stumped

[offroader83]

Have a 99 with 3.0L. When cold start doesnt want to stay running. When finally stay running surge badly and cant give it any gas, it studders and dies. When it warms up a little it will idle a little better but still drops on idle and comes back up. Changed fuel filter with no help. Checked injectors and all 6 are clicking. Unplgged the iac and idle drops down real low and barely stays running. Have sprayed all over top half of engine with brake clean with no changes. Have replaced maf, tps, cps and syncro. All new gaskets from the head gaskets up. Truck has just got me stump. Yesterday I unplugged the flex fuel sensor and it ran great but today still like crap even if unplug it again. O and to top it off no cel. Had them before with codes reading running lean bank 1&2 upstream and bank 2 downstream. Then codes cps and syncro out of sync or faulty pcm. Have no computer to hook up to other then basic code reader. Thank you to all that can help.

 

[Spott]

I would check your fuel pump. Also, maybe your injectors are dirty or worn. Don't just replace stuff; you should check things first.

 

[offroader83]

Its range is 55-75. Its get 55 lbs pressure last checked. First start up will idle rough and die, but runs a little it starts idling smoother.

 

[offroader83]

Previous owner had all new injectors put in last December. Can get rpm up 1500 before it starts to drop out and studdering. Only in park. Put it n gear and soon as you touch the gas starts studdering. If you playwith the throttle can get it rev it up higher but do it that well when in gear.

 

[RonD]

Previous owner had all new injectors put in last December. Can get rpm up 1500 before it starts to drop out and studdering. Only in park. Put it n gear and soon as you touch the gas starts studdering. If you playwith the throttle can get it rev it up higher but do it that well when in gear.

Injectors just don't fail that often, my '94 4.0l has original injectors, and in all my years of wrenching I have never replaced a set of injectors because of engine issues, 1 injector yes, but never a set.
What I would read into that is that this vehicle has had issues before.

Unplug the MAF sensor and start engine, you should get a CEL(check engine light), that would be good.
If no CEL shut off engine and unhook the TPS(throttle position sensor), start engine, you should get a CEL.
If not I would guess your computer is the issue, and probably has been for a long time, unplugging the flex fuel sensor lead to this, that should have given you a CEL.

Low idle with IAC unplugged means no vacuum leaks.

Hard starting and limited REV ability could be blocked exhaust system, check tail pipe with engine idling and also, if possible, with engine REVing as much as possible, you should feel nice hot exhaust with good flow that changes instantly with RPM.

 

[modelageek]

Its range is 55-75. Its get 55 lbs pressure last checked. First start up will idle rough and die, but runs a little it starts idling smoother.

Was the 55 both KOEO and KOER?

ECT?
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[offroader83]

The 55psi was KOER. Will check with unpluggib maf and other sensors when ran lets up. Dont have the truck sitting in a garage and starting to ran here where I am at, but will get to them as quick as I can. Exhaust has good flow when idling. Will have to try to get my wife to help check flow with throttle. When I have unplugged the flex fuel sensor it took it a little while for CEL to finally come on but did end up comingon for it. Will post response as soon as can. Thank you

 

[offroader83]

Unplugged MAF sensor took a little it but kickex code. Unplugged IAC and ended kicking code. Pulled intake tupe off and gave throttle body a shot of starter fluid while trying to rev up and it revex up great. Not sure how to do volume testing for gas and dont have a pressure guage for checking it

 

[modelageek]

How are you getting a 55psi without a pressure gauge? I would like to see what the ECT is doing?

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[offroader83]

The 55 psi was from when had first checked by a shop and told me it had a vaccum leak. Not sure what you by the ECT tho.

 

[modelageek]

The 55 psi was from when had first checked by a shop and told me it had a vaccum leak. Not sure what you by the ECT tho.

So the shop told you the pressure with the truck running was 55?

ECT= ENGINE COOLANT TEMP sensor.

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[offroader83]

Temperature gauge moves good. Yeah they told me 55 psi but didnt see it myself. With the other checks that have done. Starting to think it is a fuel issue but not sure exactly where.

 

[modelageek]

Temperature gauge moves good. Yeah they told me 55 psi but didnt see it myself. With the other checks that have done. Starting to think it is a fuel issue but not sure exactly where.

The ECT is the sensor for the ECU. It has nothing to do with the temp gauge.

Find out if the 55 was KOER?

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[modelageek]

Torque + elm327= $10
fuel pressure gauge= $20
multimeter = $5


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[RonD]

ECT = Engine Coolant Temp sensor, this is a 2 wire "Sensor" only used by the computer.
The is also a 1 wire "Sender" that looks similar, this one is used for the dash board Temp Gauge.

The ECT sensor reports coolant temp(so engine temp) to computer, when cold the computer runs engine in "Choke mode", high idle, advanced spark timing and rich fuel mixture.
As ECT/engine warms up computer reduces the idle RPMs and leans out the fuel mix until it reaches operating temp(about 5 min.), 190degF, then computer uses O2 sensors to adjust fuel mix.
ECT sensors, like other sensors, rarely fail, not never, but a quick test with ohm meter will usually show it is fine.

Computer bases ALL fuel mixes on the MAF data, this sensor tells the computer how much air is coming in to the engine, so rich or lean is based on quantity/volume of air it is being mixed with.