Hunter79764

I'm finishing up a 5.3 swap into an old Monte Carlo, and have been driving it in a half finished state for about 500 miles or so. I have the MAF installed directly in front of the TB (Not ideal, but the only place I can right now), but no VSS or O2's in yet (fitment issues, should be sorted out soon). I know that can cause all sorts of things to go wrong, but it seemed to default to the base tables and was running alright. I'm on a tight budget for time and money, so I had to start driving it pieced together like that.
A few days ago, it started hesitating when I gradually rolled into the throttle at highway speeds. It felt almost like a gear shift, not just a sputter or a miss. Holding the throttle at the same position results in more of the same, and if I get on it more or less it usually clears up.

The only things that changed were the weather (dropped down to 35 degrees and rainy from 50-60 and dry) and a tank of gas (from a place I go to on a regular basis).

I know that the other sensors need to go in, and they will soon, but it got me worrying that something bigger may be wrong. The engine was supposed to be a 2001 5.3, but it had a 99-2000 vortec cover on it (1st clue I should have looked deeper), and when I had the computer tuned (that was SUPPOSED to be from the same engine) it was it was a 2000 4.8l.

So if it is in fact a 4.8, but my mail-order tune is for a 5.3, would that cause problems in the cold that might not be there in warmer weather?

I'm out of town for Christmas, so I can't actually look at the car, but the more I think about it, the more I wonder if that could be part of the problem...

wait4me

iTrader: (10)

Running with a mass air meter in the wrong spot and the ability of fuel correction non exsistant with your lack of front o2 sensors, is asking for a disaster!


If your strapped for Cash, just send me over the computer, and i will at least make it safe so you dont blow the thing up...

CashDudeHomie

iTrader: (5)

I ran my 6.0 on a 5.3 tune for a few days and it was no big deal. And that's where the MAF is on F-bodies. But W4M is right, you need some front O2s on there so the computer can adjust the fuel trims before KABOOM.

Hunter79764

I have the sensors but didn't have the bungs to install them. Finally got those (couldn't find any place local that even had non-foulers in the larger size, so I had to order on ebay) and will get them installed this week since I'm off work for the holidays, but I appreciate the offer. It has stayed on the rich side by the smell test and I don't have cats on the exhaust, so no harm there, and I've been taking it easy until it started this hesitation. I'll get the O2's in place soon, I just need to figure out if there could be another issue besides that. It's a stock motor and a stock tune, but if I grenaded the engine, at least I have a full long block I picked up for cheap that I can drop in.

What would be the best location for the MAF? I've heard that you want a long straight section of pipe to get laminar flow, but it seems like the flow coming from a cone filter directly in front would be pretty even, especially with the screen in place. I could rig up some piping or something and make the old "PVC Cold Air" kit if necessary.

wait4me

iTrader: (10)

Just not right near the throttle blade and near a massive bend should be fine. If possible i like to have it in a 6-8 inch smooth non transistion tube. It too close to the throttle blade, it will mess with the reading pretty bad as the blade moves the air in different locations as it opens.

SSZ

dont be surprised if the plugs are beginning to foul. Have a look at those for that hesistation. you say it clears up when you get on it. if so then i bet one or more plugs are beginning to not fire. Hence why you gotta get those O2s in there. Hope it works out for you. i am sure it will.

salemetro

iTrader: (5)

^^^^^That, right there, is the sign of one F'n COOL person!! How often does that happen (someone going beyond just "give me your $$$, and I'll fix it for ya".)?!?!?

My hat is off to ya, Wait4me!

Sorry....just saw this thread, and his post....had to comment. That made my day.

Hunter79764

I'm always amazed at the generosity of folks like that...
Still haven't driven the car, but I think I finally got a solution on my O2 sensors, just need to finish wiring them up. After that, I'll swap the spark plugs just to take that out of the equation, since they could use it anyway. I didn't consider the plugs since it was more than just one or two cylinders misfiring, more like a round or two of misfires, but like I said, it needs to be done anyway.

Oh, forgot to mention, it does the same thing with or without MAF plugged in. Only unplugged it once, and also disconnected the battery to try to clear any bad info stored in the computer, no luck on either front. I'll get the sensors in and swap plugs and see what it looks like from there. I can usually tell pretty quick by going up a small hill just down the street, so Ill let you know how it goes.

Thanks again.

Hunter79764

Got O2 sensors installed finally, and swapped spark plugs too. Problem went away completely on the test drive for 3 or 4 miles around town, all throttle conditions.
Next morning, I'm driving it to church and after 3-4 miles of slow driving, I ease into it and it starts hesitating again, getting worse as I go. When I left, I dropped it in first and revved it up a bit under partial load, it sputtered a couple times, then cleared up. The rest of the drive had no problems, so I think I narrowed it down to dirty plugs before (and no O2 to correct anything) and improperly gapped plugs now (left them at factory gap, about 0.060+ but I've seen that they need to be more like 0.040).

I'll gap the plugs and I'm thinking that should do it. I'll also do a hunt-down of vacuum and exhaust leaks (there are a few areas I suspect of having small leaks, nothing that shows up very easily, but may add up to something significant).

Thanks for the help everybody. If plugs and leak check don't fix it, I'll dig into the tuning a little more, but I think it's hardware related at this point.

Hunter79764

Finally...
got some instruments to test it all out (vacation gauge, fuel pressure gauge, wideband O2, etc) and some time to mess with the car. Fuel pressure was good at idle, regulator seemed to work, and vacuum was decent. In the process of moving the gauges around, I bumped a wire loom and killed the engine. Traced it back to an ecm ground on the head that had worked loose. Tightened it a few rounds and problem went away. Wiggling the ground with key on made the fuel pump relay click on and off, which explains the lack of fuel issue that it looked like at one point.
Don't want to jinx it, but I think I found my problem...

salemetro

iTrader: (5)

I'm thinking that you could be right

Nexus9

A 5.3 tune in a 4.8 liter engine likely to be running very rich, but you know that. right? It's not likely that the short term or long term fuel trims will adjust that far or accurately.

Hunter79764

That's what I had figured. Turns out it is in fact a 5.3 engine, and a 5.3 tune so I'm not too worried about that aspect of it anymore. But it is good to know that if I needed to swap in my spare longblock (which is a 4.8) it wouldn't do much damage, just run a little fat if the computer couldn't adjust enough.