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kurgan

kurgan

Active Member
Posts
638
Location
Aberdeenshire
Quick question. My 98 D1 V8 has a just had a new generic Y-pipe with cats fitted and lambdas for MOT.. It passed.
But the car is now struggling to accelerate and select gears and it's vibrating when engine is on. Feels like it's making too much pressure in the exhaust but also feels restricted flow i.e. like it needs to burp. Idle is lumpy and not at all smooth. Same thing in Park/Neutral as well as in Drive. Can this happen with a new exhaust? Or is it something else. Any ideas? Thanks in advance. Anyone in the Aberdeen area that could come and take a look and see what it is.
 
It a first i’ve seen mentioned that an after market exhaust system giving issues. Anything else been touched?

Ok start with the ignition system, are all the plugs firing, are the connections at the coil good, as anything elect been touch. Misfire will give a vibrating engine more so at idle with a V8 also is there exhaust joint leaking, crankcase filter clear, air filter clear?
The vehicle needs to move and with an engine without issues for the gear box to select the ratios smoothly, so don’t worry about the gear box, concentrate on the engine.

Unfortunately I don’t understand this “ Feels like it's making too much pressure in the exhaust but also feels restricted flow“. is that the same as blocking the gasses at the tailpipe and the engine eventually stops? I don’t know what that feels like either:(
 
discool said:
It a first i’ve seen mentioned that an after market exhaust system giving issues. Anything else been touched?

Ok start with the ignition system, are all the plugs firing, are the connections at the coil good, as anything elect been touch. Misfire will give a vibrating engine more so at idle with a V8 also is there exhaust joint leaking, crankcase filter clear, air filter clear?
The vehicle needs to move and with an engine without issues for the gear box to select the ratios smoothly, so don’t worry about the gear box, concentrate on the engine.

Unfortunately I don’t understand this “ Feels like it's making too much pressure in the exhaust but also feels restricted flow“. is that the same as blocking the gasses at the tailpipe and the engine eventually stops? I don’t know what that feels like either:(
Click to expand...
Hi Discool, thanks for the reply. The car only had the Y-pipe and lambdas replaced. The air filter was the only other thing to be replaced. What I was trying to say regards the restricted flow was I try and accelerate it feels like I'm pushing against something that won't let the car breath freely. If that makes sense
 
kurgan said:
Hi Discool, thanks for the reply. The car only had the Y-pipe and lambdas replaced. The air filter was the only other thing to be replaced. What I was trying to say regards the restricted flow was I try and accelerate it feels like I'm pushing against something that won't let the car breath freely. If that makes sense
Click to expand...

So where/When did the Cats come into this?
Are all the plugs to the lambdas good?

J
 
kurgan said:
Hi Discool, thanks for the reply. The car only had the Y-pipe and lambdas replaced. The air filter was the only other thing to be replaced. What I was trying to say regards the restricted flow was I try and accelerate it feels like I'm pushing against something that won't let the car breath freely. If that makes sense
Click to expand...

Ok, when I fitted a Janspeed cat back system and on starting my engine idle speed when up to 2500 rpm or there abouts which to me indicates the enging is breathing better, anyway the revs stayed the same for a couple of minutes and then started dropping down and it does normally with a cold start to arround the normal 700rpm.
All that indicates that the EFI ECU is re adjusting as it should.

Anyway not a solution unfortunatlly, but wondering if your EFI readjusted it self in anyway, after fitting the cats and the two Lambda's sensors are correct and compatable and seen by the ECU.
With that in mind i'd check out the part numbers. I never had to go there with Lambda's but assume that the connections are still in place what ever they are. If you could disconnet the battery for a minute so the the ECU restores to default, then reconnet and the ECU will find a suitable setting for the engine after restarting the engine.
 
discool said:
Ok, when I fitted a Janspeed cat back system and on starting my engine idle speed when up to 2500 rpm or there abouts which to me indicates the enging is breathing better, anyway the revs stayed the same for a couple of minutes and then started dropping down and it does normally with a cold start to arround the normal 700rpm.
All that indicates that the EFI ECU is re adjusting as it should.

Anyway not a solution unfortunatlly, but wondering if your EFI readjusted it self in anyway, after fitting the cats and the two Lambda's sensors are correct and compatable and seen by the ECU.
With that in mind i'd check out the part numbers. I never had to go there with Lambda's but assume that the connections are still in place what ever they are. If you could disconnet the battery for a minute so the the ECU restores to default, then reconnet and the ECU will find a suitable setting for the engine after restarting the engine.
Click to expand...
discool said:
Ok, when I fitted a Janspeed cat back system and on starting my engine idle speed when up to 2500 rpm or there abouts which to me indicates the enging is breathing better, anyway the revs stayed the same for a couple of minutes and then started dropping down and it does normally with a cold start to arround the normal 700rpm.
All that indicates that the EFI ECU is re adjusting as it should.

Anyway not a solution unfortunatlly, but wondering if your EFI readjusted it self in anyway, after fitting the cats and the two Lambda's sensors are correct and compatable and seen by the ECU.
With that in mind i'd check out the part numbers. I never had to go there with Lambda's but assume that the connections are still in place what ever they are. If you could disconnet the battery for a minute so the the ECU restores to default, then reconnet and the ECU will find a suitable setting for the engine after restarting the engine.
Click to expand...
discool said:
Ok, when I fitted a Janspeed cat back system and on starting my engine idle speed when up to 2500 rpm or there abouts which to me indicates the enging is breathing better, anyway the revs stayed the same for a couple of minutes and then started dropping down and it does normally with a cold start to arround the normal 700rpm.
All that indicates that the EFI ECU is re adjusting as it should.

Anyway not a solution unfortunatlly, but wondering if your EFI readjusted it self in anyway, after fitting the cats and the two Lambda's sensors are correct and compatable and seen by the ECU.
With that in mind i'd check out the part numbers. I never had to go there with Lambda's but assume that the connections are still in place what ever they are. If you could disconnet the battery for a minute so the the ECU restores to default, then reconnet and the ECU will find a suitable setting for the engine after restarting the engine.
Click to expand...
I'll give that a go. Nothing to lose.
 
Sounds intriguing. I suspect there is something simple not playing the game. If it passed MOT emissions the engine is fundamentally sound. The cat test does two measurements, idle and fast idle although there is no load.

Maybe a little obscure but at this time of year depending on weather/temperature it is not unknown for condensation to form inside the distributor cap, this can cause misfires and loss of power. It could also be the case the ignition system needs fettling. Have you checked the condition of dizzy cap and rotor arm?

If you suspect an exhaust restriction, try doing a vacuum test it should show up. Good luck.
 
classic kev said:
Sounds intriguing. I suspect there is something simple not playing the game. If it passed MOT emissions the engine is fundamentally sound. The cat test does two measurements, idle and fast idle although there is no load.

Maybe a little obscure but at this time of year depending on weather/temperature it is not unknown for condensation to form inside the distributor cap, this can cause misfires and loss of power. It could also be the case the ignition system needs fettling. Have you checked the condition of dizzy cap and rotor arm?

If you suspect an exhaust restriction, try doing a vacuum test it should show up. Good luck.
Click to expand...

Thanks, dizzy cap and rotor arm look ok. How would I do a vacuum test? When I revv the engine it starts to pop (like backfire) then it cuts out completely.
 
Vacuum test is quite easy. First get yourself a vacuum gauge. You'll need to attach the gauge to the plenum, I pull the vac pipe for the heater on my RRC, not sure if there is a suitable vac port on a D1 but would think there may be a blanked off port you could use. Do not use the vac line to the distributor, this is ported vacuum and only shows vacuum when the throttle is opened.

Start the engine and then look at the vac gauge. Depending on what it shows and whether or not the needle fluctuates will indicate if anything is wrong. Essentially you want to see a steady needle with a reading somewhere between about 18" to 21" of vacuum IIRC. Mine pulls less, about 15" at idle but it has a different cam and 4 branch headers with a pair of straight through cherry bomb silencers.

It is interesting what you say about it popping when revved. Makes me think you need to look at the ignition timing and also the vac advance unit. An inlet air leak may be a possibility so a vacuum test might be useful in identifying it if that is the case.Either way I don't think the problem is terminal.
 
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