TB42E misfiring, backfiring through intake, losing revs under load

[salzgq]

Hey guys, I am having a weird problem with my tb42e on petrol/gas, and have read forum posts of people having similar issues, but haven't found the answer.

Things to know:
- Just did a body swap on the car, so wiring harness has been taken out and put in, I cannot remember if this problem was there before as I didnt run the motor for long before the body swap was done. However, the engine was washed with water as it had oil leaks.
- It is dual fuel, but problem is worse on petrol than gas
- Struggles a bit to start up, but isn't too bad
- Nothing wrong with the idle, backfires/misfires under load
- When I rev on petrol, it misfires, struggles to get the revs up and will backfire through the intake.
- I've only driven mostly on gas, and every 10mins or so, the revs will just stop and cut out, and it will backfire through the intake unless I chuck it in neutral and rev it back up and chuck it back into gear.
- I have opened up the distributor cap, no moisture inside, have also changed distributor cap. Have also checked timing.
- Checked the MAF, believe its working, but havent changed it.
- Put new spark plugs in
- Changed throttle position sensor
- Ran diagnostic codes, and code 13 came which is for the engine temperature sensor, but I checked the sensor while cold and hot and it had a resistances which was in the range specified in manuals. And voltage was coming to the connectors, think it was around 4.8v. Anyways, I changed the sensor, and cleaned up the connector and the code was gone. Now no fault codes. However, didn't make much difference. Is there anything else with the engine temperature sensor circuit I should check maybe?

I believe it is an electrical problem, I will next change the ecu and see if it makes a difference. Has anyone had this issue, and have found the solution? Cheers

[Avo]

airflow sensor??

[Avo]

also when you have changed it over have you disconnect the batttery for a bit
so the computer resets itself...

[salzgq]

appreciate the quick reply,

yeah i've looked at the airflow sensor, tried starting engine with it connected and disconnected and theres a difference, so it seems fine. Is there a better way to see if its working right?

and had to replace battery so yes has been disconnected

[Avo]

ok if you have just done a replacement or unplugged and plugged in wiring harness it has to be something along them lines....maybe earth is not good enough for the ecu,so even if you buy replacement you may be wasting money...check all earth again,all plus and sensors you unplugged and plugged again..

[dom14]

If it happens on both fuels but in different degrees, it may mean an electrical issue related to earth or ignition, assuming it is the same problem.

Other possibility is two different problems on each fuel manifesting as same symptoms in different degrees.

Going by the first one, checking electrical stuff like ignition leads, spark plugs & earths and other electrical connections may be able to locate
the issue. Follow the standard procedures to check the above things for faults. But, since you've replaced above suspecting parts except ignition leads, check them to make sure they are good.

Backfiring from intake can be due to fuel starvation. So, it is possible it is a fuel starvation issue with petrol due to fuel pressure or injector issues or fuel return valve issues etc.
Not sure what kinda LPG system you have, but I would check the converter, filter issues or mixer issues.

[dom14]

I believe it is an electrical problem, I will next change the ecu and see if it makes a difference. Has anyone had this issue, and have found the solution? Cheers

Diagnose the problem by elimination technique first, rather than throwing parts at it. It can get expensive part after part and problem not getting solved.

[mudski]

Just to confirm the issue happens on both gas and petrol?

[salzgq]

My bro is building a tb42e as well so I am just trying stuff off his, only have purchased spark plugs at the moment

Yeah backfires through the intake under load on both petrol gas, however when i rev it on gas it revs okay, but with petrol it stutters.

Will be checking earths tommorow, and the throttle position sensor again, trying brothers ecu

Cheers

[Bob]

My bro is building a tb42e as well so I am just trying stuff off his, only have purchased spark plugs at the moment

Yeah backfires through the intake under load on both petrol gas, however when i rev it on gas it revs okay, but with petrol it stutters.

Will be checking earths tommorow, and the throttle position sensor again, trying brothers ecu

Cheers

Get some MAF Cleaner and clean the Sensor. Also disconnect the Battery for at least two hours to clear the learnt codes.

[dom14]

My bro is building a tb42e as well so I am just trying stuff off his, only have purchased spark plugs at the moment

Yeah backfires through the intake under load on both petrol gas, however when i rev it on gas it revs okay, but with petrol it stutters.

Will be checking earths tommorow, and the throttle position sensor again, trying brothers ecu

Cheers

I can also point out this from my recent run-ins with my RB30 engine rebuild, particularly the cylinder head.
Worn hydraulic lifters(mechanical tappets in your case I reckon) & worn cam lobes as well as excessively machined cylinder heads can cause cam timing issues & backfire/misfire etc as a result. Once or if you rule out electrical and other mechanical issues, start investigating those ones I pointed out.

I'm not sure how critical it is to adjust tappets in EFI TB42 model(I dunno whether EFI model comes with hydraulic lifters or not), but for a carby TB42, it is an important factor on the smooth running of the engine.

[billyj]

while its important to adjust the tappets on a tb42e i doubt it the problem.

how did you set the timing? you need to unplug the aac valve and fcid before adjusting the dissy on a tb42e. failure to do this will result in the timing being retarded by approximately 5 degrees from where it should be.

you say its worse on petrol but still does it on gas, the olny time my old tb42e ever backfired through the intake was when the fuel pump was dead and it was going super lean under load. so my first thought is check fuel pressure and then check all vac hoses and intake piping on the engine side of the maf, as anny leak here will result in a lean running engine.