seeking guidance on an 88 ranger 2.9 that’s idling erratically and it won’t accelerate beyond 2000rpm. this issue started after my mechanic replaced AC compressor, oil pan gasket, power steering, spark plugs and distributor cap and rotor. he couldn’t figure out why but suggested it could possibly be a faulty distributor cap. he has since moved out of the country. i decided it was time i get some working knowledge of how cars operate, but dang, had no idea i’d spiral this far into the abyss.

i’ve since replaced the distributor cap, spark plug wires, MAP, TPS sensor, temperature sensor, fuel filter, fuel pump, cleaned the throttle body, checked for air leaks, added fuel treatment, etc. and yet the problem persists.

when i run the engine with the tps unplugged, it seems to steady the idle though i still can’t accelerate past 2000rpm. to the latter, when i accelerate at the throttle, i’m able to get it past 2000rpm but the engine doesn’t like it.

no check engine light and it starts right up without hesitation. another mechanic (retired) i recently met suggested replacing the catalytic converter. wanting to check in with ranger folks here for guidance before i fall further into oblivion.

also wanting to know if this year and model requires a dual cat system; the truck currently has dual cats on a single muffler. i see single (CARB) cats hovering around $400, and a dual for over $1000.

i’d appreciate anyone out there who got ideas on solving this puzzler!

 

Welcome to the forum

Limited RPMs can be clogged exhaust, usually broken apart Cat internally, tap on it with wooden stick or rubber mallet to see if it rattles, engine off
You can test for this with vacuum gauge

Cat replacement is based on the amount of emissions it can process and pass "the test", 2 smaller Cats may fit better than one larger Cat, so manufactures choice at the time the vehicle was made
Calif likes to see factory setup on any emission part replacement, but on a 1988 you can make a point of "no longer available" and use the single larger(cheaper) Cat
IF(big if) thats is the problem

But this shouldn't effect idle, just higher RPMs because exhaust can't get out so engine can't pull in new air/fuel mix

No codes means it not a sensor issue as they are monitored
For idle issues check PCV Valve, its a variable planned vacuum leak

Test engine with vacuum gauge, cheap tool, and one of the better tools to have available, easy to use and lots of information on what things means

 

thanks ron! i forgot to mention that i replaced the pcv valve. i’ll knock the cat to see if it rattles—i should add that there does appear to be a rattling when i accelerate. unsure the origin.

just got a vacuum gauge and i’ll test and report back.

 

Engine is a self powered air pump, so if you want to test a pump you use a Pressure gauge, in this case an "anti-pressure" gauge, lol

Gasoline engine vacuum is universal, from 1 cylinder to V12 it only changes with outside pressure, i.e. elevation above sea level
And no matter how much electronics "they" add to the outside, the mechanics of an engine all stay the same, old air out, new air with fuel added in, is how it works, so a vacuum gauge can tell you a lot about an engine

 

Was having the same problem but my engine on a 2002 3.0 threw a misfire code. P0304 to be exact. However I think due to the misfire it started to break down the internals of the cat. Doesn’t seem like a terribly hard replacement though. However I’ve no experience in the matter. Good luck to ya!

 

I replaced the PCV valve, which saw a positive change in engine performance—still idled rough but less erratic. I was also able to rev past 2000rpm at the pedal although engine still struggles to push past 2000rpm.

admittedly, i have no idea which vacuum line to test, so i started with the pvc hose. it turns out the hose had several cracks. I replaced it, bolted the muffler back onto the catalytic (previously took it off under advisement to test the unit), remounted the hose from filter to throttle, and in doing so, the engine went back to idle erratically and i couldn’t rev past 2000rpm. any idea as to what caused this reversion and what my next steps are?

 

Reads like MAP sensor issue or Clogged Cat

You need to get/use a vacuum gauge to test engine, they run about $10
You connect it to a smaller vacuum port on the intake
Follow the larger hose on power brake booster over to upper intake, it connects to the "Vacuum Manifold" and it has several smaller ports, one should just have a cap on it, remove the cap and hook up Vacuum Gauge's hose to that port
Start the engine

Idling engine should have 18-21" of vacuum, if under 2,000ft elevation(i.e. in the mountains)
Lower means engine issue
Raise RPMs to about 1,500, doesn't have to be exact, hold RPMs steady and vacuum should be steady, if vacuum is slowly dropping you have a Clogged exhaust could be Cat converter

MAP sensor is mounted on the firewall, it has a 3 wire connector and a Vacuum hose, check that vacuum hose, needs to be air tight and connected to upper intake
Unplug connector, make sure its clean and dry inside, reconnect
You can Google: Test Ford MAP sensor
Watch the videos

 

thank you so much ron! i’ll give it a test. could it possibly be an exhaust leak at the muffler that’s causing the misfire and rough idle? i ask bc it’s rusted through at various points, and i wonder if thats the reason it runs worse when connected to the cat.

also, i replaced the MAP about 6 months.

 

No, only an exhaust leak at the exhaust manifolds can cause running issues

 

ran the test at the vacuum manifold; on start, needle jumps all over the place, settles at about 20, dips to under 15, jumps to 25, settled back to 20, repeating this cycle. tried raising rpm to 1500, but could not keep it steady there, engine behaving erratically. when i released the gas pedal, the rpm would shoot up then dips to about 800rpm, engine shutters, then regulates at 1000rpm before repeating.

the vacuum at the map does appear to have cracks on the side connected to manifold. would i connect the map, gauge, manifold with a tee to test?

 

i should add that my friend had set the idle to about 1200rpm which seemed to slightly reduce the erratic idle; i returned it to 850rpm as mentioned in the haynes manual (if i recall correctly).

 

Replace Vacuum hose to MAP if it cracked

Are you sure the firing order is correct?
It needs to be checked 3 times, and then have a friend check it...............WHILE YOU WAIT IN THE HOUSE, lol

 

i quadruple-checked the firing order and it’s correct. however, i failed to mention that, when replacing the spark plug wires, the wire set i purchased did not include a wire for the ignition coil (assuming this is different from the rest bc there’s a clip that attaches the boot to the ignition coil). i cleaned the old wire as best i could and reinstalled. not sure if this would affect spark.

also, what do the numbers mean on the wire boots (kw217, kw542, kw635, etc)? the numbers on the boots of the new wires don’t match the numbers on the boots of the old wires

 

The numbers are most likely manufacturers marks so not a reference number that would matter to application

Just rereading this thread
You know what the SPOUT Connector is?
It is removed to time the spark, then re-installed once Base Spark time is set, failure to reinstall it will cause sluggish RPM response, it is near distributor on the TFI modules wiring harness

Has the TFI module on the side of distributor been replaced, common failure point?