Re: [DML] D not running well (but not mine)

["Walter" <Whalt@xxxx>]

> What its doing...
> Starts up right away, but then idles very rough, but will eventually
> smooth out.
> Any throttle movement will almost kill the car. There were a few
> times I could get it to about 4500, but usually it wouldn't go past
> 1800 no matter how well I played with the throttle.

Jim,

I had these symptoms on my car before.

Twice it was caused by the lambda system not working (once due to the lambda
relay and once due to a corroded electrical connection at the frequency
valve itself.) Check if the valve is buzzing like it does on your car.

Once it was caused by a bad electrical connection to the CPR. When
electricity doesn't get to the CPR (or the CPR doesn't respond to it) then
any attempt at cold acceleration is counter-productive.

> There seems to be an apparent exhaust leak on the passenger side, most
> likely the manifold gasket, the owner said it wasn't this loud before.

This may make the engine noisy, but it shouldn't contribute to any
acceleration problems. If anything, it should help the engine breathe
better.

> What I checked...
> Swapped RPM and LAMBDA relays from my car, no avail.

If the engine runs at all, then it couldn't be the RPM relay. This only
switches on the fuel pump. A dead Lambda relay will stop the frequency
valve from working, so a better test is to listen to see if you can tell if
the frequency valve is buzzing.

> Did some unplugging and plugging back in of electricals for CPR, Cold
> start valve, frequency valve, and idle motor, everything acted as it
> should.

Did you check the plugs/sockets for corrosion? I think it is prudent to
pack these with dielectric grease to keep water out of them. It has been a
problem on my car before.

> Tamper-Proof plug is missing.

Plug this hole before you try anything else. It doesn't need to look
pretty -- just find something that blocks air movement through this hole.
Even a bolt covered with duct tape will suffice for temporary use. This
vacuum leak may contribute to the problem, but it sounds like the engine has
something more wrong with it than a vacuum leak here.

> My theory...
> The owner says this happened very suddenly. He drove it to work one
> afternoon, all was good. When he started it up to go home, this was
> happening.

It is possible that whoever removed the tamper-proof plug either forgot to
put it back or stuck a homemade replacement in there that fell out. Check
around the adjustment hole to see if you find the plug or a homemade one
laying on top of the engine.

>I also suspect that the engine could
> have heated up just enough after being shut off, to break some kind of
> seal on the exhaust manifold. With this leak now there, the change in
> backpressure has thrown the fuel adjustment way out of whack.

I strongly disagree with this. I agree that a change in backpressure will
have a small effect on fuel adjustment, but not enough to produce the
symptoms that you describe.

> However...
> About a month ago, I was messing around with my exhaust system, and
> ended up with a fairly massive leak at the front seal for the CAT.
> The engine idle and reved fine (just a helluva lot louder) but under
> load, it would shake VERY violently. I somehow cured this buy
> shooting between 30mph and 60mph entirely in 2nd gear 3 times at
> wide-open-throttle, keeping it in gear when coasting back down to 30.

It sounds like the hard acceleration may have worked a clog out of the fuel
system -- maybe something blocking one of the injectors? Maybe your CAT is
internally damaged and the hard acceleration shook or blew a restriction out
of the way. Maybe a restriction in the CAT contributed to the leaky front
seal.

> Now I still had the leak, but the engine was perfectly smooth at all
> throttles at all speeds in every gear. Somehow somthing must have
> compensated. When I got the leak sealed up, there was no change in
> engine operation. It would have been nice to try this in his car, but
> we really couldn't get the D faster than 20mph.

That sounds pathetic. Plug the vacuum leak! And then see what you get.

> The Questions...
> I am suspecting the reason for this is because his fuel adjustment may
> have been out of whack in the first place, but was just good enough so
> the engine would run fine under normal condions. And now that they're
> not normal, it just can't do it. How close am I?

There is no telling what a previous mechanic may have done. If the owner
indicated that the car suddenly got worse 1000 miles later, than I assume
the mechanic didn't screw up the adjustments too bad. One thing to check
for sure is if any of the idle adjustment screws have been backed out.
(They all should be lightly seated.) If so, then be on the lookout for
similar blunders.

> Any other
> suggesions? Would you recommend fixing the exhaust leak first, or
> fine-tuning the fuel adjustment?

Ignore the exhaust leak for now. It shouldn't have a significant effect on
engine performance. I wouldn't expect the fuel adjustment to be too far out
considering that the car was running okay before. To check the fuel
adjustment properly you need an exhaust gas analyzer. Eventually this
should be done.

> It seems this post has turned out to be longer than anticipated, but
> at least its detailed! Thanks for any advise.

Cool. I tend to neglect my duties in favor of playing with DeLoreans, so
this contributes to my delinquency. :)

Walt Tampa, FL