Hey everyone,

Here goes the story.. About a week ago, we shot down to the store, and on the way back, I noticed that when I hit around 2500RPM, the engine would sort of surge in a wave sort of pattern.. yeah, real weird.

I kept recording the ALDL and looking for a goofed up sensor, etc. I went in the computer (I am able to program it,thats another story), and I tried to disable EGR to see if that was causing the weird surge.. Nope, so I turned it back on.

I checked the fuel pressure.. It was 55PSI, and it only drifted to 20psi after several hours, so I don't suspect a fuel leak.

I did some reading and decided to throw in a new ignition module, and the problem still existed, but it uncovered a new problem!

I was test driving with the new ignition module when I noticed that when I hit the brake, the headlamps would seem to flicker a bit. I was thinking 'ah hah! Alternator'. I then turned on all the accessories, and when I turned on the heat, the whole truck went BLACK.. no lights, no running, no nothing.. DEAD. I was driving down a road with no city lights and I almost lost it because I couldn't see a thing!

Well, I pulled it over and one by one the accessories and such came back and I was able to start it again so I went home.

Today, I took out the alternator thinking it was definately the problem, and took it to autozone.. They tested it and said "its good".. I had them test it 8 times, every time good.

Ok, so what could it be? A ground? I checked the resistance between the block and the frame - 0.1 ohms.. I checked the alternator-battery wire.. 0 ohms. Battery to frame, 0.1 ohms.. I'm at a loss.. Is it possible that the alternator is in fact bad and it just tested good?

Does anyone know the locations of the grounds? I found one on the frame by the battery, one right next to the battery, one in the 'fron't of the motor directly connected to the battery, and one on the firewall near the heater fan resistor.

I also noticed last night that the lights seemed to flicker in the car, like the alternator was bad. Since it tested good, I put a new battery in it tonight when I put the alternator back , but the headlamp flicker when you press the brake thing is still there.

Any help would be greatly appreciated!

Jim

 

It it almost certainly a bad ground somewhere. There are dozens of possible locations for your bad ground and any number of them could be the culprit.

I had a similar flickering dash light issue in my S10 that after several days of tracing wires ended up being a bad ground that had rusted off way back at the trailer hitch wiring.

However considering what happens when you turn on all of your accessories at once you probably have a bad main ground rather then a small grounding wire like I had.
Or perhaps one or more of your battery cables themselves are bad or have corroded connections that need to be cleaned or replaced. The same could be said for a bad wire from your alternator to the main harness.

 

Thanks for the advice. I just replaced the alternator for the hell of it, and the light issues are better.

I spent the day measuring grounds and everywhere it was 0.2 ohms or less. I also cleaned any grounds that I could find.

Now I'm on to the original problem. Sometimes, When I take off and hit around 2500 RPM, the engine will start to 'jump'. That is, the engine will go up and down in RPM and the truck lurches.. It will either stop doing it, or if I slow down it will stop.

I can't think of any sensor that would cause this to happen, unless the computer is doing it? I can't figure it out at all. Mechanically, the engine is good and no coolant issues (not drinking it, putting oil in it), no oil issues (oil looks clean and not losing any).

I checked the fuel pressure as mentioned before, but I will have to do it again while its running to see if it happens then.

I was possibly thinking 'bad valve', but I don't believe it would be intermittent like it is. Sometimes the problem doesn't happen?!

So, I'm thinking possibly TCC, Cam/Crank sensor, or some sort of mechanical problem. If anyone has any input please let me know!

Jim

 

*UPDATE* haha

Well, I was monkeying around with it tonight and when it hit 2500 RPM, I just kept pushing it.. And, the motor died.. I can't restart it. I had to tow strap it home at 1:30am too.

The fuel pump was running, it turned over but no ignition. I suspect either spark or fuel. Mechanically, perhaps timing chain or something, but I'll start with the spark/fuel diagnosis first. I did check the fuses and they were ok.

Jim

 

UPDATE #2: Of course this morning, it started right up. Argh now I can't reliably diagnose it as easily.

I looked at grounds, connectors, everything and I cannot find a problem at all.

Finally, right before I gave up for the night, I took the IMTV valve off the plenum, and looked down inside. I saw a few clean spots near the #6 cylinder injector area inside of the intake. Its funny because the fuel pressure doesn't really drop that much, but perhaps its in the injector line and not the fuel pressure regulator.

Would this cause it to not start once or should I keep looking for another problem? Can the injector get in a state where it freezes and will no longer spray?

 

Well, I think its fixed!

I finally figued it was the fuel injector, and I was right. I installed a new CPI 'spider' and all the problems I had went away! No more:

* Bogging at light throttle
* Hesitation

I ran my scanner and noticed that when I accelerate now, the O2 sensor swings. Didn't use to do that!

 

Um, thats great. however I am not sure how a spider ahs anything to do with total power loss.

typically when teh whoel truck shuts off like that your battery cable to teh starter is loose or full of corrosion and needs to be replaced. Give that cable a few good yanks and see what happens. While your yanking on it see if you can see any green stuff where the sheathing ends. If so that is corrosion, it gets under the sheathing and eats cable. Ohm test is worthless for battery cables. All you need is one path for the electricity to follow to get a good reading on a cable that size. Try testing it with a lot more juice. The ends look fine, but the cable between the ends is toast. Also verify your cable if firmly attached at both ends. Been in your shoes and my fix was a new cable, not a spider assemble.

 

Well, I ended up having several problems. I think the total power loss was a result of a bad battery connection or alternator. I put a new battery and alternator in it.

One time it refused to start (just cranked) a few days after I did the battery/alternator thing. That was either fuel or spark, and since I had a new ignition module, I was assuming fuel.

I opened up the plenum and noticed the passenger side was totally clean - a leaking regulator (which I later confirmed when I removed the regulator, it was leaking out of the hole).

After replacing the 'spider' assembly, all the stupid hesitation I was fighting from the beginning was gone. It is running great now, better than I ever had it running. It was definately a learning experience though I'll tell ya that!

My major mistake was that the previous owner told me he replaced the spider, and I thus assumed (incorrectly) that the injector would be good because it was new. Turns out that it was the cause of the problem after all.

Before replacing it, I had to 'fool' the IAT sensor by adding a 1.5K resistor in series, to fool the truck to think it was about 20 degrees colder. For some odd reason, if I didn't do this, the truck would surge and sputter on acceleration, but only after entering closed loop. The whole thing was puzzling.

I 'unfooled' the IAT sensor and returned it to the factory state. Still running good and no surging at take offs anymore. So, I'm safe to conclude that those problems are behind me.

Now the only thing that I notice is that when I for instance hit the brake pedal, the interior dome light will flicker and dim a bit (if its on, that is). Seems like this would be unusual if the truck was running to me. I checked all the grounds and cleaned them, but now I'm thinking about your theory. I'll take a look at the cables and see if I notice any corrosion in them, but overall they look pretty good.

Jim

 

ok since we r all on the wierd elec issues. my voltage meter ticks back and forth when the blinkers are on. the amp and subs or any other elec system doesnt cause this to happen. years ago uhaul shorted out trailer harness which shorted out the lights ( fuse replacement fixed the lights) trailer harness hasnt worked properly since. any chance maybe its the ground from the harness gone bad causing this? if so where does this ground wire run to from the bumper?