Still Lean?

C

Campbell

New member
Just finished my last event with my third engine.. (84 Scirocco ITB) the practice session went great! for the first time this year the car great in that session - good temp, fuel mixture and oil pressure. The gremlins returned in qualifying: I had pulled the radiator fan assembly since the ambient was so cool and temp seemed not to be an issue. 4 laps into the session the temp ran high, the overflow tank was blowing fluid which was hitting the tires.. I thought it was because I had taken the fan off so I reinstalled it for the race.

Didn't complete the first lap in the race -- overheated again and it sure reminded my of the first engine loss I had this season, I melted the pistons by running lean. I pulled off as the overflow tank was blowing fluid again. Diagnosing the first engine was tough because the ignition distribitor was going at the same the fuel pressure controller was failing, ugh. Brand new distributor on the car now. When I got the car home I hooked up the dwell meter to read the freq cycles (I had the car set very rich with the set screw, the freq was only at 15 to 20 cycles at idle if it even came on, the full throttle switch runs the freq cycles to 60). As it idled at 15 it would suddenly stutter and begin to run lean, either severly with the freq cycles going to 90 or mildly with the freq cycles jumping to 50 or 60 and then it would drop back to 15. I hooked up the fuel pressure gauge and it was locked on 51 lbs pressure the no matter how it leaned out. I did determine the fuel pressure controller was faulty on the first engine failure - replaced both it and the fuel distributor (both used) and the issue cleared up. I think I was running lean again which caused the overheating - it wasn't as severe as last time since I was running much richer at the fuel distributor this time. Do you think I had a second fuel pressure controller failure? twice in a season? anything I am missing on this? thanks I will look for a new controller this time. Any ideas on what else to check would be appreciated.
 
Man Bill, this thing just won't play nice will it? It was great to see the car running so well on Saturday. I don't suppose you had some boilover approaching 3d today?

Anyhow, as you know the two best culprits are lean fuel, or too much timing. Since the distributor is new, it is probably OK to assume timing is what you intend. I still think you are in a position that you have to find some dyno time. There is anther dyno in our area that should be more receptive to you than the last one. Shoot me an email and I will get the info to you (don't have it handy right now or I would post).

I seriously hope that you did not do any damage.

Also, I am sure that none of your engine temp issues were related to the fan being there or not. It was just way too cold for that. However, how about the rest of the cooling system? Pump, thermostat, radiator, etc. Any chance some of that stuff is defective?

Keep me posted on what you find and I will try to help.
 
If it is a 2nd bad fuel distributor, keep in mind that they usually fail because of debris in the fuel. The debris often originates in a rusty tank, and can get pushed through the pump (causing increased wear). If the filter isn't changed in time, it may partially fail and the debris actually gets pushed through it too, and on to the fuel distributor and injectors. I once had a car with this problem, and managed to preserve the hard parts by installing a pre-filter before the main pump (a tight fit, BTW). The pre-filter filled up fast, but the main pump changed its tune to let me know when to change the pre-filter. That older car did not have a pre-pump, but wasn't used for racing either. My guess is that it would have starved more easily in right-hand turns if I had raced it.

Edit: If your car is a later 84 WITH the pre-pump, these often fail too. The screen may get clogged or the pump itself may fail from a defect -- there was a recall or campaign at one time). The car may still run with a failed pre-pump (since it's already primed), but it puts a much greater load on the main pump and can cause lean running.

BTW, I've learned not to rely on fuel pressure readings since they can't indicate flow volume. On that note, the CIS systems all run lean if there's any restriction in the RETURN line to the tank (anti-intuitive, I know, but that's the way it works).
 
Here is a dumb question, I just don't get this: If the fuel pressure is constant at 51 lbs and the car is exhibiting lean to rich running conditions (based on the freq valve response and air fuel mixture gauge) how can the warm up regulator be bad? system pressure is 72 lbs and it is controlling it to 51 lbs with no variance.. wouldn't you think the fuel distributor is to blame? thanks
 
I've never actually seen a bad warm-up regulator (more accurately, control pressure regulator). If it's not leaking, and if you haven't overdone the enrichment by pushing in the pin too much, there's really not much that can go wrong with them. Pushing in the pin reduces the total control pressure, but should not affect the difference between the cold and warm control pressures, AFAIK. It's only job is to gradually increase control pressure a bit as it warms up, thereby leaning the mixture a bit as the car warms up. It's just a very simple bi-metallic spring inside (unless you've got one that hooks to vacuum or attempts to compensate for barometric pressure). The electrical connection/heater part of it really doesn't matter much unless you're doing emissions testing from a cold start with a stopwatch.
 
I would add a cheapie air to fuel ratio gague and just tap the signal off the stock 02 sensor. On my g-60 corrado its not really precise enough to tune by, but its more of an idiot light of sorts. if the gauge pegs lean then you know you have a problem and let off the gas and figure out what has went wrong. Since the jetronic box is just there to adjust the aux air valve and other emissions related stuff tapping the signal off of the stock O2 sensor wont be enough to skew things. On some later EFI cars tapping the stock O2 can cause problems (had a bad gauge wreak havoc on my corrado fwiw). Since the jetronic box is very basic and its primary functions are emissions related and its a track car i wouldnt worry about it. :)
 
I hope to start troubleshooting the lean issues tomorrow. I have been thinking, I would like to monitor the frequency valve inside the car while driving. Is there anything other than a dwell tach meter that would give me a reading? I could run wires into the car from the test port but don't want to strap my dwell meter to the dash, it is kind of big.

Open to suggestions, thanks
 
I had this problem when I put a new head on the GP car. It would idle and run in the paddock just great, but as soon as I started to get it to rpm's and speed, I also would blow out the water and it would run hot.

Turned out it was a cracked head.

Sorry to offer some bad ideas.
 
Finally I was home long enough to check some things out.. I had done every fuel system test but one and everything had checked out fine which was frustrating. I just did the fuel pump flow test last night.. the current pump flowed 15 oz in 30 secs (not sure of the volt draw at the pump because I was doing this by myself). The flow seemed very weak, the Bentley said it should be 30 oz with a strong battery draw. I switched to a used Bosch back up pump and re-did the test: it flowed 25 oz in 30 secs, there was a very significant change in flow velocity between the two. It was late so I couldn't start the car up to see how it runs, I will try to do that over the next couple days. I think I may have the lean condition culprit. If I could do rubic cubes I could understand how you can have acceptable pressures, which I did, but have unacceptable volume - which I had. I also agree with Racer Tim that I probably have a cracked head which is pressurizing the rad at high rpm - if the fuel system now behaves the head comes off next to get checked out.
 
Actually thats highly possible and happens all the time when people are throwing turbos on motors and forget to ensure that the fuel pump can flow enough gallons per hour.

So likely your pump is having some internal issue where it could create and hold the pressure but could not flow enough rate. 50% less flow then nominal is not very good at all.

Let us know how that turns out.
 
Started the car up this afternoon and was hoping the new pump would make a difference, it did kinda.. it started off doing the full lean thing (going full 90 cycles) and then back down when I took it up to 2000 rpm. After 10 minutes or so it quit doing it doing it chronically - that is the improvement. The car still ran lean and had a difficult time idling however at slightly elevated rpms, 1800 to 2000 the fuel system would operate normally. The valve cover blow by was blowing white smoke, when I pulled the hose off I am having a lot of blow by and it is blowing radiator fluid. Obvously my issues are far from fixed. I have decided to pull the head and figure out what is going on - get the basic engine integrity straight and then address the fuel problems. Possibly the fuel issues are impacted by other issues. I think Racer Tim's comment on a cracked head may be it or I screwed up the head gasket when it got hot.

I will keep you posted on what I find when the head comes off. thanks
 
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