I got the chance to have some cheap power only runs on a Rolling Road today after I messed with the jetting on the A yesterday. Since it's been on the road ( 1000 miles in 4 weeks now ) it seems to stop dead at 70 mph ( 3500 rpm) .
The rejetting I carried out feels great seat of the pants and the rolling road showed a AFR of around 13.2 , just a little rich.
The engine is an old Pinto , comp test shows 160 psi so lower end of acceptable. I've added an Injection head and High Torque cam and it also has a 4 branch and 32/36 DGAV, so on a good day in the region of 120- 125bhp at flywheel.
Stock motor is quoted a 111lbs at 3500 ...96bhp @ 5200
Mine came out at 120lbs at 2100...80.2bhp @ 3250
Now the point is that the power stops dead at 3500, drops like a stone hence the lack of any acceleration but not down to aerodynamics as I first thought? The AFR is still good after 3500 even though the power is dropping ? To me that rules out leaning out due to fuel pressure ( stock manual pump with reg set at 4psi)
The motor revs clean off load and you can hear the second choke come in ( though in top , under load , it feels like you can't ?) .
One of my thoughts is that the distributor is electronic controlled by water temp and vacuum and aimed at economy ,couple that with the reduced vacuum due to cam change could that be the issue ?
I might have to revise the jetting though, dropped from 35 to 25 mpg
Anyone like to throw their ideas in the pot ?
Fuel supply issue?
a guy near near me had a s/block powered 34 that kept losing power when nailing it,
revved fine up to 6000 plus when stationary,
but after 3-4000 rpm under load it would lose power,
turned out to simply be a partially blocked fuel filter in the fuel line under the car,
being only partly blocked it still showed normal fuel pressure,
the owner didn't build the car so didn't know the inline filter was there,
the mechanic found it when on the ramp checking the fuel line for kinks.
13.2 is a bit lean if you are referring to wide open throttle, or did you mean at idle?
Whats the afr when the throttle is open?
It does however sound like the timing is wrong. Could be too advanced or retarded to be honest.
My Datsun has a permanent afr gauge and I also have a portable LM1 unit for sticking up peoples tail pipes :D They're pretty useful.
13.2 at approx 3500-4000 and still climbing . No tickover mixture reading , it's an auto which are fun to get readings from. You get a spike at bottom end as it shifts gears.
It also bogs badly off the line if you give it full throttl ebut that's not apparent under normal acceleration. The DGAS has a power valve and I think the lack of vacuum from the cam is bringing it in too early when you try to boot it from the line. That's usually masked on a manual as you leave at 2k upwards.
Could do with richening up a little maybe
kev. as has been said, you could go richer at WOT, plus I think you need more advance, bogging and nosing over are both signs of not enough initial and total advance.
Thanks for all the input so far. The bit I'm struggling to understand ( and why I initially put it down to aerodynamics) is that the engine will pull 6000 in first and second but only to 3500 max in 3rd ?
Does it bog down or hold back at all in 1st or 2nd?
On the rolling road did they include on the printouts an air/fuel graph? It can really help pinpoint whats causing flat spots etc
If you open the throttle normally no bogging in first or second, floor it off the line and it bogs before taking off. AFR / bhp graph to mph print out plus torque / bhp against road speed print outs .
Would be good to see those graphs if you can scan them in.
If you were local to me I'd suggest sticking my wideband up your tail pipe and go for a drive to work out whats what.
However, I think it's worth finding out what the total advance is with and without vacuum if possible
I'll try to scan them both this evening ( my scanner is a pain :( ) I'm working out the plan of attack on the APU at the mo . Checking advance is difficult as it's ( currently! ) fitted with an ESC Sierra module and it more or less make sup it's own mind what curve to giv eyou based on water temp and vac it sees. As it came off the 1.6 Economy model I think it's the first thing to hit the bin. I'm looking for a Transit based electronic dizzy longterm.
Looks like on some of those runs it gets seriously rich shortly after its opened up (but some of that might be misreading). However, if it is going up to 10:1 then thats the cause of the bogging down
EDIT - just remembered you said that the kickdown causes that spike...
The DGAV is fitted with a power valve that works on the primary choke.It comes in when the vacuum drops on snap throttle and I'm working on the idea of blanking the operation as a test to see if that is the cause of the bog. The run is done in starting in 2nd and the spike is the change up so anything below 40mph is a bit misleading ( possibly ).
They are normally calibrated weak on primary choke for economy and the power valve adds the fuel when acceleration needed .It didn't bog before I rejetted but it didn't pick up quickly.
OK, started troubleshooting the A engine today.
First off checked full throttle travel is WOT ,all good.
I've swapped out the old dizzy and gone with Cortina points dizzy and full 12 volt coil. Stuck 14' advance in ( no vac advance connected ) and it's sounding good,haven't road tested it yet .
I've used a vacuum gauge and I'm getting 17-19 reading with a rapidly pulsing needle ,raise the revs and the vac increases and the fluctuation all but stops. Worn Valve guides allowing the valves to rock ?
Snap throttle tests show the engine is in good nick (drops to 2 and snaps back to 25) and holding steady shows no drop so exhaust isn't blocked.
What's going on with the fluctuating needle though ? Cam is Injections sprts torque, higher lift but almost stock duration, with matched valves springs and valves were all reseated before fitting?
Mixed results ,picks up better off the line ,500 more rpm top end but pinking . At least that's the ignition system ruled out as the culprit.
Need to knock the timing back tomorrow and try again.Vacuum figures will drop for sure with less timing.
Progress(?) so far today . Timing knocked back to 10 btdc and valve clearances all checked , couple 2-3 thou loose but nothing else showing , cam lobes all good.
Looked at valve timing again. I remembered that the bolt on plate was a little battered and the point not as 'sharp' as it could be .I also have to see the cam timing marks in a miror as you cant see straight on. Anyway , there was a possibility that it could have been a tooth advanced so knocked it back one.
HORRIBLE!! Flat ,lost that crack as the cam comes on and not revving out through the lower gears cleanly .In top it will rev to 4000 but that's it.
While looking around my garage found another timing plate so ,once it's cooled down, going to swap that over and have another look.
Hve you got a vernier pulley on it?
I found that when I used a Kent EFI cam, the only way of getting both the timing and belt tension correct was to use one. With the tension right, none of the timing marks lined up, and it drove really flat(still with the EFI - even a decent carb like a DGAV is hopeless by comparison); fitting a vernier took about 20 minutes and cured the problem entirely. That cam and hour's work with a Dremel on the head on an otherwise stock 2.0l Capri, including the exhaust system, made the car as quick in a straight line as a 3.0l, with 40MPG on the motorway.
I love a good Pinto!
I've got the vernier pulley on order. The head and cam swap was a 'down and dirty' one , the head gasket had blown so I took the opportunity to fit these on quickly and didn't have a vernier pulley to hand at the time.
I used an FR30 on my other Pinto ,VERY similar duration ,and lift, and that runs fine.That only shows 10" of vacuum on tickover unlike this at 17-19 . With the timing retarded on this cam ( FR34) it's dropped to 15-17.
I've just ordered a new petrol pump as well .I keep looking at the power graphs and it all dies when the second choke should be coming in when in top but the mixture figures say it isn't leaning out.:confused:
I've just spoken to Kent Cams and even they can't understand it. They say that even on standard OEM timing marks it shouldn't stop revving in top .They also said the torque comes in early and flat through the range , unlike mine which is early and then starts dropping .
Rain's stopped play for today but got my new fuel pump to fit tomorrow as well now.
Well it revs ok in 1st and 2nd doesn't it? Otherwise I'd suggest valve springs
Revs out fine in 1st and 2nd. Cam is a kit with matched ,pads ( followers ) springs and retainers , it's only the box shifting ,at 6000 !!, that stops it revving . That's why it's weird about it only being in top so.....
I'm leaning towards fuelling now ,you can't make power without fuel and air. I've had similar in the past where you could accelerate quickly through 1/2/3 but when you hit 4th it would die. Trouble then was traced to a pump that couldn't keep up with the amount of fuel being used.
I also had this on my 1776 Beetle lump , pulled like a train but on a rolling road it leaned right out in top , fresh pump and regulator fixed that .
I'm thinking that the AFR readings although fine are possibly lower than they should be due to fuel starvation? Who knows ? :( Fuel pump should help with that otherwise I need to check the mixture enrichment set up in the Weber that only kicks in at high velocity.
As I said before, try to find someone with a wideband that you can make use of.
Kev .many years ago i had a 2.0ltr capri with the same problem you've got on the APU ,turned out to be the fuel pump ,changed for a new one plumbed direct to the carb and was told to blank off the return line ,pulled like a train after that .:tup:
Tomorrows job Matt :D Along with changing the timing plate and retiming. I may pop by if I get it done in decent time.
Hi Kev ,thought of something else in the wee small hours ,check the action and length of the fuel pump push rod ,i'll dig out my old work shop manual i'm sure its got the spec's in there.
You are another where the little conundrums just roll around at teh back of your mind then ?:D
I've replaced the timing plate and irt was timed correctly first time :( I've just also advanced it one tooth theh tried it and also retarded one tooth ( 9.47 degrees) and both ways it runs like a sack.
Just changed the fuel pump over and checked the pushrod length 49.90mm if you find the manual to check:tup:. I haven't tried it yet as my back is crucifying me so come to sit down and ease it so I can refit the hood to take it for a trial run.
I seem to have spent forever messing with jets today ,weakening the primary and richening the secondary none which made any improvement. It appears that the high speed enrichment system was also blocked. Cleaned that and STILL no difference.:S
When I crack the throttle hard at standstill I get an earsplitting crack and about 4 inches of fuel reversion ( only from secondary choke ) so my best guess is still cam timing. Guess I'll have to wait until the vernier pulley turns up now.
EDIT . Thinking about it the last time I saw reversion like this was on a twin 40 carbed 1776 Beetle lump, that wouldn't rev cleanly either. That turned out to the exhaust manifold had a plate with holes through it at the end of the manifold and before the silencer. Drilled that out and it revved cleanly . Mmmmm...think if the vernier doesn't sort it then new box next ?
Well, I've pulled of the exhaust system ...all clear :( The only silencer is a straight through oval and although the glass pack is loose in the can the whole system is clear ( rodded it through just to be sure. Fired it up without the exhaust and still flat .
Running out of options here .
Hi Kev, Can't find worshop manual at the mo ,misses tidied up the the loft and can't remember which box she put it in (bless her)!! .I had another thought have you checked the TDC is at TDC had a problem on a sierra once where the crank pulley notch was way out ?
(above not teaching you to suck eggs) could pop around if you want two heads better than one and all that ,had lots of tuned Pinto's in the past might see something ??
Matt, I've just come in to post that very thing ! I'd already checked the TDC on the crank mark but I've just noticed different part numbers on the cam wheels I have here and the one fitted one the engine is a Cortina one ( starts 70-) and the Sierra unit (starts 84-) ,in the garage , has the 'notch' half a tooth different to the Cortina ( so about 4.5 degrees out). I've got to stick the exhaust back on in a minute. Then if I'm up to it I'll swap the pulley over .
4.5 deg's at the cam is quite significant as thats 9 at the crank
Originally Posted by 30psi
4.5 deg's at the cam is quite significant as thats 9 at the crank
Tell me about it !!
The vernier would have sorted it ( still waiting on it to arrive ) but I'd never have found out 'why' , and it woudl have bugged me ( sad I know :lol: ) .
A mate from Essex turned up this afternoon so haven't got it back together yet, so hopefully sorted in the morning .
Originally Posted by kapri
Running out of options here .
Stick one of those swanky 16V heads on it !! (worked for me) :D
Just trying to get it running Chris ;) , plans for the Pinto in the POS though . Well, as I've broken it seems rude not to improve it while it's in bits ;)
It just gets better :roll: Turned out I had a Sierra one on there anyway but timing plates are different as well , I've managed to match the timing plate to the correct cam wheel as I had 2 Sierra camwheels around .
I've also found the camwheels are different even with the same stamped part number ,there is a 20 cast on one and a 25 on another , Cortina one has 14 on it as well .
The timing mark isn't quite right still, probably 3-4 degrees out retarded still but can't fix that until the vernier pulley arrives. Fuel standoff has all but gone though.
Noob question, what do you mean by fuel standoff?
You could still check the cam timing without the vernier to see if it's close to being in time
Fuel standoff ,also known as reversion is when you get a mist of fuel sat above the carb mouth. It's usually caused by pulses in the intake system forcing intake air back up.It's a sign of lots of cam overlap in a performance engine or late valve timing ( or exhaust blocked ) in a milder engine . Isky cams have a good tech answer to the reasons why it happens, I just know it's not a good sign in my engine .
Yup, I could run through setting the exact TDC and cam lift with a dial gauge etc but it's a bit of a workup once installed in the truck .I'd rather only do it once when the vernier wheel gets here. Leaning across the wings and into the bay well and truly screws my back so...
Yeah I understand about your back. Cheers for the info re the fuel reversion
Well I swapped in the Cortina camwheel with approx 4-5 degress less (retarded) ..no difference, it's still just 'flat' . Been looking at the carb to ensure second choke is fuelling through the aux venturi . I'm not conviced that it is but blown it all through and no blockages on that circuit and the high speed enrichment circuit works and that comes from the same emulsion well .
Guess I'll swap in another carb tomorrow so at least it's ruled out :tdown: