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ECU Fault Code 1251

2K views 29 replies 6 participants last post by  LawrenceJuliano 
#1 ·
My '91 S4 Spider is showing a CEL code of 1251, which I gather is ECU fault. From what I was told, this CEL didn't appear until the previous owner put the original intake back on in place of a horrid K&N system. The original intake hose was split, so I replaced it with a brand new one, but the CEL still appears (strangely) every couple of times I start the car.

Should I go down the path of getting a replacement ECU, or is there a simpler fix? Could it be false air or is there a way to reset the ECUs in these cars?

Also, I get all the warning lights popping up / flickering in the dash on very rare occasions, this goes away with a quick rev. Very strange.

Thank you

Lawrence
 
#3 ·
Thank you, I'll have a look at that.

Drove the car today, and as usual the check engine light only comes on (like clockwork) every other time I start the car.

I hope somebody can provide some insight to this, I'd be happy to order a new ECU, just don't want to jump the gun if it could be something simpler.
 
#4 ·
When the car is first turned on, the brake and coolant warning lights come on for a few seconds (this is done via the intermittent wiper timer relay.) If you lose electrical power while driving, these lights will come on again.

If those are the lights that are coming on, it's probable you're losing system power. This could possibly be causing an error in the ECU.

Overall power loss could be a bad ignition switch, or alternatively loose connections at battery, battery ground to body, alternator, starter, junction box in engine bay left side fender, or at fusebox. Make sure you disconnect the battery before messing with any of these as most of them are +12V hot.
 
#7 ·
I reset it this morning and it returned the next time I started the car. Today it started becoming hard to start and runs on for a couple of seconds after the ignition is cut.

I think I might just bite the bullet and send the ECU out for repair, or buy another if I can find one.
 
#10 ·
So, quick update. I had my mechanic replace the in-fuel tank pump today, and afterwards he tried another ECU. The new ECU cleared the CEL, but strangely the car ran just as well as it did before. Sadly, the run-on remained, so he looked into the timing. Things got very strange when he found that the timing at the distributor showed as majorly off, where 4 should have been at 1 (I'm sorry, I understand the basics of timing but don't want to get too specific as I may confuse things). When he put in another distributor and put the timing to where it should have been, the car missed and ran awfully, as if it was completely off timing. He had no explanation as to why the timing would show backwards but the car would run perfectly.

I walked away today with little to no answers, but only guesses. My suspicion is that nothing is wrong with my ECU, and that it was modified (there are markings on the top casing along the lines of "8-21-03 Phase 1"), which is why the system shows fault. Would a squadro chip cause this? The PO spent some proper money on the car, the suspension, shocks, etc have all been upgraded including chassis stiffeners and an ANSA exhaust.

So now I stand with no answers on the ECU and little to no idea as to why it is running-on (outside of a possible ignition switch issue, which I have my money on, but my mechanic says is not the issue).
 
#13 · (Edited)
He had no explanation as to why the timing would show backwards but the car would run perfectly.
...that just means the timing is 180° out. Someone has put the engine back wrong (;)), but it'll work fine.

not sure what the 'phase 1' means on the ecu. The squadra chip (if fitted) shouldn't cause the problems you seem to have. Lots of S4 owners in europe have it fitted. Generally squadra do not mark the ecu, it is just the chip inside which is exhanged.
Of course, make sure you have the correct ECU, correct Bosch number for the S4.....
Bosch 0 261 200 124
 
#11 ·
My 86 had the distributor put in 180 out, also. We can do that on these engines; just move the plug wires around to match lol. I was down for two weeks once, when after I did my first tune up with wire replacement, it wouldn't run. This forum helped me figure it out.

So with the run-on, does it run normally then finally shut off? or does it sputter like an old Nova until it finally dies?
 
#15 ·
the run on (1,5-2 seconds), does this happen on a cold engine too? or only when really hot after a run?
sounds like fuel leaking into the chambers and igniting, but I can't imagine it would ignite on a stone cold engine...
I wonder if one of the injectors is leaking slightly? (the S4 doesn't have a cold start injector like the S3, so no need to worry about that)

tried running some injector cleaner? like Techron....you never know....
 
#17 ·
To get run-on with a fuel injected engine is difficult. When you turn the key off you turn off both the injectors and the ignition, so there's neither fuel nor spark. That's why I was wondering about the ignition switch: given you had possible power loss issues while driving (which can also be caused by the switch) it's possible the switch may be faulty and not be fully going open circuit or something when you shut it off. I realize it may be a bit of a stretch, but between that and the warning lights coming on while driving you've got some weird problems.

Assuming the switch is actually cutting power, run-on would need to be a combination of leaky injectors and hot spots in the combustion chamber causing ignition. As suggested above, a bottle of Techron (the larger size one) would be a good place to start.
 
#19 ·
I'm confident that you're correct about the ignition switch, I'm going to look into testing my current one or swapping it with a new one. I checked the battery terminals, and deleted a battery cut-off tap (that wouldn't get tight enough for confidence) that the PO installed on the negative terminal. Sadly, this didn't cure the power loss issue as I had the flickering lights return a few minutes ago on a quick drive.
 
#18 ·
Not as familiar with S-4 as S-3. but here goes. Timing 180 out on the distributor is the drive, part of the oil pump, incorrectly installed, as the distributor only goes in one way (offset slot) as noted, move the plug wire on the cap.
I wonder if either of both: incorrect drive relay (should be BOSCH not KAE) and some folks wire the fuelpump circuit
to the injector circuit at the ECU instead of its normal routing from the fusebox. Has your mechanic done a stone cold valve adjustment and also checked the cam timing?
 
#24 ·
You could cut the head off a live chicken......

The video of the lights is really weird. I had pictured what I think you're describing in the last post - just flickering on for a moment while the car choked. Not sitting there lit up like a Christmas tree while you blip the engine.....and your voltmeter seems rock solid and totally normal. This has got to be grounding somewhere, right?
 
#25 ·
Just past the 12 mark seems very low. Alternator output should be ~13.7, and while you'll lose a bit on the switched circuits, a volt and a half seems excessive.

I'd get a digital voltmeter and directly measure the voltage at the alternator, on the always-powered side of the fusebox, and on the switched side of the fusebox. If the first two look good and you have a lot of voltage drop on the switched side that would be another indicator that the ignition switch has problems.
 
#26 · (Edited)
one thing not right in those videos is the oil pressure gauge stuck on zero, even when you rev up....it isn't budging.

I'd check the single thin red/black wire to the sender has not unattached itself (passenger side of engine, near the starter)...if wire is attached then remove it and with IGN on, ground it and see if the gauge goes to max. If it does, you need a new sender, if it doesn't the wiring to your gauge, or the gauge itself is faulty.

http://www.alfabb.com/bb/forums/6563682-post2.html
 
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