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97 SE, slight hesitation when warm. (Intermittent issue)


FriedEGs
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Here is the progression of my latest issues:

 

First, I had a distributor conk out on me, replaced it with an OEM Nissan reman unit and the truck has been running great ever since. However, a month later I started experiencing some starting issues with both cold starts and slightly warm engine. (After sitting for 1-2 hours max) To get it to fire up, I had to crank it multiple times in 15-20 second intervals.

 

Lately, the starting issue has since gone away but now I have experienced an intermittent hesitation, mostly after the engine warms up. Basically feels like a misfire and typically happens under hard loads, such as accelerating up-hill on the freeway. The other day I was able to 'create' the misfire by jolting the steering wheel hard in order to 'shake' the truck while at medium speeds. (around 30mph)

 

Additionally, the truck will sometimes just 'die' when slowing down to a stop or many times while at idle, both in gear or in 'park'. But, it will restart immediately with a turn of the key.

 

This intermittent problem only occurs briefly and usually only happens about 5-10% of the time, while engine is running and/or driving.

 

Again, distributor seems to be working properly. New plugs, new wires, newer fuel pump, all hoses to intake manifold appear to be fine. Also I tested the MAP and all the BARO switches below the intake, right above the AC compressor with positive results. (I checked voltage and continuity)

 

 

After reading through JeffsR50 six page 'won't start when warm' thread, I'm starting to consider that this might be related to the cut off valve which is located under the truck near the rear axle. (In-line between the EVAP canister and the fuel tank.) However, before I purchase one of those for $60 I thought I'd gather some input based on the unique symptoms I've described.

 

Thanks in advance!

 

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"Lately, the starting issue has since gone away but now I have experienced an intermittent hesitation, mostly after the engine warms up. Basically feels like a misfire and typically happens under hard loads, such as accelerating up-hill on the freeway. The other day I was able to 'create' the misfire by jolting the steering wheel hard in order to 'shake' the truck while at medium speeds. (around 30mph)"

 

This is what I've experienced a number of times over the years when the plug wires need to be changed. You have new plug wires, but if one of the boots isn't tight, it can create a situation where it's just a bit hard to jump the gap and will miss when the load is high, such as your uphill freeway situation.

 

But I'm perplexed by your ability to induce it by swerving your truck!

 

I would check in to the ignition coil and the rotor under the distributor cap. I know your distributor is newly remanufactured, but do not know the status of your ignition coil itself.

I once had my ignition coil crack and my truck would try to stall when I came to a stop light. I would have to put it in neutral before stopping and keep my foot on the gas pedal. It was fine above 1300 rpms, but would stall below that...the problem was simply the cracked coil.

 

 

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I would check in to the ignition coil and the rotor under the distributor cap. I know your distributor is newly remanufactured, but do not know the status of your ignition coil itself.

I once had my ignition coil crack and my truck would try to stall when I came to a stop light. I would have to put it in neutral before stopping and keep my foot on the gas pedal. It was fine above 1300 rpms, but would stall below that...the problem was simply the cracked coil.

 

 

 

 

This was exactly the problem I had for the last 6 months until that distributor finally crapped out. I kept chasing the issue down to the IACV, cleaning it up.

 

 

Update: Just repaired another oil leak by replacing a blown out oil sending unit. This thing was gushing oil through the plastic connector. Truck runs much better now, but had one misfire while driving it tonight.

Edited by FriedEGs
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  • 3 weeks later...

Update: Intermittent misfire still present. Happens after the truck warms up to temperature, especially on warmer days above 50 degrees. Also, stalls at idle frequently.

 

Codes: P0100 MAF Sensor > Tested the MAF circuit which gets 12 volts and the signal is measuring within spec and rises in a linear fashion, while I rev the motor. Also monitoring the MAF signal on my cell phone through the Torque app and the signal is consistent and rises with the increase in throttle.

 

Codes: P0325 Knock sensor. Basically ignoring for now.

 

Codes: P0105 MAP sensor: I tested the voltage at the MAP sensor and reads within spec. However, I have not checked vacuum, yet.

 

Fuel pressure has been constant, so doesn't seem to be a fuel issue.

 

 

Any idea's on what's going on?

 

 

Edited by FriedEGs
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It wasn't until I did a cheap cigar smoke test on my intake that I found the leak at the rubber hose at the bottom of the EGR control valve. Ive also seen that a leak in the evap system can give fits (especially after warm up) as well.

Just a little additional unexpected air into the intake mix can cause misfire for sure.

 

..Some MAF cleaner might not hurt..

 

I also had a recent stalling/ misfire issue that was solved by a cleaning of the negative battery cable connector..

 

good luck- seems like you are on the right track

 

 

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Like Jeff said, I would consider a vacuum leak in the emissions control.

 

If it was just a full-time vacuum leak, your code-start idle would be really high, or else plain crappy.

The EGR only begins to operate when warm. If you read the operating description for EGR, it will list all the conditions in which EGR is opened...if those conditions correspond to the conditions in which you have intermittently experiencing trouble, then it would be a pretty good indicator of where the problem is.

 

 

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Thanks guys! I performed a voltage test on the MAP sensor and sure enough, wasn't responding properly. I also noticed that there was no pressure reading through the Torque App / OBDII diagnostic tool.

 

Found a replacement MAP for $4 at a local Pick N Pull and so far, truck has not thrown any codes and has been performing well. Cross my fingers, hopefully the problem is solved!

 

Thanks again for everyone's support.

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