engine rough on acceleration??? (1 Viewer)

[Lightfighter]

couple weeks ago, and very suddenly, my 97 which I drive only on weekends, started to sputter on acceleration from a standstill. Only does it while hot. goes away by 2500-3000 rpm.

no CEL.

dealer diagnostics showed it to be missing, recommended plugs, wires, cap, etc. and a fuel filter service. the tech said the plug wires were cracking. this was to some extent proven to be a crock, The wires were probably old, def not OEM, but not cracked. (195000 miles, no service history available). So, I put OEM plugs, wires, cap, rotor, fuel filter(holy s*** bittch titties what a pita), air filter. Runs WAY better out the gate. but once hot, the stumble. sputtering is still there. Over 20mph, it pulls appropriately on acceleration.

coil? Fuel pump?

any other ideas? I'm perplexed by the temperature being in play. it runs perfect while cold. fully warmed up, not so much. not horrible, but annoying beyond words.

 

[NLXTACY]

If it were misfiring you would get a PO301 through PO306 telling you which cylinder was the culprit.

 

[Lightfighter]

And that would produce a check light, correct?

 

[ZA80]

Check wiring for fuel pump resistor could be bad in connector

 

[NLXTACY]

And that would produce a check light, correct?

Every time.

 

[ZackR]

couple weeks ago, and very suddenly, my 97 which I drive only on weekends, started to sputter on acceleration from a standstill. Only does it while hot. goes away by 2500-3000 rpm.

no CEL.

dealer diagnostics showed it to be missing, recommended plugs, wires, cap, etc. and a fuel filter service. the tech said the plug wires were cracking. this was to some extent proven to be a crock, The wires were probably old, def not OEM, but not cracked. (195000 miles, no service history available). So, I put OEM plugs, wires, cap, rotor, fuel filter(holy s*** bittch titties what a pita), air filter. Runs WAY better out the gate. but once hot, the stumble. sputtering is still there. Over 20mph, it pulls appropriately on acceleration.

coil? Fuel pump?

any other ideas? I'm perplexed by the temperature being in play. it runs perfect while cold. fully warmed up, not so much. not horrible, but annoying beyond words.

I'm in a similar situation with my 94'. There's a hesitation around 1700-2000rpm (when the engine is warmed up) that clears up once I go past 2000rpm. Cap, rotor, plugs, wires are less than a year old and no check engine light is on. Fuel filter history is unknown (on my to do list) but even higher on my list are 02 sensors that were last replaced 12 years ago/100k+ miles. MPG is a pretty consistent 12-13 in mixed driving however when pulling into traffic I find myself mashing the pedal down a bit more to get past 2000rpm to avoid the hesitation.

Good luck on getting this one solved, I'll be interested to hear what the outcome is.

 

[ajax1]

Fuel injectors

 

[Litig8r]

Did you ever figure out your misfire issue? Mine is doing the same thing. Started at the same time my brake booster went out, and I had a stuck open thermostat. Both replaced now, but still misfiring. Happens a little bit at idle, but bad on take off until about 2000-2500 rpm, then smooth as always. On the highway it purrs.

 

[Lightfighter]

replacedd the cap, rotor, wires and plugs. the stumble was still there, but the truck ran better(the tune up was probably long over due).

replaced the fuel filter(and messed about with the resistor wiring, but did not actually replace or test anything) and a couple days later, the stumble was gone. havent seen it since


coincidently, as soon as I replaced the fuel filter I drove it 200 miles to tucson in ridiculas heat at 85mph, and I am wondering if the new filter and a romp on the throttle didnt just get some bad gas out of her. I dont drive it but a few 15-50 mile trips a month normally

 

[ZackR]

No resolution yet. Thus far I've tried new spark plugs (denso), new spark plug wires (napa gold), new air filter (wix OEM style), checking the intake tube (no obvious leaks, seems newer), new vacuum lines, running water into the intake via vacuum hose to clean, and disable EGR (disconnect vacuum lines and use resistor for signal). Just recently I've been running some B12 chemtool in the fuel to see if that cleans up the injectors but I'm still having the hesitation (although not quite as bad, might just be the placebo effect). When I replaced the distributor O ring recently I set the ignition timing to 7-8deg (FSM calls for 3deg but many others go higher without issue). I didn't check the previous setting before taking out the distributor.

I suspect its a fuel injector issue (based on the symptoms and ajax1's comment) but haven't removed the manifold to have them cleaned. If this B12 chemtool helps further that would confirm the suspicion. Before I remove the intake manifold to pull the injectors I want to have a plan of attack for the PHH, fuel filter and EGR VSV (this is my prime suspect for the code 71, hence disabled EGR).

As things stand now:

No CEL
The engine starts right up (no matter the temp)
Idle is good 95% of the time, sometimes it drops to 300-400rpm.
MPG 12-14 depending on what I'm doing
O2 sensors are old (140k miles and 12 years ago they were replaced with bosch)
Hesitation from takeoff-2000rpm when warm then smooths out. Much less hesitation when cold.
Timing at 7-8deg, no pinging

I'm hopeful a professional injector cleaning, fuel filter and some new O2 sensors will really help. Any advice people have to offer is much appreciated.

 

[Litig8r]

I was recommended a tune up yesterday, but based on what people are saying, I'm not hopeful it will fix the stumble. Seems like it's getting worse, but still only up to 2000 rpm or so. Found a major tune up kit at cruiserparts with plugs, wires, cap and rotor, pcv, etc. Gonna do that next weekend and see what happens. I did the plugs 55k ago, but I think the wires and cap/rotor are OE. I'm at 205k, so probably long overdue.

I'll report back after the tune up. Thanks for all the information guys.

 

[blkprj80]

Long Shot: Check your injector connectors. They should alternate colors from front to back. If you have two the same color on adjacent cylinders, they are swapped. Engine will run okay-ish at high RPMs and stumble off idle and at low RPMs. The colors are gray and brown.

Apparently it is possible to swap them, usually toward the back.

 

[Litig8r]

I'll check that.

 

[beefcan]

You could try cleaning or replacing the air flow sensor ?

 

[wlittleman]

Any success, ZackR? My hesitation problem only happens when the engine is cold. There was improvement when I used Techron fuel injector cleaner, but 1000 miles have gone by, and the problem is starting to return. I'm guessing that my injectors need to be cleaned, and replace the fuel filter and possibly the fuel sock.

 

[ZackR]

On mine it turned out to be the wiring harness near the EGR valve. I had 3 wires with burned insulation (shorting against each other) and once those were repaired the hesitation and missing went away. It wasn't obvious from looking at the outside of the wiring harness, I had to peel off the old heat tape and cut the loom to find it. If you haven't yet its definitely worth a look and more common than I would have thought.