Low speed stumble.....

[katmol]

I just bought a 1994 Sidekick for my daughter. It's in great shape but has a lot of miles on it. It runs great if you keep the RPM's above 2500-2600. But when starting off in the band of 2000 to 2600 RPM's it shudders and then and then smoothes out. It's a five speed and you notice it most when in first and second. I put new plugs and plug wires on it but it didn't help.

[ranger88den]

Doesn't cost any money to check for a vacuum leak. Check hoses for disconnection of cracks. Good luck, Dave

[jtgh]

8valve or 16valve ? LOOK ON TOP OF VALVE COVER. OR TBELT COVER

if top of engine says 16ALVE it is, If nothing marked ,then 8v.
nothing is more important to diagnosis , this nfo.

if 8v , and you have a vacuum leak , it races all the time, HIGH IDLE.Hot.
if 16v, and you have a vacuum leak , it will run lean and buck and bog, hesitate,and be gutless (backfire thru TB too)


try pinching all the hoses ( starting with the tinyones)
do not pinch the bigger hose to the IDLE control valve.
Do not pinch the PCV hose (big)
Do pinch the big hose to the Brake vacuum booster !
if the rpm drops during above tests, you have a leak.
if we knew what engine you have , we could be more accurate.
do not pinch breather hoses.

most important.?
how does car run Cold (perfect?)
how does car run Hot ( as you said, it bogs)?
how does car idle, HOT ( cold is 1200) but hot must be 800 rpm.?

great idea that tune up.

VAC TUBES TO TEST: guessing at 16v. [ by symptoms]
eVAP SOLENOID VALVE
EGR SOLENOID VALVE.
ALL SMALL HOSES ON THE FROt OF THE intake manifold 16v
loose EGR valve (air leak) or bad gasket under it.
loose ISC , valve same.

[katmol]

It is a 16 valve. Also the front cylinder has low compression 75-80lb. It does not smoke at all. It did idle high till I changed out the thermostat. It was stuck open. No telling how long it had been run like that.

[jtgh]

170,170,170,75,
if that's the ratio the engine my only make 45-50 HP
pulling a week cycl has a profound effect.

id check for any vacuum leaks like range88 said.
free and will cause your MAF to Lie like a dog.
the ECu says X air flow but reality is X Plus 10 or what ever.
Lean city. If the attains closed loop , the MAF is making the rules for air.

I bet the engine runs like a rocket cold , RIGHT ? ?????


then when the engine warms up and attempts closed loop it becomes
super lean (rich profile ends).

dont forget to check the pipe from the MAF to the TB for any air incursion !!!! too.

[Shconer]

This sounds alot like a worn timing belt pully key. Maybe check the timing.

[katmol]

OK, then here is my question. My mechanic is telling me that the compression problem is most likely valve related. Does this sound right?

Originally Posted by jtgh

170,170,170,75,
if that's the ratio the engine my only make 45-50 HP
pulling a week cycl has a profound effect.

id check for any vacuum leaks like range88 said.
free and will cause your MAF to Lie like a dog.
the ECu says X air flow but reality is X Plus 10 or what ever.
Lean city. If the attains closed loop , the MAF is making the rules for air.

I bet the engine runs like a rocket cold , RIGHT ? ?????


then when the engine warms up and attempts closed loop it becomes
super lean (rich profile ends).

dont forget to check the pipe from the MAF to the TB for any air incursion !!!! too.

[jtgh]

he probably , squirted engine oil into #1 and repeated the compression.
and the value didnt increase, which indicates burned valve.

when you tuned it up, did you check timing at the distributor.
at the mark, and not jumping like mad , indicating loose Tbelt.
Requires diagnostic plug jumper to tell ECU to Freeze timing so you can check it. if timing is way off , suspect jumped belt or bad crank key on damper pully.

the weak cylinder is impending doom, it will never get better, and it will get worse at an advanced rate. (burning begets burning further).

If it were mine, rebuilt head and new Tbelt and idler pully.
now comes the while your at it crowd.......

[katmol]

So rebuilding the head should take care of it, maybe? Do you think I will need rings???

He's quoting me $800 +/- just to rebuild the head. Is that high?

Thanks.

Originally Posted by jtgh

he probably , squirted engine oil into #1 and repeated the compression.
and the value didnt increase, which indicates burned valve.

when you tuned it up, did you check timing at the distributor.
at the mark, and not jumping like mad , indicating loose Tbelt.
Requires diagnostic plug jumper to tell ECU to Freeze timing so you can check it. if timing is way off , suspect jumped belt or bad crank key on damper pully.

the weak cylinder is impending doom, it will never get better, and it will get worse at an advanced rate. (burning begets burning further).

If it were mine, rebuilt head and new Tbelt and idler pully.
now comes the while your at it crowd.......

[jtgh]

it think $300 is par for rebuild head swap
labor? per hour varies by local.
In SA its $10 hr. Have son there now, in USA its $150 hr (up to)
how many hours, well 4 or so? (order head first pay core)

The better question is, who gives the best warrantee and at what cost.
you next door neighbor will do it the cheapest with 0 warrantee.

its more then parts and labor. IMHO.