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Topic: Troubleshooting persistent misfire (Read 1934 times) previous topic - next topic

Re: Troubleshooting persistent misfire

Reply #60
You have a stock cam in it right? Personally never had an issue but I also know all cams are different from one another. Is it possible yours is different enough to cause an issue, maybe but seems unlikely. Youre right though putting a degree wheel on it is the only way to know for sure but seems like a long shot to me. I personally would start with different plugs cap and rotor the maintenance stuff that has to be done eventually anyway. Cant say I've ever had a set of plugs last me more than a year even when I was N/A, now days I go through a set of ngk 5673-7 in about 3 months at most.  I would also try and set base idle by unplugging the battery and clearing KAM unplugging the IAC reconnect battery starting it and adjusting the throttle plate until it idles where I want then shut it off and plug the IAC back in start it and let it run for a while sometimes Ive had to do it a few times after replacing my throttle body to get idle back to normal. You said it acts up at 2000 rpm right? Like its misfiring?

The cam that came out of a factory '89 Mustang longblock, yes. Originally had that with the topend from a '93 Cobra, and this A9P. I've been through various engine builds since then, with at least 3 plug wire sets, maybe 4 or 5 sets of plugs across the heads, 5 injector sets (three different 19lb sets, a 24lb, and a 30lb), 3 full distributors, 2 MAF sensors, 3 IAC valves, 3-4 EGR valves, 3-4 alternators, 3 batteries, a few new replacement engine and coolant temperature sensors, and who knows what else.

Kinda wish I just had an aluminum DART 351 block instead, machined from scratch and internally balanced...a fresh build.

I'll have to get a new parked video recording when I have some daylight.

On another note, my switching 5v regulator is arriving soon and I'll finally get the cluster's mechanical regulator replaced. Those three gauges have also annoyed me forever.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #61
I'm going to agree with Outsidedog. I highly doubt it's the cam timing. Every stock Ford 302 on the assembly line just had the HO cam installed dot to dot and they ran fine. It has to be some crazy electrical issue. Was the cars harness ever "worked on" before you bought it?
88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, bunch of other stuff.

Re: Troubleshooting persistent misfire

Reply #62
Car has been in the family since 1991. It ran perfectly smooth with the stock powertrain, up until I swapped it out with the completely new motor. Has never idled correctly since.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #63
Still going to get you that datalog of my spark at idle this weekend. But until then I have more questions, what AFR are you shooting for at idle? are you hitting it? and when was the last time you calibrated your wideband sensor?

Whats your fuel pressure at idle and what does it change to when you pull the vacuum line off the regulator?


So you have an A9P running on a 4r70w. Which controller are you using to control the trans?

Sorry for all the questions there's just such a wide range of things that can affect idle quality and trying to give you any sort of good idea without being there is difficult.

Re: Troubleshooting persistent misfire

Reply #64
Still going to get you that datalog of my spark at idle this weekend. But until then I have more questions, what AFR are you shooting for at idle? are you hitting it? and when was the last time you calibrated your wideband sensor?

Whats your fuel pressure at idle and what does it change to when you pull the vacuum line off the regulator?


So you have an A9P running on a 4r70w. Which controller are you using to control the trans?

Sorry for all the questions there's just such a wide range of things that can affect idle quality and trying to give you any sort of good idea without being there is difficult.

The AFRs are simply switching around lambda, I run 92 octane "up to e10/whatever they have in the pump" sometimes, sometimes 92 octane e0. I have mostly the 92-octane from a chevron a few blocks away in there right now. Of course it's hitting lambda if the narrowband o2s are switching.

I haven't touched the wideband in years, but I do have a second new gauge-less one to install here soon in the passenger side. I've had an old aem thing in there that requires the gauge, and outputs the signal line from the gauge. Driver side has the Innovate LC-2 screwed ion.

FP was mentioned earlier - it's 33psi with 16in of vacuum, 39psi with vacuum detached. I'm going to play with some random tune settings this weekend to see if ANYTHING gets the idle any smoother.

4t70w is running from the original Baumannator TCS. Don't remember if this trans went in with the motor in the mid 2000's, or if I briefly ran the aod. I've had the 4r in there since before the Quarterhorse though, and likely before I ran a TwEECer.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #65
Car has been in the family since 1991. It ran perfectly smooth with the stock powertrain, up until I swapped it out with the completely new motor. Has never idled correctly since.

I guess it could be mechanical (cam shaft) but it just doesn't seem likely. Just swapping engines shouldn't screw with the electronics, unless some wiring got pinched/cut in the process. It just seems light a giant PITA to degree the cam and put a carb intake on for testing if it doesn't solve the problem.
88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, bunch of other stuff.

Re: Troubleshooting persistent misfire

Reply #66
Agreed on the pita, but carb is easy if you already have the intake pulled. Just re-use the old gaskets with rtv for the test, and new gaskets when reinstalling the efi intake. Degreeing the cam, I'd just advance it while in there already. I'd completely swap the cam if I wasn't worried about ptv - don't want to pull the heads. The motor has a ton of ptv clearance right now though - lots of clay thickness when I tested it during the head install.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #67
What pistons are in the engine? If you've got the HO style pistons and TW heads you probably have miles of clearance with most off the shelf cams. Heck a local guy has an 86 Thunderbird he put a TW top end kit on. With the stock 86 Thunderbird flat top pistons (engine and whole car had 8600 miles on it when he did the swap) and a TF Stage 1 cam he had miles of clearance.
88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, bunch of other stuff.

Re: Troubleshooting persistent misfire

Reply #68
Yeah, they're stock-like. TRW-L2305F30 pistons.

Block was 0-decked and TW170 heads were milled .030 to get 54c chambers. With those and the HO cam, there was loads of clearance when I checked. The clay looked to have almost as much as 1/2 inch - I didn't measure exactly as it was simply thick.

I am happy with the HO cam, if I could get the shortblock to run smoother at idle. Don't care about getting every last bit of power from the motor (even +30hp), it already moves fine with the parts it has. But if I were building a new shortblock today and knew I wouldn't have ptv clearance (clay), of course I'd try a different/newer style cam that's a bit more aggressive. I'd also run a completely different longblock, and wouldn't be cheap. Then I'd probably still have idle issues and hate driving the car.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #69
Weird I swear I looked through all the posts and didnt see a thing about fuel pressure.
Maybe try tuning it, you have all the equipment, force OL and recalibrate the afr sensor and adjust your MAF transfer until your open loop fuel table and AFR gauge agree with each other after the engine is warm. Maybe its just not happy because its getting more airflow than its expecting because you have a 306 with tw heads and a gt40 ported intake running on a stock tune. I mean im sure people have done it, but every single engine is different from each other not one tunes the same as the other. You could also tune the Idle but thats more difficult to walk through without being there and seeing the data, the link I sent earlier from efidynotuning is probably the best info on tuning idle Ive found anywhere.

Re: Troubleshooting persistent misfire

Reply #70
Yeah, I want to throw fuel at it again. When I did this weeks ago, it didn't clear anything up, but I was also on the dying coil. Need to re-do some tests.

Install second LC-2 wideband in passenger bank and hook up to DataQ, setup in BE, run engine until CL and make any adjustment if necessary to get wideband map closer, disable CL and mess with either injector values or MAF depending on which settings look like they'll be the correct correction, richen mixture a point and see if anything smooths out. Mess with timing and see if anything smooths out. Run car without alternator to see how it is on a fixed DC Voltage from the battery. Run second EEC-IV ground from battery to EEC.

These are some of the things that I'd like to perform and (re)test tomorrow. Simple tests out of the way.

The stock tune reading the stock MAF should be pretty dead-on though, with the factory tune. Stock airbox. Airflow metering should be accurate between it or the PMAS/Pro-M MAF.
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #71
Airfliow may be close but without an accurate wideband reading we wont know you'd be tuning in the dark. How are you going to set up the wideband in BE I have mine hooked to the EGR output and adjusted the transfer function accordingly. But you're still running an EGR right? I run an innovate LC-2 w/gauge haven't used the dataQ yet. Disconnecting the alternator is a good idea maybe see if your datalog signal cleans up still a long shot but worth a look.

Re: Troubleshooting persistent misfire

Reply #72
The Wideband(s) are on a DataQ. I have the EGR blocked off right now, but also have never used it for o2 input. Hardwired via analog lines in DataQ only.

I just need to look at the spec sheet and reset the wideband map to factory range, check again, and adjust as needed to get close to the switching from the narrowbands (a bit above and below lambda of 1).
1988 Thunderbird Sport

Re: Troubleshooting persistent misfire

Reply #73


Heres my spark at idle, Its brief because I have more oil to clean up turns out. Also while you're tuning bump your base idle up 100 rpm and see if it smooths out at all.


Just so you know my tune is always open loop. I did that so I can lock the fuel and timing in and don't have to worry about the computer trying to adjust when I'm about to hit the nitrous. I always know what spark and fuel I should be at for any given Load.