at WOT, engine bucks and spits

[LIRS6]

I wil do some pressure testing tomorrow; System/Cold Control/Warm Control/Residual, but in the meantime thought I'd throw my issue out there in case there are suggestions as to what else I should be checking. As the title says, at wide open throttle and at about 4K RPM's, the engine starts to spit and buck a bit .. spitting/catching ... spitting/catching...

- Car is '79 US with WUR 045 - shows 24.4 ohms resistance at ambient temp 71 F/21.7 C
- 10K ago; New injectors/fuel filter/fuel accumulator
- Original fuel pump
- Fuel; premium only, name brands

Thanks for any ideas ..

Jason

[AndrewCologne]

Did you set the CO in the recent past? Often people just forget pulling the allen key afterwards.
This prevents the air flow sensor plate lever from a free movement.

[LIRS6]

Originally Posted by AndrewCologne

Did you set the CO in the recent past? Often people just forget pulling the allen key afterwards.
This prevents the air flow sensor plate lever from a free movement.

No, but I’ll check plate movement as well, thanks.

Jason

[LIRS6]

Posting pressure test results:

79 SC
US
WUR : 045
Ambient temp: 21.8 C
WUR resistance : 24.3 ohms
System pressure: 5.0 Bar
Cold Control Pressure : 1.9 Bar
Warm Control pressure : 2.6 Bar max (2.5 mins)
Residual Pressure :
Start : 2.25 Bar
5 mins : 1.6 Bar
15 mins : 1.5 Bar
30 mins : 1.4 Bar
60 mins : 1.1 Bar




Color of fuel :



I added the fuel photo because I’m wondering if it looks off color (93 Octane).

Warm Control Pressure looks a tad low - Is that at the WUR? I have a WUR previously purchased from Tony that can be adjusted. Play with that?

Getting back to the topic, what next to check regarding cause of hesitation at WOT?

Thanks in advance

Jason

[john walker's workshop]

Fuel filter? Take it off and blow through it.

[LIRS6]

Originally Posted by john walker's workshop

Fuel filter? Take it off and blow through it.

Noted John, thank you - I will do that tomorrow am and revert. Fyi filter is about 3 yrs old.

Anyone think gas looks odd?

Jason

[76FJ55]

My first thought was fuel filter also, but I concur the fuel does look a bit darker than I would anticipate.

[john walker's workshop]

Yeah, odd color for sure. Maybe it's the proverbial "Bad Gas".

[MStier]

Remember, gasoline right out of the refining process is clear. The manufacturers add color to distinguish among grades. Mid-grade is normally yellow, high-test pink. But gasoline does oxidize as it ages, and that apparently turns it brown. The color of your gas looks to me to be a little brownish, so it may well be bad gas. When did you last fill the tank? And did you do so at a reasonably high-traffic gas station?

[LIRS6]

Originally Posted by MStier

Remember, gasoline right out of the refining process is clear. The manufacturers add color to distinguish among grades. Mid-grade is normally yellow, high-test pink. But gasoline does oxidize as it ages, and that apparently turns it brown. The color of your gas looks to me to be a little brownish, so it may well be bad gas. When did you last fill the tank? And did you do so at a reasonably high-traffic gas station?

Thanks for your comments - my most recent fill-up was 2 weeks ago at a brand station on Long Island, and yes high traffic. I had been driving the car for several months without issue.

Jason

[AndrewCologne]

Originally Posted by LIRS6

Posting pressure test results:

79 SC
US
WUR : 045
Ambient temp: 21.8 C
WUR resistance : 24.3 ohms
System pressure: 5.0 Bar
Cold Control Pressure : 1.9 Bar
Warm Control pressure : 2.6 Bar max (2.5 mins)
Residual Pressure :
Start : 2.25 Bar
5 mins : 1.6 Bar
15 mins : 1.5 Bar
30 mins : 1.4 Bar
60 mins : 1.1 Bar

A warm control pressure of 2.6 is too low – should be about 3.5 bar.
Did you pull the vacuum hose at the WUR when reading the pressure?
Cause if not then at WOT per design the vacuum will be significantly reduced which causes an additinal AFR drop and ... a far too rich combustion a WOT.

Beside of the case that you fuel maybe is the guilty one, you really should take care of the warm pressure and ... after that ... a proper CO adjustment at warm engine state.

[john walker's workshop]

Plugged cat?

[LIRS6]

Originally Posted by AndrewCologne

A warm control pressure of 2.6 is too low – should be about 3.5 bar.
Did you pull the vacuum hose at the WUR when reading the pressure?
Cause if not then at WOT per design the vacuum will be significantly reduced which causes an additinal AFR drop and ... a far too rich combustion a WOT.

Beside of the case that you fuel maybe is the guilty one, you really should take care of the warm pressure and ... after that ... a proper CO adjustment at warm engine state.

Thanks Andrew, agree WCP. Pressure was measured with engine off, so no vacuum. WUR is out for testing/re-calibration, ditto injectors. Will drain tank, replace fuel filter and put all back into place next week after parts are back.

Jason

[LIRS6]

Originally Posted by john walker's workshop

Plugged cat?

No Cat - SSI’s into Dansk muffler (thank you NYS).

Jason

[Dave Kost]

Put a timing light on it. Is the ignition timing advancing? Check for a strong spark too.

[Paulporsche]

Did you check your warm control pressure with the engine running?

Have you checked for vacuum leaks?

Have you verified that all your ignition components (plugs, wires, cap, rotor, distributor) are all working correctly?

Have you checked your mixture (CO%)?

[LIRS6]

Originally Posted by Paulporsche

Did you check your warm control pressure with the engine running?

Have you checked for vacuum leaks?

Have you verified that all your ignition components (plugs, wires, cap, rotor, distributor) are all working correctly?

Have you checked your mixture (CO%)?

Not as yet.

[LIRS6]

Originally Posted by john walker's workshop

Fuel filter? Take it off and blow through it.

Blew through it - lots of resistance.

Now my dilemma; I am trying to replace fuel filter Bosch 0 450 905 016, but having difficulty sourcing it. I thought I had found this unit, but was sent Bosch 0 450 905 021 - the fuel fittings do not fit into one of the ends of the filter.

How have others dealt with this issue? Again, my car is a US ‘79SC with original 3.0 engine.

Jason

[john walker's workshop]

Find a 003.

[LIRS6]

Originally Posted by john walker's workshop

Find a 003.

John - i have always admired and respected your intuitive skills and your willingness to
share/answer questions. Having just returned from FLPS with an 003 as a recourse, I was about to float the question here if an 003 is an acceptable alternative and there you were with
answer in hand. BINGO! Fittings are correct, length of filter slightly shorter but it should fit fine.




Many thanks John.

Jason.