Engine acting uppity and occasionally omitting oomph

[boatboy]

My truck is acting up and I can?t figure out what the problem is. Sporadically, she loses power when driving. She will idle just fine when this happens, but no power to push me forward. When this happened a few times last week, I could get power back by pushing hard on the accelerator and I could speed up, but then she would revert back to her no-power-mode and I would slow down. This would not start until she had been running for about 20 minutes. Today it just got worse- she started losing power just after I started my trip. Engine would cut out at about 1700 rpm pretty consistently. And this time, she wouldn?t respond to a heavy right foot to speed up- this just seemed to put the engine in spasm and she jerked around making me look like I?d never driven standard before. I could drive fine as long as I didn?t rev the engine above 1700- which made for some slow starts off a red light. Then I stopped for 20 minutes and she drove fine?!?!?

I replaced the fuel pump with OEM two years ago. And fuel filter. Also replaced the Vehicle Speed sensor at the same time. It is a ?95 so she doesn?t have a crank position sensor to fail. Ran a bottle of injector cleaner through a tank of fuel to clean the injectors, but no difference.

It seems like a sensor? But which one? Or maybe failing ECU?

Yes, throwing an engine code- 45= right lambda sensor- but I would guess this is from the right exhaust manifold leak. I must get to that. But I wouldn?t think this would rob me of all my power. Am I wrong?

My searches came up empty. Does anyone have any ideas?

Thanks!

 

[FatMcNasty]

when mine does that its time for a new cap and rotor.. I'm also on a 95. Iv seen a lot of Beck/arnley (sp) rotors that were bad and allowing the spark to travel through it and to the center post of the Distributor. Thus bypassing the plugs all together.

 

[boatboy]

cap and rotor are a very good start- thanks! I missed them completely in my diagnostic thought process. They are more than a couple of years old, so it is probably high time to replace them anyway.

 

[KyleT]

iirc the speed sensor failing gives off symptoms like this.

 

[boatboy]

I had thought of this because I have had it fail before. but I just replaced it two years ago, so I was hoping that wasn't the problem. However, if it failed once, it can fail again.

I forgot one other symptom- when the power cuts out, if I keep the accelerator pedal down, but put in the clutch, the engine cycles between 1000 rpm and 1800 rpm, although the pedal is steady. the revs just bounce back and forth until I let it drop down to idle, then it returns to normal. Strange behavior? It is stranger than my ex-wife!

 

[boatboy]

So, I have been driving a bit more and have narrowed down my symptoms a bit. The engine power will consistently cut out at 1700 rpm, but if I allow the rpms to fall below 1250rpm, the engine will regain its power. This is very consistent. As I mentioned earlier, when the engine loses power, if I put in the clutch but maintain my foot on the accelerator, the rpms will cycle between these two numbers (not 1800 and 1000 as I had said earlier). What would be controlling the engine and have cut in/out at these rpms?

I am wondering if this is an ignition issue. If I turn off the engine while coasting along and then turn it back on, the loss of power symptom will go away for a few minutes, but is back again after a few gear shifts. I tried this a few times yesterday to power up a hill while towing a load and it worked… until the one time the truck refused to start again. I let it sit for five minutes at the side of the road and she started right up again.

The idle is getting worse too- sometimes good at 700, often a bit low at 500. Yesterday trying to get the thing home, she wouldn’t idle at all and I had to keep my foot on the accelerator at lights to keep her running.

So: power loss at specific rpm, power regained at specific rpm. Erratic to no idle. Occasional non-start. I don't think this is distributor cap- the symptoms are too specific. And I checked my records and I replaced this just a year and a half ago. And have only put about 1000km on it. I don't think this is speed sensor, since the symptoms are very engine speed related, not vehicle speed related and my understanding is that the sensor is measuring the final drive speed, not the engine speed. And when the VSS died a year and a half ago, the symptoms were very erratic.

does anyone have any ideas of where to look? Could this be my ECU? What controls the initial higher idle speed when the engine is started?

 

[carlosz]

have you checked the alternator out put and state of battery?, load test it... these things are very sensitive to low current/spikes it may be your batt is in a weak state thus the alt doe not put out enough to keep it chrged and power is demanded the ignition system draws but there is no delivery thus attempting to shut down but ecu input dictated other wise.

 

[braves6117]

When I screwed up my MAF sensor, my truck gave me symptoms like this....power cut out at 2300RPM, kept foot on gas pedal only to have power come back at 1200RPM (RPMS would dive to 1200RPM even with foot on pedal).

 

[boatboy]

thanks guys- I did load test the battery a few weeks ago and it seemed fine. It is only a year old. and turns the engine over smartly. I will check the alternator output though. MAF sounds like a very likely place to look. Cody, your symptoms sound very similar- almost identical.

 

[Agent]

First thing I'd do is swap the MAF. My '99 was doing a very similar thing. Would idle fine and initially drive a little, but when I tried to accelerate it would choke and start missing. Couldn't get about maybe 1800rpm. New MAF resolved the issue. These trucks do some very wierd things when the MAF starts to go.

 

[carlosz]

tps maybe?

 

[d1driver]

Do a search for VSS and see if symptoms are similar.

 

[boatboy]

tps and vss are both possibilities and crossed my mind as potential culprits. my vss went a couple of years ago and that would cause the truck to die, but it was much more random than this. this is very precise in when the truck cuts out. I think I have a spare MAFS in my parts box from my donor truck, so I will try swapping that in and if that doesn't work, I will re-address the issue. Always hoping, of course, that the spare MAFS, being used, works to begin with.

 

[crown14]

Being that is truck is a '95 model and given the symptoms I don't think the VSS is as likely as it would be on a 96-99 D1. Does the GEMS even have a speed related fuel cut?

If I turn off the engine while coasting along and then turn it back on, the loss of power symptom will go away for a few minutes, but is back again after a few gear shifts. I tried this a few times yesterday to power up a hill while towing a load and it worked… until the one time the truck refused to start again. I let it sit for five minutes at the side of the road and she started right up again.

I would get a fuel pressure gauge on it and go for a drive, watching to see if it fluctuates. Fuel filter should be replaced yearly if you drive this vehicle a lot. The injector cleaner you used might have helped remove gum or varnish but won't matter if there is rust particles in the fuel rail clogging the injectors.

 

[carlosz]

I dont think the ignition module would be a culprit because this one is remote mounted so it sshould stay cool unlike the older models where it was mounted on the side of the distributor and it tended to overheat and short internally but anything is possible specially under load failure.