Team,

I've had a high RPM misfire for some time now that only happens at 5K + RPMs). After replacing fuel (pump, filter, injectors), ignition (new Petris Opti, plugs, ICM, coil), and sensors (MAF, MAP, TPS, IAT, ECT, KS), I still have the high RPM misfire. At this point, everything points to two possible sources: 1- a bad ground strap, or 2- a bad spark plug wire(s). From the lack of symptoms associated with a bad ground strap, I am led to believe it is indeed one of the Taylor Spiro Pro wires (10K miles old). I'm willing to bet it's one of the wires on the driver's side, where they rest on the brackets and other metal parts behind the PS pump.

At this point, I have a decision to make: Get new wires and do the best I can to ensure they don't arc OR convert to the LTCC system.

I am tempted to go with LTCC, but two things are holding me back: I have to solder a wire into the Opti harness, and the lack of ready-made brackets for the coils.

I am very mechanically inclined, but I can't solder to save my life.

I'm looking for smart commentary on whether I should convert to LTCC or continue messing with the awful routing of the factory setup. The end goal here is a reliable street driver.

Thank you all!

Ric

 

Ric, I am running the same red 8mm Taylor wires, except that I got the universal set in which I had to cut them to length. I also purchased the boots and terminals for the Optispark distributor side (Taylor p/n; 46052)
and crimped them on. I remember that Installing the wires into those boots were hard on the fingers even using a generous amount of dielectric grease.
I also purchased some red anodized aluminum wire separators from Amazon to keep them fairly neat and route them away from the headers. I wanted to route the wires differently from factory so that the wires and boots would not burn through. I did wrap high heat tubing around the wires (that bundle of four wires) running by the power steering pump. I have had these wires for at least 10 years with no issues. Hopefully I don't jinx myself

 

So, you suggest just redoing the wires and leaving the system as is?

 

GS,

Did you go with the 73051 universal set? All the plug boots on this set are 90*, but the 6 and 8 OEM wires have straight boots. Did the 90* work out ok for 6 and 8?

Also, do you have a link for the high heat tubing?

 

One of the first on my "to do" when chasing down intermittant or running condition problems is tape a fuel pressure gauge to the outside of the windshield and capture data on a scan tool that gives live data output.The live data can be really usefull in figuring it out.

 

The original issue I had was a severe nose dive in power after 4K RPMs. It was the OEM pump not keeping up with the demands of higher RPMs and loads. A new and higher capacity pump fixed that. I have confirmed this with the gauge taped to the WS and giving it hell on more than one occasion.

The new issue is a mild to severe misfire AND bucking AND slow gain in the RPMs. It feels like a fuel cut off, but it isn't. Temperature may have a play as it seems to make it worse. However, it is not a sensor/Opti, etc. I have swapped those back and forth with original units and the problem is there.

I have not seen any arcing from the top, even spraying water on the cables. On the other hand, I haven't got the guts to get under a hot car and spray water on the wires by the PS pump.

I have gotten a P0300 code before and what seemed like a "Reduced Power Mode". I don't always get a code and the latter only lasted a few seconds.

The car actually pulls very nicely to the 5-5.5K RPM range.

 

No, I purchased the Taylor p/n; 73251 set. I actually forgot why I chose this set. I am not sure if the wires were longer or what but it did the job.

 

Not a bad idea to tape the fuel pressure gauge to the windshield to check if the fuel pressure is the problem. I know you replaced the fuel pump, but I went through a defective new Delphi fuel pump that had me chasing my tail. The FP gauge told me that I did indeed have a defective Delphi. Then I went with the Deatchwerks DW200.

 

My bad! They are the same thing except...73051 is black and 73251 is red.

Word on the tubing?

 

See my previous post....done and everything checks out.

I got the same.

 

I'd be curious to see the MAF GPS reading when it stumbles.

 

Switching between the OEM and aftermarket MAF made no difference. Same for ICM.
I did look at MAF readings with a scan tool and the numbers were on target.

 

So I don't have the part number for the sleeve I used. Because I actually grabbed some scraps from work that were being thrown out. The brand name is Techflex Insultherm braided fiberglass sleeving. I used the 1.5" diameter sleeve, I don't remember what length I cut it at but I stuffed the four 8mm spark plug wires in it and ran it through the opening near the PS bracket. I can tell you Techflex is pricey stuff. If I remember 25 feet was around $100.00. But it is abrasion resistant and good to 1000 degrees F.
I believe Techflex also has a header/cable sleeve that is more reasonably priced.
But you can also use Thermotech or DEI sleeves, these are cheaper and would work just as well.

 

GS,

Thanks. That gives me something to go on.

 

Ohm check the injectors ... 16 is the target reading. How many miles on the car? Might be time for some new valve springs.

 

I have new injectors, Bosch 3 style from injector connection.

Valve springs is something I have considered. Based on the descriptions I have read for valve float, I don't believe that's the case. I do feel new springs may not be a bad idea.

86K miles

 

I know you said you put in a new opti, but he opti is always suspect with a misfire. If you have an old style engine analyzer available that would be one way to rule it out.

 

The original Opti and the Petris one had no effect on the misfire. It's there after 5K regardless.

 

Ric, did FIC say anything about retuning the computer because of the 26lb injectors. I know they said that they never measured 28lbs on a stock LT4 injector but I personally don't buy into that. I am sure if GM could have used the stock LT1 injectors for the LT4 they would have for cost reasons. Maybe someone else on the forum with these FIC injectors could chime in if they have had any issues using them on their LT4?

 

grandspt,
No, according to FIC, the injectors are tailored to the stock PCM tune.

I have regrets about dumping the originals.