89 4-cyl; no power at low RPM

Problem: Car has little power at low RPM, but as the RPMs climb the
power is fine. Its almost like one should rev the engine before
letting out on the clutch in order to get the car to take off from a
stand still. Any ideas what could be the problem?

Background: I've been helping a friend get his 89 Mustang four-
clyinder car running again so that he can save money due to higher gas
prices and a recent move to the country and much longer drive into
work. This low-RPM problem remains from when he first gave up on the
car (and let it sit for a few years because one day it wouldn't
start). We've done the standard tune up (plugs, dist. cap and rotor,
timming, etc.) and done OK with getting it to start fine. No engine
codes have registered (all clear except for code 67...neutral circuit -
when actually the car is in gear). Now I'm at a loss for the problem
of no power at low RPM. What factors should I consider and look
into?

Thanks,

dalemstevens wrote:
> Problem: Car has little power at low RPM, but as the RPMs climb the
> power is fine. Its almost like one should rev the engine before
> letting out on the clutch in order to get the car to take off from a
> stand still. Any ideas what could be the problem?
>
> Background: I've been helping a friend get his 89 Mustang four-
> clyinder car running again so that he can save money due to higher gas
> prices and a recent move to the country and much longer drive into
> work. This low-RPM problem remains from when he first gave up on the
> car (and let it sit for a few years because one day it wouldn't
> start). We've done the standard tune up (plugs, dist. cap and rotor,
> timming, etc.) and done OK with getting it to start fine. No engine
> codes have registered (all clear except for code 67...neutral circuit -
> when actually the car is in gear). Now I'm at a loss for the problem
> of no power at low RPM. What factors should I consider and look
> into?
>
> Thanks,


First off, I don't know this specific engine.

In general, I would try to look at ignition advance at part throttle.
Does the distributor have a vacuum can on the side? That would normally
give you an initial kick in the advance just as you begin pushing on the
gas pedal, so the engine would accelerate from idle. It also allows
higher ignition advance at cruising speeds, with small throttle
openings. If the diaphragm inside the can is leaking, or if the hose
connected to it has a leak somewhere, it won't give you that extra
advance and the engine won't respond well to throttle.

Also make sure all moving parts inside the distributor body are clean
and lubricated, and move well without binding. This goes for the
centrifugal weight mechanism parts too. If those are binding, the engine
won't see enough ignition advance.

To verify either the vacuum advance or the centrifugal advance
operation, use a strobe light timing gun and observe the timing changes
when the engine is running. Repeated very small throttle openings should
result in instant ignition jumps (vacuum advance).
The centrifugal advance operation can be checked with the vacuum hose
disconnected and plugged. If you get no change in timing regardless of
engine rpm, then the centrifugal mechanism is not working.

You can also try to suck on the vacuum can hose to try to detect leaks.
You should be able to suck a vacuum in the hose, and block the hose
opening with your tongue... it should stay stuck to the hose, meaning
the vac unit is able to maintain vacuum with zero leaks.
You can also buy an inexpensive manual vac pump from most auto parts
stores, if you don't like getting your mouth dirty

Another problem may be incorrect mixture. Troubleshooting and fixing
this may get a bit more complicated and vehicle specific, so I won't get
into that here.

Jan

On Apr 13, 4:21*pm, dalemstevens > wrote:
> Problem: Car has little power at low RPM, but as the RPMs climb the
> power is fine. *Its almost like one should rev the engine before
> letting out on the clutch in order to get the car to take off from a
> stand still. Any ideas what could be the problem?
>
> Background: I've been helping a friend get his 89 Mustang four-
> clyinder car running again so that he can save money due to higher gas
> prices and a recent move to the country and much longer drive into
> work. *This low-RPM problem remains from when he first gave up on the
> car (and let it sit for a few years because one day it wouldn't
> start). * We've done the standard tune up (plugs, dist. cap and rotor,
> timming, etc.) and done OK with getting it to start fine. *No engine
> codes have registered (all clear except for code 67...neutral circuit -
> when actually the car is in gear). *Now I'm at a loss for the problem
> of no power at low RPM. * What factors should I consider and look
> into?
>
> Thanks,

Like Jan, I don't know the 4 cyl engine that well. Everytime I fill
up, I thiink your friend has the right idea - he / she gets the
Mustang experience with a little less bite at the pump. :-)
Anyway, on the 8 cylinder, I'd look at the idle air control, if
present on that motor, and possibly the TPS. I heard both suspected
in low idle driveability concerns, although Jan's vacuum ideas are at
least as good. The IAC gets gummed up over time, and is an expensive
piece to replace, but 20 mins with a can of carb / throttle cleaner
has NEVER failed me.

Jan Andersson > wrote in news:66fa87F2kbrhjU1
@mid.individual.net:

> In general, I would try to look at ignition advance at part throttle.
> Does the distributor have a vacuum can on the side?

It's an '89. All it's controls are going to be electronic.

I am going to help my friend tomorrow, we have two different service
manuals and hope to check out sensors and find one that may be at
fault. The spark advance is controlled by a TFI electronic control (I
replied initially to this posting that fact, but it never showed up),
and I've read that it can have problems with heat. I plan to try
quick cool, etc to isolate. What my friend has told me is that the
car does run fine for about 5 minutes when cold. Fine, but why would
problems with TFI getting hot, be apparent only at low RPM, what would
be the symptoms be for a heat failing TFI - no spark advance at all-?
How would it work fine at higher RPM and not low RPM if TFI is
failing? It would seem to me that something is giving the computer
control module band info at for low RPM and I will be checking the TPS
for one. Any other suggestions, opinions is appreciated.

Thanks

On Apr 13, 4:21*pm, dalemstevens > wrote:
> Problem: Car has little power at low RPM, but as the RPMs climb the
> power is fine. *Its almost like one should rev the engine before
> letting out on the clutch in order to get the car to take off from a
> stand still. Any ideas what could be the problem?
>

"dalemstevens" > wrote in message
...
> I am going to help my friend tomorrow, we have two different service
> manuals and hope to check out sensors and find one that may be at
> fault. The spark advance is controlled by a TFI electronic control (I
> replied initially to this posting that fact, but it never showed up),
> and I've read that it can have problems with heat. I plan to try
> quick cool, etc to isolate. What my friend has told me is that the
> car does run fine for about 5 minutes when cold. Fine, but why would
> problems with TFI getting hot, be apparent only at low RPM, what would
> be the symptoms be for a heat failing TFI - no spark advance at all-?
> How would it work fine at higher RPM and not low RPM if TFI is
> failing? It would seem to me that something is giving the computer
> control module band info at for low RPM and I will be checking the TPS
> for one. Any other suggestions, opinions is appreciated.
>
> Thanks

When the TFI overheated on my '89 four-banger, it would usually just
suddenly and instantly shut the car down. More often, it would not allow a
restart of a warmed-up engine, until it had had a half hour or so to cool
down. This doesn't sound like your problem.

I would take Jim C's approach and start first by cleaning the air intake
passages. The MAF sensor and idle air bypass are both easy enough to clean
out (probably a LOT of gunk in that IAB, if it's never been touched).

See http://www.muscularmustangs.com/iac.php for a pretty good overview.

dwight