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Resolved 1G Constant Misfire

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doebelj1

Proven Member
30
3
Jan 13, 2014
Raleigh, North_Carolina
Hey guys, I've done some crazy researching about this and haven't been able to pin down a solid answer for my problem. It's a two parter, so bare with me.

I have a ton of misfire happening over the entire rpm range, boost or not. Even idle has some misfire. I've done some diagnostics and found that when I plug a timing light to the coils number 1 and number 3 fire consistently. Though, number 2 and number 4 seem to misfiring. I read that misfire on two coils means your coil pack is going. But I thought that 1 and 4 were connected and 2 and 3 were connected. Is it still possible that the 2 and 4 could be misfiring together? And that would make my coil pack bad? FYI I have brand new NGK 7es's gapped to .030.

I also noticed when I do a boost leak test the air seems to run straight through the head and right out of the exhaust. I can't find a leak anywhere, but the system only holds 3 psi. You can clearly hear it dumping into the header and running right out of the exhaust pipe/wastegate. Should this be happening? Would something like this cause misfire?
 
Question: aren't injector resistance supposed to be between 2 to 3 ohms for turbo setups? But, that might be for stock 450's Blue Top injectors.. 550's have a different resistance value?

Now, heard somewhere on the board here that the resistor pack that is bolted to the firewall for 1G's was a low resistance pack for the injectors and going to a different size of injector might need that resistor pack changed out to match the new injectors - please someone bring some light on that area for I'm not totally clear on that but it was an area of concern just the same.

You might have been duped by the previous owner on the fuel pump area if you say it looks clean and untouched - which could explain the issue with No 3 if your FP isn't enough to feed those four 550's.

DSM
 
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Question: aren't injector resistance supposed to be between 2 to 3 ohms for turbo setups? But, that might be for stock 450's Blue Top injectors.. 550's have a different resistance value?

Now, heard somewhere on the board here that the resistor pack that is bolted to the firewall for 1G's was a low resistance pack for the injectors and going to a different size of injector might need that resistor pack changed out to match the new injectors - please someone bring some light on that area for I'm not totally clear on that but it was an area of concern just the same.

You might have been duped by the previous owner on the fuel pump area if you say it looks clean and untouched - which could explain the issue with No 3 if your FP isn't enough to feed those four 550's.

DSM

Resistance has nothing to do with rather a setup is boosted or not.

There are two types of injectors, High impedance (saturated) and Low impedance (peak and hold).

Fuel Injector Clinic sums it up best as follows from the fact page:

What are the differences between low impedance/peak & hold and high impedance/saturated injectors?

The older fat body style low impedance injectors (1.5 to 4.0 Ohm) used to have faster open and close times due to the type of electrical signal pattern emitted by an ECU equipped with proper P&H signal transmitters. This “Peak and Hold” injector signal typically uses a high (4 amp) initial current to open the injector, and which reduces to a lower (1 amp) current to keep the injector open until the pulse ends. Since this method put less total current into the coil, the coil heated up less and was therefore more reliable. Since the “hold” or lower current part of the signal has created a weaker magnetic field, the injector will also close more quickly.

High impedance injectors (10 to 16 Ohm) are triggered by a low (typically around 1.2 amps) constant current signal and kept open by the same constant (saturated) current for the entire cycle. Most OEM injectors today are high impedance injectors being driven by saturated injector signals from the ECU since car manufacturers are most interested in the simpler saturated signal which is more cost effective to produce when building ECU’s, especially where there is no apparent loss of drivability or performance.

Why do I have a (injector) resistor pack (box) in my car?

The resistor pack is installed to ‘fool’ your ECU into thinking it is driving high impedance injectors. Vehicles that have low impedance injectors AND resistor packs have ECUs that use a saturated signal to operate low impedance injectors.

You may know, or have read earlier in our FAQ How do I know if my injector is low impedance or high impedance? that low impedance injectors are designed to be driven by peak and hold signals. Most of the OE manufacturers that produced cars with low-Z injectors chose a “workaround” to using the low-Z injectors since it wasn’t cost effective to produce an ECU with the necessary circuitry and injector drivers to produce these P&H signals for the few high performance cars that needed it.

The way they solved the problem was to add a resistor box into the fuel injector harness, thereby increasing the resistance in the circuit to the higher value needed to prevent the ECU injector drivers from overheating due to excessive current draw. (e.g. low-Z injector resistance is 3.0 Ohm, plus in-line resistor of 7.5 Ohm, making a total resistance of 10.5 Ohm, which is safe for the ECU).

The fuel pump is plenty to feed the car at idle where it is still mis-firing so the conclusion that it is too small in itself holds no merit. If the car were leaning out in the upper RPM's or mis-firing up top I could see the fuel pump size being a possible issue.

Robert
 
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Excellent report and thx for the help on the detailed content within the report.

Still odd that one coil firing two plugs at the same time and were the OP has erratic issues with the one side of the coil.

Here's something to toss out just to "condemn" a part of the equation: Just run a spark plug wire, but not connected to the No.3 plug, bare the connection end so it will spark to ground and see what happens.

If the spark emitted is still erratic, then we've "condemned" the spark plug showing that part of the equation is ok. But, if the spark from the wire flattens out to normal, we have a grounding issue with the motor area.

DSM
 
I didn't think about the ground, good insight. I've seen quite a few threads about guys having problems with engines not being grounded properly. And think I remember reading in Hayne's Manual that a pour engine ground will have you chasing non-existent problems.

By bare the connection, do you mean just pull the connector so it's out away from the boot and can touch a ground?

I just drove the car 1000 miles from MI to NC. I didn't have much choice. But there was practically no power. Though, when I got it into high rpm range (3600 and above) it ran, and boosted just as smooth as can be. There was still definitely some power loss, but it didn't sound boggy or like it was misfiring. I'm gonna get that throttle body figured out today and tomorrow, maybe it's sucking in so much air, it's killing my power? and causing my laggy condition?
 
On the topic of grounds: I've recently been having CEL light issues and searching funky sensors that the ECU codes are coming up with, yet in the meantime, my starter was getting ready to die on me.

Thus, got the old starter out and got a good reman installed with while being under the vehicle doing the install, I made sure that all of my grounds were rock tight .. and one ground cable attached to the manifold that runs to the battery was a bit loose, thus I tightened that one down super tight along with the connection to the lead battery connector(in which i took apart, restripped the wire so I can get bright copper shining again and tightly crimped the end in the battery connector along with the other two grounds-one from the tranny and the other from the firewall), and got connections super clean and tight..

And what's odd is that I suddenly have some more power, CEL light issues disappeared and even my MPG increased a bit. I figured that, with that starter going out, it was doing something funky with the ground that passes through was some sort of issue causing the problems listed above..along as you mention that poor engine grounds can have you chasing for non-existent problems.

What do No. 3 spark plug look like: Dark and looks like it's been running cold, or blistering white from a lean mixture?

Put the car on idle and zap some WD40 around the movable areas.

If rpm's suddenly take off, that area is definitely pulling in a lot of air leaning out your system and giving you that "laggy" condition.
 
Put a ohm lead on pin 55 at the E.C.U harness and go under the hood with the other lead and see if there is a good connection to the power transistor and the # 2 and #3 coil pack, this may help diagnose the spark issue.

My guess is there could be a short in between the E.C.U, and the coil pack.

it might even be worth it to test all the E.C.U harness pins, and the E.C.U grounds under the hood.
[pins 17,24,101 ,104, 106 on a 1990 dsm E.C.U harness are all listed as grounds.]

and any corrosion or oxidation on wires, or their connectors will leave you with spark issues so make sure you inspect the wire harness for corroded, frayed, or cracked wires.
 
Well I spent the entire day replacing the seals in the throttle body. I got them through motion industries for $21 (they're the size of a dime!) Being in North Carolina though, I have a quarter of the resources I had in Michigan. I have no way to boost leak test but am sure there are still more lurking under the hood. However, my throttle response has increased ten fold, it's almost too touchy. Before I'd have to put it down to the floor and slip the clutch reeeaalll slow to get the rpms to hold enough for it to get moving; it takes right off now.

There is still quite a lack of power though, and it only gets about 8 psi of boost pressure. It still backfires insanely on deceleration, and it still misses. Though it doesn't miss as bad. My timing light down here is no where near as good as the one I had up north but it looks like 3 is still missing, and 1 misses sporadically now as well...? The weird thing about it is plug 1 looks perfect, nice an' brown through and through. Though plugs 2, 3, and 4 have white porcelain, black rings, and slightly white tips. It's clearly running lean and I have to have a boost leak somewhere.

I have a major exhaust leak at my flex pipe now, I'm not even sure if exhaust air is reaching the muffler. Between this and a big enough boost leak, could these explain my clear loss of power? I find it hard to believe it would be tied into the misses as well... but could it incorporate?

I appreciate all the responses, they have been monumentally helpful in this frustrating situation!
 
Thanks again all for the help. I had to bring it into a muffler shop due to the exhaust leak and I don't have the tools to weld it in NC. But I had them run some diagnostics on it while they were there as well. After 2 days they said I had the spark plugs gapped incorrectly and needed new ones. Little upset it cost me $60 just to hear that, but I still wasn't convinced it was my problem.

I kept poking around and bumped into the number 1 injector plug and heard the idle change. Sure enough, when I pushed down on the plug the engine would stop misfiring and run just as smooth as can be. For now, I zip tied the plug down on the injector and the car seems zippy as can be. Odd thing is, the misfire read in number 3 and the number 1 spark plug looks the best out of any of the plugs (not lean or hot). Still feels like there might be a boost leak, but the power has returned and the misfire dissipated! Not sure if the ECM sends a signal to retard the other cylinders or something, but it looks like it was my number 1 injector plug the whole time. Thanks again for the help!
 
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