This morning it was the same story. Cold start idle was non existant. I held it at 1500 for a few minutes and slowly brought it down to idle and it was ok then. Drove to work and it ran really pretty good but still the same WOT breakup, aligned it, started it on a warm engine and again the same crap idle for a minute or two. Ran good otherwise and every time I start it hot or cold the idle is crap. I unplugged the IAC and the idle did stabilize and when I plugged it back in it went to crap. I'm not sure whether its the IAC itself or the pcm thats controlling it and telling it to do that. A flaky IAC still doesn't explain the WOT breakup though.

 

Hmm - Well, you've eliminated a lot of possibilities through sweat equity. ECM grounds are good and clean no doubt? I don't suppose you've hung an analog voltmeter on the 5v supply (aren't all those sensors running off the 5V supply?) coming from the ECM while pecking the ECM case with your screwdriver handle?

I could maybe see the 5V regulator -> PCB solder connections getting flaky from thermal cycling over a period of tens of years, but if 5V's rock solid then no problems there...?

Didn't you say you swapped the TPS and now the idle is flaky?

You probably already know, but just in case:

In my opinion an analog voltmeter (or oscilloscope) is a good tool for locating noisy voltages like you'd see coming from a worn out TPS, A digital voltmeter just doesn't show dead spots very well. Just keep in mind, an analog voltmeter typically has a lower impedance than a digital voltmeter and can load a high impedance circuit (such as O2 sensor), I wouldn't try using a self powered analog meter to measure O2 sensor voltage.

Good luck!

 

TKR Performance - Good job, We have a winner! I remember once a long time ago I just stabbed a dizzy without setting TDC and blew half the exhaust system off my car!

Glad it's humming!

 

I had issue similar if not identical from a push fit ZIF socket. It would lose connection when I hit a decent sized bump. Ended up removing ZIF and all was well. Not sure if was chip to ZIF or ZIF to ECU? If I soldered ZIF I would have known.

 

Tried a spare PCM today and still nothing. Same results. Its either blowing the spark out or there is something going on inside the Mallory box that shouldn't be. I think I might remove the 6 easiest plugs to get to and tighten the gap to .040 from .060 and see what that does for me. If it helps I'll do the other two and see whats what. Still not sure whether the IAC is causing the cold start issue or not. It seems to have a flat spot around 30 counts but again not completely sure yet.


Its been brought to my attention that the ignition coil needs to be grounded to the engine and mine is not. I have it mounted on a piece of diamond plate along with the ignition box and both are mounted to the firewall but there is little to no continuity there. The plot may have just thickened.

 

If you can t see anything wrong in the log then more likely it not fuel related.I sounds like its spark related.You got a good point on the ground.If not have you tried a different coil?

 

I took a look at the wiring diagram for a 95 C1500 with a 350 K motor and the coil doesn't actually have a case ground. The only ground is from the ignition module which is what causes the coils primary field to do its thing. Looking at a diagram for a 5.3 liter engine the coils don't actually have a case ground either but a dedicated wire from each individual coil that in a round about way is grounded to the engine. Apparently it doesn't have to be grounded.

Looking back on this whole ordeal it seems as though the single plane intake only aggravated things that much more. I did some googling on plug gap vs performance and as engine power increases plug gap should decrease. I think what may be going on is that the single plane is making the same amount of power at 4000 rpms as the dual plane was starting to make around 5500 rpms and thats why with the dual plane the breaking up wasn't really an issue until around 5500 which I contributed to a worn out ignition system. Adding the ignition box and coil at that point did lesson the issue. After putting the single plane on it it came back only a lot worse and I just didn't put two and two together. I'm going to pull the plugs tomorrow and regap them and see what happens. They are NGK platinum plugs gapped at .060 but I'm going to try .045". Its my understanding that platinum plugs take a little more power to make a spark anyway over a conventional copper style plug so maybe I've been taking something simple and making it complicated for way too long.

 

I need to look at mine to see if the case is grounded.I got it mounted the the fire wall.As far as the 2 wire connector hooked up to it 1 wire is 12 volt and the other is the ground signal coming from the icm and pick up coil.Old me and you have the same intake and I dont have this problem.But my Ignition is stock pretty much.Im running delco r44s gapped at .040.Good luck

 

Personally I like the standard Delco copper plugs, they just work. Autolights do too but I put them in Fords.

I used to know a guy who couldn't resist the urge to swap chevy motors into fords and vice-versa, but I never saw the value.

I kinda doubt .060 vs 0.40 will make much difference with a hot coil but it's definitely worth a shot since it's free and nuthin' else has eliminated the problem.

 

I think you're onto something.

 

I went ahead and threw set of TR44s rapid fires or whatever number the delco non iridium vortec style plugs are in it just a while ago. Started it and the flaky cold start was still there which I'm pretty certain is the IAC and it did run noticably freer but all of the sudden it died like someone shut the key off. No spark. I think my Mallory box may have died. I'm going to bypass it tomorrow and see if it will run and if it does see what jegs wants to do about because it's only 7 months old.

 

im interested to see what is causing your problems. maybe it will give me some ideas

 

That makes two of us. I've been meaning to make a jumper harness so I can bypass the ignition box incase of a failure. I guess now is as good a time as any.

 

I bypassed my ignition box and the truck fired right up. Seemed to alleviate the majority of the cold start issue but it was a little shaky at first but I did crank on it for quite a while before realizing it had no spark so I think the plugs were a little damp. So my Mallory box has kicked the bucket after only 7 months and maybe a few thousand miles. Yay. First thing I noticed is the continual spark jumping sound that I've had ever since I installed the ignition box and coil. Even with the ignition box bypassed the continual spark jumping noise is still there and it was never there using a MSD blaster stock replacement coil. Its not the cap and rotor either, it did it before with a worn out cap and rotor and after with a new cap rotor and wires. Apparently the spark from the Mallory coil is just that much hotter that I can hear it????

Drove it and it ran out pretty well normal driving. Went WOT and right on cue about 3800 it started breaking up. The frequency of the misfire seems to be faster then it was before. Before it was more of a blap blap blap blap sounding misfire and now its a sort of machine gun fire quick sounding misfire. One again, if I back off to about 80% throttle it quickly pulls on up to speed and shifts. Its not lean either, running at 11.7:1 when it was doing it. Honestly not sure where to go from here. I've pretty much eliminated plugs, its done it with platinums and now AC Delco rapid fires, wires and cap and rotor seem to be fine as does the coil. The ignition box other then failing didn't seem to have any effect on it. I don't believe its anything mechanically wrong with the engine because when I lift off the throttle it will go ahead and pull for a bit before shifting.

With the MAF code there is a constant for injector phase angle (advance) and I was told the rule of thumb is to set it to what your cams intake valve opening angle is so that in theory the fuel is there on tap the instant the intake valve opens. The LT4 hot cams intake valve opening is 32 degrees BTDC IIRC which is what I used initially. I've been toying with it now have it at 20 degrees and I can't really tell that its improved or made it worse. I'm going to try 45 degrees and reevaluate and see what happens tomorrow. Other then that, I'm at a loss as to what the problem is.

 

Injectors going static?

 

I don't think so. I'm only seeing a pulse width of around 5 milliseconds at 5600 and 91 kpa. I am running 61# injectors at 50 psi. That ought to be able to out do a fire hose when at WOT. I've got a lot of room to work with in the MAF flow rate table too.

 

I don t know how much power your re losing but I had a problem problem similar to yours,turns out 1 of my injectors was shutting down intermittenly causing me to run on 4 cylinders.I found a terminal at the ecm for injector signal was slightly worn.Pulled it out of ecm,closed terminal and problem solved.I your case you can swap the injector connectors and log another run when it acts up.It will show up on your wide band real quick if the injector on the opposite side of your wide band is acting up do to a circuit problem.

 

Interesting idea.

Just had a thought this morning. With a single plane intake switching injector connectors really shouldn't change anything because the injectors spray into a common plenum. Its still worth trying but I doubt its going to make a difference.

 

Here's a long shot idea you've probably thought of but tossed out; slap a carb on there and see if it goes away... hard to do but definitely would tell you which way to go.

Another thought might be to hang an ammeter in series with the injector to see if current disappears on one but not the other?

I don't like the sound of spark arcing though, does your ECM tach signal come from the dizzy? Is it somehow possible the rotor is too far away from the respective tower maybe? It's unlikely if the tach signal comes from the dizzy but possible to have a WOT(full advance) miss if the dizzy is misaligned and the tach signal comes from a crank sensor.

I'm just brainstorming here but what if advance were jumping way out in left field somewhere and firing the wrong plug tower? You might try locking advance out just for grins and giggles?

Wonder what killed the Mallory box?

I'm running out of ideas now, should probably just shut up....

 

Did you try this?

My apologies for not rereading all the posts, BUT I recall the same symptoms on my car when I had TOO much fuel pressure. The excessively rich PE would kill the spark and can would react much as you sstated.

 

Well the plot thickened a little more. Drove it again today making only a slight AE MAP tweak and changing the injector advance to 50 degrees. Seems like a lot but it actually did help things quite a bit. It broke up a little crossing 4000 but then pulled to 5500 without issues and broke up again after 5500. It definitely helped. The likely hood of stabbing the injectors a couple of teeth off is kind of far out there considering they aren't cam driven or in any way timed to the engine so its looking like the possibility of too much fuel pressure is delaying the injector opening enough and making it that much worse at high rpms. I'm going to drop it back to 35 psi and reevaluate.

 

yeah my truck would hardly even rev past 4000 with super high pressure no matter what i did to my tune

 

Why so much pressure anyway? I always like to cut my fuel back too lean then add from there. TBI runs ~15psi normally doesn't it?

 

Synch or asynch?

 

stock OD programming normally puts you in async over around 2000rpm and 60 kpa i believe. im 99% shure hes async unless hes tuned it out

 

i was playing with my async injector offset tonight and increased it about 50% and didnt notice any difference, so i increased it another 50% and got a lean pop, so i put it back to stock. but what if i lowered it. the injector offset is kind of like injector timing is it not? never really understood how this worked.
if someone wants to explain for me?

on the other hand
i do know that my truck is alot more stable with the IAC closed to 50% during WOT than it is at 100%. it seems like the iac caused fuel distribution problems sort of like a big vaccum leak.

 

Dual plane intake? I know the early TB's have the IAC connected to one bore of the TB. The later have different passages and the IAC is connected to both bores.

 

yeah its a dual plane intake with a 454 TBI, im not shure wich model tbi it is tho. i know there were two different ones. this makes sense tho, it would make it lean on one side and rich on the other

 

Early version has the oblong plug, later has round plug.

 

mine is oblong

 

and how can i keep the IAC from shooting open when i crack throttle? dont mean to threadjack

 

I've made a little headway, uh, giggity. I lowere the fuel pressure to 35 psi and roughed out the tune enough for 35 psi to drive it. It pulls much much better now. It still does breakup a little around 5500 but it still is strong enough to keep on pulling to the 6000 rpm 1-2 shift. I would say it's 75% better. I am going to try 30 psi tomorrow and see what happens. I am going to play with the injector advance to cure what may remain. Not really sure why I was trying to run it at 50 psi other then I was trying to get a finer spray out of it but I guess you can have too much of a good thing.

 

It is at 30 psi and is currently running better then ever but it is still having some issues from 5200+ It still breaks up some but again its not so bad that it won't continue to pull. I'm going to try another 5 degrees of injector advance and see if its better or worse but really I don't think its fuel at this point. AFR was dead on at 12.5:1 when it was doing it. I was reading through the trouble shooting section of my Mallory 6AL manual and it mentions spark ionization inside the cap can cause misfire issues. It didn't say at what point but it only seems logical when that little rotor is going about 3000 rpms its nothing short of a big ball of lightning inside the distributor cap. I don't know if I dreamed this or read it somewhere but I swear somewhere I saw something mentioning spark ionization and it said to drill 3 holes at the rear of the cap at the same level the contact on the rotor sits in relation to the distributor cap. Somehow its supposed to help let the excess smoke out. Opinions?

 

Sure ionization can be a problem but if it were severe I'd expect to find corrosion along with it over a period of time. Not any examples I can recall ever had misfire without excessive corrosion due to ionization.

I say forget about trying to make a fine(er) nozzle mist, if the injector cannot control the flow due to high pressure(short on time), you're pushing it into saturation in terms of it's mechanical ability to turn on and off.

If you haven't already, why not keep turning pressure down until you run out of fuel or begin detonating(knock count begins climbing)? That's the way I always tune a carb.... squirt, squeeze, bang, fart, there's no magic, they're all essentially the same.....

 

Maybe the term I'm thinking of is spark scatter but if the air inside the cap became ionized wouldn't that end up with same result, spark scatter?

I just can't quite sell myself on ignition because the issue clearly has improved and moved too. I could probably go a little lower on the fuel pressure but I didn't see any real improvement at 30 psi vs 35 psi. I don't want to starve it for fuel although I do still have some room to work with in the MAF table. I am going to keep playing with the injector advance a little at a time and see what happens.

 

The high RPMs should not be an issue if the ignition is working properly. I have the vortec style billet distributer along with a stock amplifier module and coil. It happily spins out to 6000+ RPM and makes good power all along the way. The older HEI systems did have issues with the modules overheating and other problems that made them unreliable at high RPMs. How is your current igition laid out? How does the box interface with the rest of the ignition? Does the PCM have any say in it? Or does the box run by itself as a seperate system? Does it just use the IC reference for timing advance?

If the stock vortec stuff can do 6k+, then the mallory should also be able to do that as well with no trouble.

The injector drivers in the PCM could also be an issue. If they start to get weak, the injectors can malfunction and fail to operate properly. This used to be an issue with some of the TBI ECMs, on rare occasion. That could also be the issue, but would be hard to verify without a scope to view the waveform from the injector drivers.

 

Also, how has the issue changed as youve played with the fuel pressure/fuel flow? The MAF system should need no adjustments to teh parameters other than entering the correct flowrate and properly setting up the MAF table. The code in the MAF TBI is the same as the core fueling code in the later vortec/LS1 PCMs, which is what Im currently using in my car. The only thing you should change when you change the fuel pressure is the injector flowrate constant.

The fact that it improves with the fuel pressure lends plausability to there being an issue with the injector drivers, or the injectors themselves. Either the injectors are at their mechanical limits, or the drivers are weak, and failing. What kind of injectors do you have? Standard GM units? Smaller delphi ones?

 

The Mallory box was basically wired in so it took the place of the stock coil. The PCM still controls the timing and the box gets what used to be the stock coils power supply and tach signal/ground. Coming out of the box it was hooked up to the Mallory coil. As of right now the box is bypassed and its just the coil being used.


I thought it could be injector drivers too so I tried and still am using a spare PCM. It was removed from a perfectly good running 95 suburban. The problem initially started using the 46# injectors that came with my 454 throttle body. I thought maybe they were just too small and going static even with a substantial amount of pressure so I put my 61s back in.

For the most part all I did was change the injector flow rate and it was almost dead on. There were a few small sections of the MAF table that were not dead on and thats what I made changes to. I just recently decided to set the VAFPR table to same flow rate across the entire table and leave my vacuum regulator functional and tune it just off of the MAF table and it seems to be giving me MUCH more stable air fuel ratios this way.

Since you were the one that implemented the injector advance feature into the MAF code do you know how much is too much injector advance? Chris told me the rule of thumb is to start with your cams intake valve opening and go from there, which is 32 degrees. I've tried as little as 20 and it would hardly run, especially around idle, and as high as 50 which I'm currently at, and it other then past 5000 is running better then it ever has.

Thinking about it I think I will voltage drop the injector circuits this weekend and maybe even load test them with a head light bulb and drag test the terminals too. Could be something as simple as that 15 year old harness having some resistance somewhere.

 

The injector table and code does require that the flowrate and filter coeff. closely match the response of the VAFPR. If its off, obviously the fueling will drift.

As for the phasing. I wouldnt go over 60 degrees or so. Mainly because if its too long, you can end up having the injector pulse being commanded when the drivers are being updated by the next DRP and injector firing event. Im not quite sure how the TOCs will respond when the trigger time is overwritten before the driver has triggered. The main purpose of the phasing is to provide some way of keeping the injection pulses out of phase with the cam overlap. If you have a relatively mild cam, its probably not that big of an issue.

Back to the breakup. I can only speculate what might be causing it, but how is the fuel system set up? What kind of fuel pump do you have? Hows the regulator set up?

One reason I stopped using TBI was the issues with metering large ammounts of fuel with the stock regulators. I found that they could go into oscillation and cause the fuel pressure to pulsate (they literally would start buzzing), which would lead to odd engine operation to say the least. Another problem was pressure drop. At high flowrates, the pressure drop in some pods like the holley unit would exceed 15 PSI, which would cause the fuel pressure at idle to be considerably higher than at WOT.

If your using an external aftermarket VAFPR and just have the TBI dead-headed, then you sidestep alot of these issues.

 

Also, have you datalogged the duty cycle/PW of the injectors in the area of the breakup? At 5000 RPM, there is only around 6 msecs total time for the inector to fire. Just some quick off the cuff calculations shows that the engine could easily be getting into the static range with, say, 80 PPH of flowrate per injector above 5000 RPM. Remember that with TBI each injector has to fire twice per rev, where most SFI systems have the fuel injector firing once every two revs. Big difference in operating rate.

 

I always thought the preferred method was to not deadhead the pod and use the regulator on the return side coming out of the pod.....

 

At higher fuel pressures, its likely OK to dead-head it. Newer GMs are set up that way, with the fuel rail dead-headed and the pump bypassing fuel in the tank itself. Passing fuel through the pod means that you still have to deal with the issue of pressure drop thru the pod passages. This will cause the pressure at the injectors and at teh regulator to be different. The only provision you might consider putting in is a way to temporarily purge fuel from the TBI using the unused return port on the pod. Otherwise, its hard to purge air entirely from the pod when its dead-headed.

You can check to see if pressure drop is an issue by putting a gauge in on the supply side, and revving the engine. If the fuel pressure drops with the motor under load, then your forcing the pod to carry more fuel than it can handle.

 

I currently have the injector phasing at 60 degrees and I've got to say the difference over the initial 32 degrees I started out with is pretty amazing. I swear it feels like 40-50 hp was being left on the table with the phasing at 32 and the drivability is night and day better. It actually responds to throttle input and the response is almost knife edge sharp. It seems to like a little less AE to boot which makes sense if you think about it.

I've got an external regulator on the return line coming out of the throttle body. In the pod the I am still using the stock diaphram with the "****" removed for lack of a better term. The little hodis that was meant to seal off once the pump shuts off and that is made to the diaphram. I have a stack of washers in the spring cup (no spring) to support the diaphram from blowing down into the spring cup. I didn't want the stock springs pressure having any influence in the regulating of the fuel. The external regulator is a Mallory bypass style regulator IIRC. The return line from the throttle body goes into the regulator inlet, and then the outlet of course is connected to the reminents of the stock return line going to the tank. The regulator seems to be giving me dead on fuel pressure under all conditions. I haven't put a gauge on the windshield yet so that I can actually see the pressure while its breaking up but I will speculate at this point and say that its good.

Chris and I were talking last night and injector "ringing" came up in coversation. He said at one point he was having a similar issue more then likely due to weak injector drivers (maybe the little contacts in the transistors get worn, lol) and caused the injectors to jump or partially activate when they shouldn't be. He put a 1 ZDF (I think was the spec) capacitor on each injector to absorb the voltage spikes and said it cured the ringing issue. Seems logical considering how fast these injectors are turning off and on. I know on say a relay coil when it is turned off there is a big voltage spike for an instance and some actually have a diod built in to prevent voltage spiking the driver that controls the relay. Maybe this is a similar issue???? Seems logical.

The duty cycle seems to hover right around the 4.78 - 5.00 area. I've yet to see it go over 5.00 other then when there is a big blast of AE taking off WOT from a dead stop. At that point I've seen it jump up to 7-8 if not more.

 

More bad news. I was turned to this site by Fast355 as a possibility of the cause of the issue.

http://www.4door.com/tech_tips/tech_tip0139.htm

Seemed so simple and far out there that it just had to be the fix and sure enough it wasn't. I actually unpinned the injector wires from the connectors and soldered the capacitor leads to the crimped area of the injector connector terminals just to be sure. Its still breaking up just as bad after about 5200 rpms. Again the pulse width is right around 4.7 to 4.8 and the AFR is 13:1 and I was commanding 13:1. The only other thing I can figure is I have this nagging vacuum issue at WOT from my lack luster air cleaner setup. I don't see why it would, but is there any chance that the engine pulling 3-4 inches of vacuum (sees as low as 89 kpa at WOT 5000+ rpms) could be causing it to break up?

Doing some more thinking here. What happens if the injector connectors ever get crossed? I don't think they are but over the years they have been off who knows how many times and I'm only human... so maybe its worth a try to swap them around?

 

It will have a subtle effect on the engine, but not to the extent of what your seeing. Its worth a shot to cross them just to be sure. But, inspection of the color of the leads will tell you which connector is which.

How much timing are you commanding during WOT. IOW, whats the max timing the engine sees, or should be seeing. This thread is pretty long, so I dont recall if you mentioned that or not yet.

 

Those PWs are actually getting pretty close to 100% DC at high RPMs. At 5500 RPM, thats a DC of about 90%. This opens the door to the possibility that it might just be an inherent limitation with the injectors at very high pressures, DCs and high firing frequencies. After all, when this system was designed, it wasnt designed with the intent to be used on an engine that buzzes out to 6k and beyond. The max operating speeds with TBI in stock trim where usually around 4800 RPM. Again, keep in mind that the injectors fire 4x more often than an injector in an SFI setup. In the SFI world, there is lots of time for the PCM to set up for, and deliver the fuel pulse at high RPMs. In the TBI world, the injectors are firing rapidly one after the other to keep the cylinders fueled.

Potentially you could slow the injector pulses down and only fire each one, say, once per rev. This will cause the fueling to be uneven, though, which in itself could cause a break-up at high speeds.

 

So what you're telling me is I really probably need bigger injectors? I'm wondering about trying 25 psi. 25 psi with 61# injectors on paper really isn't enough fuel but I may be able to work with it enough to keep it from going lean. Even as it sits at 30 psi I've still got all sorts of room to play with on the MAF table.

 

well we have basically the same motor and you just have more cam. im at 25psi and its JUST enough. im so close to the limit on them sometimes the injectors go static on a super hard downshift due to trying to deliver AE. i dont have problems with that till 5200+. im going to say you need a little more than 25 psi. as far as going to bigger injectors. you will have more issues than you have now. they are bigger, so they too take more time to open and you have to do some retuning with them once again. i only had BBC injectors on mine for about 2 weeks and went back to SBC injectors quick

 

are you running E10?

 

You are telling me bigger injectors will just make things worse and smaller injectors will be too small and be lean and where I'm at now is all she wrote? Something just doesn't add up. I know guys have made more power, turned it higher, and haven't had any of these issues.

Shell claims to be ethanol free but who really knows. All gas is crap anymore.