Hi Guys, 91' p/u, 4cyl ,5spd,113K.
My uncles truck, according to him problem is ~6 month old

As your going thru the power band, power is ok until~1/2 throttle and ~3000rpms(guessing, no tach) Then it just takes off like a scared rabbit an pulls hard all the way up. Best analogy is it acts like a fouled plug clearing.
I assume a smooth transition all the way through is Normal right?
Engine starts and idles fine also revs fine.

Had original ignition components, So I sprayed H2O on wires in the dark and had a great light show. New plugs(autolites), Napa wires,cap ,rotor. Also put some Gumout injection cleaner in,(Only 20 miles since). Checked for Vac leaks. Check Mass air flow meter and it isn't hanging up.

Is there a TPS in this system? MAP sensor problem?

Any ideas appreciated. Thanks

 

There is a TPS located on the opposite side of the throttle control lever. To check it you will need an ohmmeter and feeler guages. The TPS controls the timing so this may be a good place to look.

This may be a longshot, but if the TPS is ok, see if the EGR is sticking.

 

Runner, Do you know the procedure for checking TPS? I'm going at this blind(no manual) Also best way to check EGR?

Thank you!

 

TPS check:
http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

EGR can be removed, cleaned and manually checked.

 

The best way to check the EGR valve is to block off the EGR pipe at the back of the upper intake plenum. Loosen up the two bolts, cut up a small section from a Coke/Pepsi/Beer can and jam this piece between the plenum and pipe. If the problem goes away, you either have a bad EGR valve or it needs cleaning. Don't forget to remove the makeshift block off plate once you're done testing. You can also pull/plug the vacuum line going to the EGR valve but this test isn't as accurate as the test above.

 

That 4crawler write-up should do the trick. If you have problems, email me: damendman@yahoo.com

 

Thanks Guys! I'll do the EGR test tonight and post back.

 

-I did the TPS test with Ohm meter, and it's in spec.
-Blocked of EGR port at back of plenum and no change
-Cleaned Throttle body(didn't remove) wiped, sprayed down vac ports
cleaned back of blade.

Not much improvement. What I did notice, it runs alot better(close to perfect) when the engine temp guage is at 12:00.
Ie. I took it for a test ride and when it got to full temp it was pretty good.
I took it back to shop and did some more TB cleaning for ~15 mins.
Engine temp had dropped a little as did performance. When Temp guage
was at 12:00 it ran good.

Question, Could there be a temp sending unit problem and it'd not dumping enough extra fuel? It has a high idle, and performance is consistent from cold
to right before full temp.

Any other ideas appreciated.

Thanks!

 

I know that the temp is considered in the computer while it maintains the engine. However, I don't know how that works. I bet someone here: http://www.4x4wire.com/forums/postli...t=&Board=UBB11 will know.

 

You have a cold start injector time switch and coolant sensor mounted at the front of the lower intake runners. To test 'em you'll need a multimeter and FSM to verify whether they're good/bad.

 

There's actually a cold start injector? or just a timer to dump more fuel out of injectors? It will run high idle~45-60 sec then starts dropping down to normal idles speed.

Does the coolant sensor feed both puter' and analog guage on daash?

Thanks guys!

 

I'm pretty sure there is a coolant temperature sensor, and if I remember right, it is near the back side of the intake. Try a search for Memphis4x4, as I believe he was having a problem with his coolant temp sensor. See if that yields anything and post back...

 

Your cold start injector is located on the side of the upper intake. It has a metal line hooked up to it that originates at the fuel rail. The cold start injector switch/sensor opens/closes the injector depending on coolant temp. Your idle speed is controlled by a built in air flow valve in your throttlebody. This valve allows air to bypass the throttleplate thereby increasing idle speed when the engine coolant is cold. As the coolant temp rises, this valve gradually closes bringing the idle speed down.

The main coolant sensor for your ECU is mounted on top of the thermostat housing. The sender for your temp gauge sits in the middle of the lower intake right next to the cylinder head.

 

Do the symptoms Jive with either sensor or CS injector?
Anyway to test them if so?

Thanks Arnold!

 

btt Thanks

 

Last Call............

 

What prob are you experiencing again? Checking 'em is pretty simple as long as you got a FSM. Unfortunately, I don't have mine at the moment since I let a friend borrow it. If the parts are bad, changing 'em out is a piece of cake.

 

Truck runs good, idles fine etc.

As you accelerate, I think the power is good, you get too~1/2 throttle and ~3000 rpm and it's like a turbo spooled up and the power is great!

The "good" power before 1/2 throttle is much better when the temp guage is pointing at 12:00 and fully warmed up. So my thought(new ignition components, checking TPS, EGR, TB clean) is either the temp sending unit is not telling the ECM to dumb enough fuel or the cold start injector isn't functioning properly.
Power is good even when engine is cold at initial startup, so I'm leaning away from the CS injector.

Any other ideas appreciated

 

Last call again..........