not start.Having tried many things, took to a shoop that found it was the crank sensor.

    Good luck

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