Boerge

Update on the 5000 s NF motor..
Still not running right.

I have new:

Spark plugs, dist rotor, spark plug wires, ISV (Brand new, can be blown through), MFTS, Water temp sensor (2 wire, same location as MFTS).Some of the vacuum hoses have been fixed/replaced

O2 sensor seems new from previous owner, but cannot guarantee.

I have checked:
Tried with a new computer(Jetronic) to replace the one in passenger footwell, timing belt location and dist location, tried without CAT mounted in exhaust, have checked CO and HC with analyzer, adjusted CO screw very slightly. This didn't really affect anything, but CO was good.


Car still doesn't run right. Runs best for 1 minute when cold, in the morning. After one minute, starts to act up, press some throttle will result in car stumbling, full throttle will however force it to accelerate, although very slow and rough running.

1 minute of that crap, and suddenly it decides to run right, this is felt immediately. Same thing every morning. I know where on my route to work it will act up and start to work again.

When I say it runs right, this means "not rough", but still car feels weak, revs slowly, slow throttle response, not clean power when full throttle, like if timing is wrong or something.

So I use the car like this everyday.

If car is warm, I shut car off for 5 minutes, then it acts up again when I start the car. This is evident in rough idle, and any throttle will result in pops under the hood (Backfire?).

After approx 1 minute, if left idling, the idle changes tone very noticeably, and it works like it used to before I stopped it again. Seems right, but weak and slow revving.

If I shut car down when warm and immediately starts it again, it does not act up like that.

So my quest in getting it to run right continues.
It is me vs the bloody car now.

What more sensors apart from MTFS and 2 wire water temp sensor at same location, gives input to the ECU?
Can this be fuel pressure related? I have a DP unit on the fuel dist, can this be broken?

Next step is to change intake gasket and injectors.
Any more help is appreciated.

regards
Boerge

shortyq

I've been reading many of these CIS issues over the last few years here... And found it's tough, even as a 20 year seasoned CIS guy, to do a lot of diagnostics without fuel pressures.

The easiest thing to do is concentrate on vacuum leaks, the intake manifold gasket is one of the harder to isolate.

That said, sounds like a/vacuum leaks to me. If CO is not affected by changes in adjustment, you most likely have an air leak somewhere. IME, once running, if you pull the oil cap off, the car should stall. If it continues to run, you have other problems. Also, make sure your PCV routing is not collapsed and/or cracked/leaking.

Fuel pressures can tell you a lot of things about the fueling system. Sounds premature for now....

HTH and my .02

Scott J

dkarten

I suspect the fuel injectors, I had one bad injector that when replaced solved some issues, but eventually I replaced the other 4, engine runs very sweetly now

shortyq

If you are lucky and a tight motor with a properly functioning idle stabilizer, it will stumble and recover. My bet is there is no difference with the oil cap removed = problem.

Could be injectors, but that should show up in a fuel system test (leaking injectors) and/or a flow rate/pattern test. At 250bucks minimum = should be more than suspicion that gets you to that point.

Scott J

dkarten

shorty, I have a 100Q & a 5KQ, when the 100 cap is removed it stalls immediately, when the 5K oil cap is removed there is no change, I spent a lot of time chasing a non existent vacuum leak on the 5K because I thought it was supposed to stall but then someone responded to my post & informed me that not all CIS systems stall on cap removal, the turbo 5K does stall, but it would seem the non turbo does not, I will stand corrected if someone states otherwise & can help me find the problem, but my 5K runs sweet since I replaced the injectors, note that BEFORE I replaced injectors I replaced injector o-rings but my problem was clogged injectors & it would exhibit symptoms similar to what Boerge has, new injectors eliminated the problem, best price was at World Immpex, I think under $50 each
hth

AudiSpaulding

but, for injectors I seriously recommend you check out my how-to. Pick up the Mercedes injectors I list (like 20 bucks a piece from autohausaz) and swap the air caps over, etc...

The whole job is overall pretty straightforward, and I noticed my car was running MUCH smoother afterward.<ul><li><a href="http://www.justfourrings.com/phpBB2/viewtopic.php?p=19111">http://www.justfourrings.com/phpBB2/viewtopic.php?p=19111</a</li></ul>

shortyq

On a properly tuned CIS car, the oil cap removed will make a difference to the running of the motor. This is because the PCV routing to the airbox affects proper CO. The reason it doesn't always *stall* is because the main crankcase ventilation vacuum on the 5k (non turbo) goes below the airflap, on the turbo CIS cars it has a restrictor and goes above the airflap.

That said, since CO is affected by air leaks, the proper procedure is to disconnect and plug crankcase vent hoses. As PCV in the non turbo 5k is also routed to the idle stabilization circuit, opening the oil cap to vacuum should affect idle stabilization. IME with these (non turbo CIS) systems, a really good tight non turbo CIS car with a clean PCV system will stumble and recover that leak. A CIS car with other issues will just stall, because the Idle stabilizer/O2 freq valve can't compensate for that additional leak. If the PCV valve is clogged, or the PCV vent lines are clogged, your assessment would be correct, as the air leak has been effectively plugged? BTST too.

WRT your injector call, I won't say it's not true. I do say that to spend 250USD without knowing that's the issue, sounds expensive to me. Further, since his HC and CO appears ok with exhaust analyzer, I'm not inclined to believe that without testing of those components. IME, bad injectors will cause HC and CO to be out of spec, because the 02 sensor circuit is not able to compensate for those bad injectors.

Again, I'm a fan of fuel guages for diagnostics here. Bad/leaking injectors will fail the residual pressure check, and a quick pattern check requires only a beaker, a 3mm allen and bypassing the fuel pump relay. In fact, you can do the spray/volume ck, run the pump a few seconds more, empty the beaker, come back a few minutes later to ck for leaky injectors.

Me, I'd be cking the fuel pressure regulator (diaphram). IME with the older CIS cars, if that diaphram leaks it sucks fuel into the CIS boot. Then I'd be hooking up fuel guages.

HTH and my .02

Scott J

dkarten

I can only relate my personal experience, I am curious how other non turbo NF engines react when cap is removed, anyone else like to share experience?

Boerge

Thanks for all help so far. I am not giving up until it runs right.
Was outside with idling car, removed oil cap, absolutely no change in idle or sound.Tried many times.
Maybe that can give some input to the VAC leak discussion.
The fuel pressure membrane, is that mounted on the side of the fuel dist, it can be replaced, I might find one at the breaker.
WRT injectors, I have a set of new ones from my old A5000KTQ, I believe they are the same and will change.
Any more help is great, you guys seem to know a lot.
Regards
Boerge

5000Q86

try adding some drygas to the fuel and some high grade premium fuel from a very busy station. if you use regular or plus fuel, it will misfire and run like a bag of crap. also, if you go to a not so busy station, the gas has time to sit and collect moisture in the tanks underground.

it could very well be a vacuum leak, but the easiest thing to do is try some different gas or add drygas.

good luck!!
Eric