Hard to crank when hot

[snrusnak]

I'm pretty new to tuning, been watching a lot of videos and doing a lot of reading, etc. I had been playing aroudn with tuning the MAF a lot but think I'm chasing my tail...

Car is a 2006 CTS-V (LS2) witha 402 stroker, TF heads, BTR4 cam, etc. A fairly high hp N/A build (by previous owner, so I don't know 100% of the details). It is also tuned MAF only, which I recently discovered playing in hptuners. Speed density is disable above like 400 rpm or something like that. I say I'm chasing my tail because I can't get the MAF dialed in. I have read that it's tough to tune a MAF at low airflow with a big lopey cam. I plan to try to enable the map this weekend and give tuning the vve tables a shot...

The current issue though... As I've been doing the MAF tuning I've noticed when I shut the car off to make adjustments then restart it hot, it is really hard to crank. It cranks super slow, almost like it's not gonna turn over. It has a brand new battery, and I'm pretty sure the starter was recently new by the previous owner. I think it has something to do with the tune.

One other note (may be related), when I first got the car I had cleaned the TB (it was very dirty). After that, the car idled crazy high like 1500rpm. I couldn't drive it obviously. I spent months trying to figure out the issue, and what ended up resolving it was just arbitrarily reducing startup airflow and base idle airflow by a large % across the tables. I think I took out like 30 or 40%. After that, the car idled and ran good. Now I'm wondering if this could be related to the hard hot starts? I attributed it to the car being tuned with a dirty TB, so when I cleaned it the base airflow was all jacked up...

Any help is appreciated. I have tried pulling some startup timing but it didn't seem to make much difference...

[Casey A]

For the mechanical side, High compression (and large stroke) engines can be hard on starters (it may help to know the compression ratio here). Also, tightly built engines (tight bearing clearances, piston to wall clearances ring clearances) will start very hard when hot due to the different expansion rates of metals. I would check all the wiring around the battery, cables, ground, and main cable to the starter. Check to make sure the alternator is outputting between 13.5 and 14.2 volts (at least 13 anyway). Check and make sure there are plenty of ground straps between the engine, frame and body of the car. Any corrosion, bad connections, weak battery or alternator, or even a failing starter can cause this. If the problem persists and nothing seems to help, maybe get a high torque mini starter.

As for the tune, I am newer to the forum and HP tuners so I don't know a lot that can help. Where I would start in the tuning process is with the starting air and eq ratios. Add some air to the start tab and see if it gets harder or easer or no change. If no change is noticed, take some air away. If still nothing revert it back to the current settings.

If you wire your wideband to a constant hot with a switch instead of a ignition hot, you can let it warm up before the start sequence. Turn on the wideband, put your key in accessory mode, connect to the vehicle with your tuner, wait for the wideband to warm up and show AFR (should be showing way lean with the engine off), start log, and do a maf eq error table with just the start procedure. This may allow you to see if the engine is starting way too rich or lean. You wouldn't need more than about 10 seconds, but you could perform the process multiple times on one log to let the average come out....

Dont use this info to adjust the MAF table, as this is for a running engine. Use the above method to help you adjust the air and fuel on start sequence only.


Casey

[snrusnak]

Thanks Casey, I understand your idea about monitoring the wideband for starting, I can try that out as my wideband is powered during ignition on. I didn't build the engine so don't know exactly, but I did the best I could to estimate CR a while back and it was basically same as stock, which I think is just under 11:1. I made one or two logical assumptions in there, like I think deck height and head gasket thickness. I think I was able to find all the other info needed.

I plan to play with starting airflow this weekend a bit like you suggest to see if it makes a difference. I recently went through a lot of the front of this car and checked a lot of grounds. I rerouted the alternaotor wire to get it away fro mthe headers, etc. The car has no rust or anything, I really do not think it's a wiring/loose terminal/etc. issue. One think I've noticed (just by monitoring the voltage displayed on the radio screen) is the voltage does seem kinda low sometimes, like in the 12's. Sometimes it's normal, though, in the 13's. I wonder if the VR could be faulty? The car also has an underdrive pulley, so the alternator is I guess turning slower (and so is the water pump....which is causing slightly higher temps at low rpm)...

[Casey A]

did you do a Throttle Body calibration after you cleaned it? The throttle bodies (if I understand correctly) are adaptive and will adjust over time to being dirty, when you clean them they have to be "reprogrammed" to adjust to the new conditions. A google search will tell you the best way to do this, just look up a vehicle that has your motor from the factory. Check your commanded throttle position, desired throttle position, and actual throttle position. These will tell you what the engine wants and what is actually going on. My 5.3 gen 4 runs in about the 5% range at idle. If all this is relatively close:

New Theory, starter overheat.

This is a stroked engine, and you said the starter had been replaced. Id bet someone threw away the starter heat shield; these are one of the first pieces to be removed from most engines. As you said, the motor runs a little hot, especially at idle. If there are headers this is even more of a possibility. When you shut down the vehicle, if you wait 10 or maybe 15 minutes does it start better? This is usually indicative of starter overheat. Three solutions if this is the problem, find a heat shield if yours is missing, use an insulated starter wrap, or convert to an aftermarket mini starter (these usually have more clearance between the body, block and headers....

Casey

[smokeshow]

Post the file. Depending on compression and IVC with the cam, you may have to yank more spark out at high start ECT. Monitor voltage during cranking as well.

[snrusnak]

I'll double check but believe it still has the starter heat shield. I do have longtubes, and the engine bay is super tight in these V's so it gets hot under there. The ECT doesn't run super hot, but for example if I cruise at 55mph in 5th gear it'll hold 200-205 deg F, if I shift to 6th and hold same speed it'll rise up to 210-215 deg F. At idle once hot it'll hold around 210-215 deg F. It's not an airflow issue, I have the efans coming on early, have a 180tstat, recently replaced the coolant about a year ago with an aftermarket oversized aluminum radiator, etc. It's a low rpm water pump flow issue. But I don't think I ever really have seen it above 215/220 deg F so it's nothing crazy, just would like it to hold around 200.

I eventually plan to coat the headers inside/out which will likely help the heat some. I can try a mini starter also, I'm not positive but a common mod for these cars is a "truck starter" so I'm assuming that's what's on this one. If I wait 15 minutes it still starts slow. Like it cranks slow, it's hard to turn over. Once it turns it fires right up. If you didn't know any better you'd think it had a bad battery. I recently replaced the battery, it did it with the old and new battery.

I tried the idle/TB relearns that are posted for my car, none of that worked. I think they tuned the car with the TB dirty, and when i cleaned it there was a slightly larger amount of opening for air to get in, and the base airflow was all jacked up. I tried relearn procedures, driving it a bunch (which was really difficult....imagine trying to pull out the driveway in a nearly 500rwhp car idling at 1500rpm with a clutch lol). If you let the car sit and idle it would get super hot, it must have been very lean, the leaders started to glow one time and I shut it off. I never really drove it much until the issue was resolved. I went to a local guy who does some tuning and after being stumped for months we decided to arbitrarily cut startup airflow and base idle airflow and it worked. I'll post a tune later on, the tune files are on my other laptop... Sorry, but what is IVC? I tried pulling spark already during startup, I can try pulling more. I think at the high ECT like around 220 deg F I'm at 3 or 5 degrees. I believe it was at around 9 before I made the change. I'll post the file later...

[smokeshow]

Kind of goes without saying, but make sure all your connections between starter and battery are clean. Outside of possibly low voltage to the fans due to a common dirty power connection, I doubt the start issue and overheating at idle are related.

I worked on a similar issue at an OEM once though. Excess vaporized fuel in the intake manifold after a 10-15min hot soak allowed the engine to fire up without any injection at all. Wasn't possible to control the fuel mixture either, and given that all the fuel was homogenized/vaporized, it was really good at making torque. If that's what happening in your case, it explains why removing startup airflow helped. Start airflow causes large changes to fueling before the engine is in run mode which can affect the tendency for preignition.

You might try holding the pedal to the floor while cranking to enter flood clear and see how it behaves with start fuel removed. That helped me diagnose it before. If preignition is involved at all, its making torque way before TDC and decreasing crank speed and beating the hell out of the starter.

[snrusnak]

So I think I may have confused you a bit. Several things happening here... As far as the removing a bunch of startup airflow, that was like a year or two ago due to a high idle issue after cleaning the TB. That had nothing to do with a hard to crank issue or anything. Starting it cold it would idle normal, then once the engine was up to temp and you touched the gas pedal it jumped to like 1500 rpm. That's when we arbitrarily reduced base idle airflow to "Fix" that issue. Maybe though once it's hot it is doing what you are suggesting.

I believe the somewhat/sometimes low charging voltage and the low rpm hotter ECT is due to the underdrive pulley on the balancer. Maybe a worn water pump also... If you raise the rpms slightly the issue goes away. And it's not a huge issue, but the car does run noticeably hotter at low/idle rpm.

[snrusnak]

Ok here's some tune files.

First is the as found original from when I bought the car.
Second is the tune that fixed the high idle issue, I pulled some startup airflow and base idle airflow across the tables.
Third is after doing a bunch of MAF tuning (chasing my tail). I have several things turned off like decel fuel, clutch fuel, O2 readiness, pulled 5 deg timing, etc.
Fourth is my latest tune, same as third other than I also pulled some additional startup timing at the high ECTs to see if it helped hot starts.

Tune 1 -Original As Found Tune.hpt
Tune 2 - New idle tune.hpt
Tune 3 - MAF tuning.hpt
Tune 4 - Startup changes.hpt

[snrusnak]

So this morning I did a few things...

I looked at the original tune the car had when I bought it, and the startup airflow was like 45% higher, so I copied and pasted that table into the my tune. I also copied and pasted the stock cranking timing table to my current tune. I drove around the block with the log running and got it up to temp then stopped and sat for a couple minutes. The "control module" voltage (I think that's what it was called) was right above 14v while driving, which seems good. During cranking it got as low as 8/9 volts. I'm not sure if that's normal. It immediately recovered and only dipped during the cranking process. When I started the car hot this time, it seemed to start fairly well, not much different than when cold. Note, though the engine bay wasn't "heat soaked".

My wife and I then went on a coffee date and drove about an hour away. Stopped and got gas and the hot start was not a whole lot better than it has been. It did seem slightly better, like it cranked good (faster) but right when it fires it almost makes a clanking noise or just a noise that sounds bad lol. Maybe preignition/detonation or the starter being overloaded and wanting to kick back...??? You know that noise that movies use when a car is breaking down, they'll show the car jerking and slowing down, kind of sputtering and making a clanking noise? It's sort of like a rattle/clunk noise? It sounds like that for a split second right when it fires. The remake of "gone in 60 seconds" when the eleanor mustang clanks and breaks down, it sounds just like that but for a split second right when it fires.

Drove to coffee shop a few more miles, sat and had coffee/breakfast for about an hour. When I restarted the car the ECT was at 183 so it had cooled a bit. It started pretty good, almost like it would cold. So this is making me think it's a "heat soak" issue, maybe?

The startup airflow increas of like 45% didn't seem to have a very noticeable change, what should I have noticed?

I also tried holding the gas to the floor in flood mode and it just cranked and wouldn't fire. I let it crank about 5 seconds then started it like normal and it fired up like normal.

I also guess the tap I used for my wideband is not hot during cranking as the gauge goes dead during cranking then has to go through the heat up mode so I can't currently monitor A/F ratio during cranking.

Thanks for any help! As for the cooling system issue it pretty much ran around 210 today cruising around. I dropped it to 5th gear and got the rpms up to like 2200 the last couple miles home and it pretty quickly fell to 197 deg F and stayed there. Certainly seems like a water flow issue.

[Casey A]

The wideband setup you have is the same as mine, you can let it heat up, but when you go to start mode it goes back to warmup.

As for the knocking or dieseling, in older cars is usually equated to 2 things, High compression or timing too advanced (could be wet intake as well). This is detonation, or combustion happening too early in the piston stroke. You can try to pull some timing out of the start sequence.

Also, like smokeshow said, when you held the throttle down and cranked it, then you did a normal start sequence; were you saying it started almost fine at this time? holding the throttle down will help the engine clear out any leftover fuel. After this, the normal start cycle would have been closer to a cold start. If this is the case, you will have to defer to smokes help as I am still learning this area. There are tables in the fuel tab for dealing with wet intake runners / valves vs valve and coolant temps. Adjustments can be made but I don't know which way to go and how much to help your situation.... Adding more start air may remedy this as well.

Casey

[smokeshow]

Ok, just noticed this. All files including the original have min spark clamped at 8? over the whole table. Remove that garbage, put the stock values back in and then repeat all tests over again. Also...if you post a data file of a crappy start, we could have spotted this spark issue very easily

[snrusnak]

Thanks Casey A, so there's no way I can monitor starting AFR huh?

As for how it started after I did the "flood" mode I think it started pretty much like it has been, hard to crank. But honestly I'll have to test it again cause I can't remember lol. I've pulled some cranking timing advance, how much can I pull? I mean if I get to 0 is that ok or should I keep going to retard the timing?

Smokeshow, I'll look for that table and see if I can fix that. Thanks. I can post data files also. Sorry, I"m still pretty new to this! lol

Is the cranking voltage drop to ~8/9 volts OK?

[snrusnak]

So I found the minimum spark table (don't know how I missed that previously when I compared to a stock tune file....I guess I didn't scroll down far enough). Fixed that and will drive the car probably Friday and see what effect that has. I'll be out of town the whole week after that though so won't be able to work on it again for a while.

Thanks again.

[blindsquirrel]

You don't by any chance have one of those piece of shit Optima batteries, do you?

[snrusnak]

No sir blindsquirrel. I've known a few folks who had those and they were garbage. I have a walmart everstart maxx battery. It's a group size larger so has more cranking amps. I'm writing the tune with the updated (stock) minimum spark table now, will drive the car to work tomorrow and see if there's any change.

[snrusnak]

So drove the car to work today. Started fine at lunch time after it cooled a lot (~115 F). Started pretty good after lunch after it cooled for ~30 min (190 F). After I got home I shut it off, waiting about 1 minute and it started terrible again (215 F). I did log the whole start and drive home and the restart hot at 215 F. I'll post them shortly... I noticed the cranking fuel tables (only the higher ECT temps) are modified for added fuel. Thinking maybe trying to modify them, or maybe try stock.

[blindsquirrel]

Or maybe verify the basics first. Get after it with a DVOM that can record high/low... check min. voltage while cranking, and voltage drop on both the B+ to starter and B- to block.

[snrusnak]

Sorry what's DVOM? I'll have to look in the service manual to understand the B+/- info, will look into that thanks. I'm monitoring voltage while cranking and it gets into the 8/9 volt range. Not sure if that's normal. It's control module voltage, don't know if that matters. Here's the drive home log and the hot restart log. I dunno what the hell happened with the drive home log but most of the info isn't saved, the MAF error is all jacked up, etc.

Cold start, drive home from work.hpl
Hot restart after drive home from work.hpl

[blindsquirrel]

Digital Volt Ohm Meter.

A voltage reading in the scanner is about as relevant as... well, something that isn't very relevant, from a diagnostics standpoint.

Cranking voltage is measured directly at the battery terminals, preferably with a comparison between what it is while cranking when the engine is cold and starts easy, and when it's hot and starts acting up. If there's a significant difference between hot & cold there is a problem. The scanner is reading a voltage through all the inline connectors, and is also interpreted by software. Not a direct measurement with a real instrument.

A voltage drop test tells you the difference in voltage between the start of a wire and the end of that same wire while it is under load (or, from one point in a circuit to another point, to isolate a problem down to a single connector, for instance). How much is lost along the way. One meter lead to battery negative, other meter lead to the block while cranking will tell you how much voltage is being lost in the ground circuit. If it measures 2 volts, something's wrong. That means you'd have say 11.4 under load at the battery terminals but only 9.4 available to power the starter. The higher the current flow through a resistor (or a bad connection or cable), the higher the voltage drop, or difference, between input side and output side.