Hi all, I am having a problem with my SPi, the fuel pump went a while back…it went on fire for those that remember…I managed to get a working replacement. However, since then my fuel use is horrendous, 100 miles…£30 of fuel. Something aint right. The backfire has always been there and it is very intermittent, but, that should not happen either.
New Relay pack fitted a year ago, it was backfiring before this.
I am stuck.
Any ideas?
Lambda sensor?
> Hi all, I am having a problem with my SPi, the fuel pump went a while back…it went on fire for those that remember…I managed to get a working replacement. However, since then my fuel use is horrendous, 100 miles…£30 of fuel. Something aint right. The backfire has always been there and it is very intermittent, but, that should not happen either.
New Relay pack fitted a year ago, it was backfiring before this.
I am stuck.
Any ideas?
Hi,
Lets see if this makes sense. If there is a leak on the exhaust manifold allowing air to get in, it would fool the lambda sensor into adding more fuel causing the poor fuel mileage. Now that you have the extra fuel and air in the hot exhaust system, would it not cause the backfiring? I hope that Sprocket agrees with this. If not, I can always learn something new about the SPI.
Ivan
I would agree, the leak would have to be on the top part of the manifold (before the sensor).
Backfire in the exhaust or the inlet manifold?
Normaly a backfire with the SPi is down to poor MAP signal for one reason or another. Fuel consumption would be diabolical. I have seen several cars driven like this without MAP signal. The ECU tries to adapt, and does a bloody good job, but its far from right.
The only other thing I can think of is that if it is an early SPi, it might be the throttle pedal switch. This can cause drivability problems that come and go, and backfire is one of them
> Backfire in the exhaust or the inlet manifold?
Normaly a backfire with the SPi is down to poor MAP signal for one reason or another. Fuel consumption would be diabolical. I have seen several cars driven like this without MAP signal. The ECU tries to adapt, and does a bloody good job, but its far from right.
The only other thing I can think of is that if it is an early SPi, it might be the throttle pedal switch. This can cause drivability problems that come and go, and backfire is one of them
Well, lets see. I vaguely recall (it sucks to get old, memory goes first) mine backfiring some times on the intake when the MAP sensor line turned into chewing gum and collapsed where it connects to the intake manifold. Also the idle was erratic and the engine would die. It ran so badly that I did not check the fuel consumption.
It is 1994 model, should it have the throttle pedal switch?
I had 1981 Chevy Citation with an electronic carburetor and oxygen sensor in the exhaust to provide feedback. It also had an air pump that provided air into the exhaust manifold ports during cold operation (open loop) with no feed back from the oxygen sensor. Once the engine would warm up (close loop) the air from the pump was diverted into the catalytic converter through a separate pipe. In my car, the pipe that distributed the air into the exhausts ports developed a hole due to corrosion. The car drove fine while cold but once it warmed up and went into the closed loop, it would suck air through the hole into the exhaust manifold and the oxygen sensor would make the mixture so rich that the car drove horribly and the fuel consumption was unbelievable. However, I can’t remember if there was any back firing from the exhaust. It was too many moons ago!
Anyway, that is the experience I was thinking that could relate to this.
Cheers,
Ivan
The backfire is on inlet as it spits out through the filter lol! Will check the other things today…sticking it on Diagnostic to see whats goin on. I’ll let you know.
Also can get the same problems if the inlet and exhaust manifolds are not correctly lined up with the ports on the head, especially difficult if the head is modified with larger ports as you lose the alignment rings and the amount of metal on the inlet manifold is not great! Caused me severe headaches in the past when car was spitting flames out for fun.
Right…the initial diagnostic said all sensors were a pass.
However, the system did not recognise the ECU.
and when a diagnostic was attempted, fault found immediately was 0.00 V from ECU, minimum 11.00 V and that was that…£60 bloody quid. of course he agreed with me that that is immpossible as the engine was running.
Since I’ve been back I cleaned all connections, checked all fitting and found that the vapour trap connector to the manifold had perished and broken of, I have put a new connector on and started her up.
What it’s doing now is conking out at idle, it will run then die, also on overrun when it just dies away.
Any ideas?
Did he do a lambda check on the tailpipe gas?
Also meant to say, standard head, exhaust manifold. piper filter thats it…it also just backfired on start up again lol!
No, but it stunk the garage out he had to put it on the vacuum lol!
Sounds like a leak still to me, the lambda sensor itself could test out fine on an electrical test but if air is getting in somewhere it will just overfuel like mad and potentially backfire like you are seeing.
What happens if you disconnect the sensor?
Okay dokey I’ll go do the old WD40 test and see what happens.
stuck her up on the ramps did wd40 everybuggering where…no reaction, however at that angle it has not conked out so I’m thinking leak somewhere though.
Would you expect it before or after the lamda and if it was after would that make any difference anyway?
It needs to be upstream of the lambda to effect the running so anything around the cylinder head area really.
Right going to disconnect the lamda, see what happens there, then roll her of the ramps and see if it conks, if it does it has to be a leak
Okay dokey lambda off, as would expect brief pause then revs up. Reconnect brief pause revs lowered again. Going to check manifolds now.
by the way - Have you checked out your ignition system, spark plugs, leads, coil, dizzy cap, dizzy timing etc? Is the dizzy tight against the block?
right blocked up exhaust and she did not conk out! now revving at 2-2.5 and very slow to come of the revs after dipping the pedal…checked all that yesterday. It’s doing my head in lmao
