cmac2012

About 2 weeks ago, I started having severe missing and lurching in my van, a 1989 Chevy with a 5.0 liter. I had been needing to call my mechanic with an issue about my Mercedes SDL so while I had him on the line I picked his brain on the Chev. He asked me when was the last time I did a tuneup. It dawned on me it had probably been 20 to 30,000 miles ago.

So I put in plugs, cables, cap and rotor, and air filter. It miraculously started running much better. I’ve never had so dramatic a change from a tuneup, but then again I used to do them more regularly.

Then a week later it started displaying the same symptoms again. And me all WTF? It seems more than the missing of a single cylinder, the whole engine loses power for a second, then regains it for a moment.

I did a search for symptoms of a bad coil, and it sounds a little bit like what I have going on, these especially:

#3 – Engine Misfiring.
#4 – Vehicle Stalling.
#5 – Engine Jerking, Rough idling, Poor Power.

I’m wondering if the tuneup cleaned up enough trouble to enable the faltering coil to have a bit more life. Even when it started running much better after the tuneup, it did not seem 100%.

It has 173k, I’ve owned it for about 50,000 of those, might be the original coil.

Again there was a dramatic improvement. And then several days ago it came back again, the hesitation, the loss of power. My mechanic buddy took off the EGR line, said it was likely stuck open. I replaced it and the solenoid, no improvement. That felt looking thing in the EGR was falling out, so I suspect it was indeed bad.

I’ve been having quite a bit of smoke on start up lately. Power is pretty good but not quite like it used to be. I’m wondering if the original issue was too much blow by with major fouling of the plugs. Perhaps that’s why it ran so much better after the tuneup, Just the new plugs.

I’m going take it into him on Monday, he’s very good, I’m not half bad, but he is way beyond me. I’ll suggest a compression check and see what he thinks. I am resigned to a new motor if necessary. The body’s in fairly good shape all in all, people are always wanting to buy it. The same mechanic rebuilt the tranny a year ago, did an excellent job. One of my major questions in this thread is should I stay with a 5.0 or move up to a 5.7? If I had Jay Leno’s money and garage I might think about putting in the diesel of my dreams, but I don’t think that’s going to happen.

Triaged

My go to on issues like this is to look at it in the dark. If purple glowing ants seem to be walking out of the coil replace it. I had a coil go bad on a TBI. It was worse under load and when the engine was well warmed up at first then got worse and worse.

As for injectors if it's TBI you can use a timing light to look at the spray pattern.

cmac2012

I already replaced the coil, just based on the mileage it seemed like a reasonable investment and easy enough to do, not too expensive. But I’ll try the technique you speak of in future, sounds interesting.

I’m getting ahead of myself a bit, I don’t have as good of a set up as I once had for working on my own rigs, and I really like my mechanic, he’s good, he’s been around for a while, he knows the old rigs.

A compression check would be a good first step I imagine, I would think a fuel pressure test as well.

Also, I rebuilt the TBI several years back. There were a few steps I was uncertain I was getting correct or not.

William Kisselstein

Any codes in it?

Got a you pull yard nearby? Find a TBI truck and pull all the sensors, MAP, EGR, everything but maybe the CTS on the intake - they're only $20 and will make it run rich when they fail, they're easy to change.

make sure it's not getting damp in the distributor.

cmac2012

The only code is 43, which is: “knock sensor error.”

Coincidentally I just looked at the best bone yard around here for trucks, Pick and Pull has one on the waterfront, it’s in the Southbay, Fremont, it’s undesirable land. Too flat and a bit smelly.

I was hoping to get an entire fuel line from the TBI down to where hooks up at the front. There are several trucks from theTBI era, but virtually all of them have been picked over pretty badly. I couldn’t see the throttlebody. Except on one. And it had a lot of stuff removed. You really need to watch Pick-n-Pull’s Website closely. When a vehicle first arrives you have to jump on it. If you get there a week late, a lot of stuff will be gone.

RoadTrip

Sounds like it could also a fuel pressure regulator. A fuel pressure test could confirm. Rebuild kits are available at Summit for about $40.

cmac2012

That does sound promising. It’s painful to admit but I’m only half of a mechanic. There’s a lot about engines that I simply don’t get. Four years ago I took it to the same mechanic for an issue that had been bothering me for more than a year. I didn’t drive it much back then, so I could deal with it more or less. It would stall at stop signs, traffic lights. Just did not have good function at idle. Reversing was like pulling teeth, I had to keep one foot on the gas, one on the brake, serious jerking motion.

I had done everything I could think of, throttle position sensor, new cap and rotor, other small things. He discovered it was the distributor itself that was bad. He showed me the old one, the thing barely turned. I’m lucky I took it to him before it died completely. I had never thought to look at the distributor itself.

I’ve not done a fuel pressure test, I don’t have the equipment for it. I’ll ask him about it.

This is a frustrating problem. If it had been a bad fuel pressure regulator all along, I can’t figure why the basic tuneup would’ve made it run really well for more than a week before the symptoms came back.

I discovered the knock sensor was not hooked up, I popped the line on but I was still getting the code, I have a new one, will put it in soon.

cmac2012

OK, raise your hand if you thought the hesitation problem was a CAT that was disintegrating internally. I needed to get it smogged now anyway and I just barely passed HC two years ago so I figured a new CAT was in the works. After he told me about the disintegrating CAT I consulted the Google and sure enough, there are opinions that say such a CAT will lead to hesitation and surging, which is exactly what I had.

He said the new CAT improved performance but still not perfect. He had to put in a T connection with nipple on a fuel line in order to test the pressure. He said it was only at about 6 or 7 and it needs to be 13. New fuel pump installed. Runs ideally now.

While the tank was out he looked it over for crud, said it looked pretty good.

just before I took it in I got two new codes: 33 and 44.

33: MAP sensor circuit error (signal high indicating low vacuum)

44: Oxygen sensor error (lean condition indicated)

Not sure if any of the work done will address either issue, my guess is no. I haven’t gotten the codes since the repair was done.