Ignition Breakup in gears 4-5 @ low rpm

[marshall13]

I have a 98 GST with a 1g swap from a Galant VR4. At low RPM's (2,000-3,000), while holding even cruise throttle, all of a sudden the engine makes a rumbling sound like all the cylinders are firing at once. My A/F ratio goes as lean as the guage reads (20.0).

To get it to stop I can push the clutch in and let it idle down and then let off the clutch and it's fine for about 10 seconds when it does it again. It won't do it for a couple of starts after I reset the ECU.

I just put a new TPS on the car and tested it for proper voltage so I know that's right. It did it a lot worse before the new TPS, intake, plugs and wires. I checked the coils for fire and logged it on my mechanic's scan tool, but I don't see anything out of place. Any suggestions would be greatly appreciated.

 

[TALONTRAX]

What method are you using to defeat the 6 bolt/2G random misfire issue? That`s what it sounds like to me. What type of 1G cas are you using for the cam/crank signals?

 

[Nvisabl]

quoted from Road race
Be prepared to buy DSMLink and 95-E-Prom ECU if your Stock ECU is unhappy with
the simulated Crank signal. Its the only viable solution to eliminating false
Random Misfire detection if the problem occurs

We have done quite a few of these swaps with about a 50/50 result your ECU doesn't like the CAS signal DSM link will fix the problem.
Good luck
Merry Christmas
DJ

 

[TALONTRAX]

+1 on the Dsmlink & eprom box . . . I`m running a custom chip w/no misfire check on the chip code, & a black top cas with zero misfire issues . . .

Happy holidays everyone !

 

[Nvisabl]

+1 on the Dsmlink & eprom box . . . I`m running a custom chip w/no misfire check on the chip code, & a black top cas with zero misfire issues . . .

Happy holidays everyone !

Your just not getting the code but your ECU doesn't like the CAS one thing we have done with limited success is to run shielded wire for the signal. If you don't have shielded wire wrap signal wire in alum. foil it seems to help some. I don't believe the chip will eliminate mis-fire it just doesn't set a code.


DJ

 

[TALONTRAX]

That`s interesting . . . The way Jeff explained it to me was, That when the ecu doesn`t monitor for misfire (just like the potentiometer mod.), the actual engine misfire from the simulated cas signal is eliminated because the ecu no longer compares variation from the individual 2G crank & cam signals, that are now combined into one with these swaps. I have had not 1 single misfire since the newest chip . . . it does work - believe me !

 

[TALONTRAX]

I forgot to add that, this is true with or without cas. inversion on the chip code. I have run it both ways & have never had a single misfire issue . . .

 

[marshall13]

By the way, Merry Christmas to all of you.

 

[marshall13]

I think it has an eprom ecu. I say "I think" because in the manual I have for my MAF Translator, the guy who owned the car before me wrote in at the top of the baseline setting table about pre-eprom, stock, and eprom injector size settings. I can't tell you for sure because I was not involved in the build as it was built up before I got the car, and the shop that built it has a really hard time telling me what is in this car. Why is it that straight answers are so hard to find these days?

I do know, though, that it has a 3" GM MAF, 2G intake manifold. I know I don't have DSMLink. Expect for this engine to be redone complete with an EMS system, but in the meantime, I gotta get this thing right. I am starting a ministry in January called Christian Car Club, and this car and a 300zx are the main draw for us. I got it tuned pretty well except for this one problem that's left.

 

[marshall13]

Oh, and the Cam Angle Sensor is a factory piece. Could the CAS possibly be replaced and somewhat remedy the issue? I think it is having misfires at low RPM's because you can hear the uneven "popping" sound in the exhaust while holding even throttle. I'm not used to an engine being so cantankerous.

 

[TALONTRAX]

If your 2nd. gen(95-99) has a 1st.gen (6 bolt) engine swap in it, the cam & crank signals are generated by a 1st. gen cas. as the 1st. gen engine has no provision for the 2nd. gen crank sensor. So, your car must have some variation of a 1st. gen cas to trigger the ignition. The problem is, that the 2nd. gen ecu in your car doesn`t "like" the signal from the 1st.gen cas because it is a simulation of the 2nd. gen crank sensor signal, which is not as precise, hence the misfire problem. As stated above, you must determine what type ecu is in the car(eprom or not), & if it is an eprom type, you need to find out what features are on the custom chip (if any) & go from there . . .

 

[marshall13]

Thanks for all the input. I had the guy who built the car do a spec list for me so I know EVERY LITTLE THING under the hood of this car. I will be sure to post a pic of the list in my profile when I get it. Meanwhile, my fuel has gone to crap.

I can't make the car go past 2,000 rpm now without leaning out completely. It will barely start, and when it does it idles like crap. I changed out the fuel filter, put in some Sea Foam, cleaned out the rail and it still won't flow. I have to do a fuel pressure test still, but I'm out of ideas unless the ECU (whatever it is) is taking a dump and isn't sending the right info to the pump.

 

[marshall13]

Okay, found out that the ECU is a stock 2G ecu, and the CAS is stock 1G. Nothing is there to regulate the misfires. I will now be getting a DSMLink. Oh, and I also ordered a new fuel pump for the other problem. Thanks a lot for the help.

 

[marshall13]

Oh, and what type of 1G CAS should I be using if I get the DSMLink and ECU? Also, if I go with an EMS from AEM, I shouldn't need the DSMLink should I? It has the datalogging built in, but I don't know if it will help eliminate the misfire.