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engine can't be revved up

4K views 54 replies 12 participants last post by  John533i 
#1 · (Edited)
Helping a fellow Alfisti with his 86 Veloce.
He drove it somewhere, parked it and then couldn't get it to restart and hour later.
It had spark, so we started chasing fuel.
Fuel relay, inline fuse, flywheel sensors, battery voltage - all good.
I became convinced it had to be the fuel pressure regulator, so I started to pinch the return line and was able to get it to start and run for a few seconds. I gave him an old spare from a parts car, it got installed and now the car starts and idles, however the engine can't be revved much (maybe to 1500 or so) without getting rough and dying.

I can hear and feel the main pump running, I can hear and feel the in-tank one running, and we pulled it for good measure, and the tank is clean and the stepped hose is intact. Not sure if the sock filter was attached as they tend to fall off as you pull the intank pump. The fuel filter was replaced last year.

I cannot find any vacuum leaks.

At this point, I have a question... can a fuel pressure regulator fail in such a way that it can build up the necessary pressure at idle and not when there is a higher demand for fuel? I tried pinching the return line a bit but it didn't seem to make much difference.

Thanks
 
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#3 ·
Your main pump may be on it's last legs. A fuel pressure gauge isn't very expensive on Amazon; if you install it inline with the cold start injector, you can determine if you have the correct pressure at idle and under throttle, plus if it bleeds off too quickly.
 
#6 ·
I did wonder that myself but kinda ruled it out for now because there was no evident slow deterioration of the exhaust. No funny rattles or noticeable gradual loss of power. Car ran fine, turned it off and sudden problem!

I know there is a vacuum pressure test that can be used to determine possible exhaust blockages but can barely get the engine off idle so might not be possible to test.
 
#8 ·
Common things happen commonly. So check for the usual suspects first.

Is the wire harness connected to the Air Flow Meter? If so, peek inside the connector to be sure the metal connectors have not become displaced. Check the air ducts across the top of the engine. Splits in the accordion section are common - it can be closed while idling but open up when rev'd as the engine rocks on its mounts. Is there enough gas in the tank? If the in-tank pump is weak or not functioning it'll have problems running when the fuel level is below 1/2 full. If possible, add 5 gallons. Did you fill up just before stopping? Could that gas be contaminated? Check inside the vacuum hose that goes to the fuel pressure regulator. There should be no evidence of raw fuel in that hose. If there is the FPR has failed.
 
#10 ·
I did check to make sure the AFM was plugged in but never thought to check the pins. Worth a shot!
Did check the air tubes paying special attention to the accordian and they are good.
Should have mentioned the tank was full, and he did fill up the day before (put about 50 miles on that tank)??
Should have also mentioned that before farting around with the FPR return line, I did pull off the vacuum and no fuel. Is that the only sign of a bad FPR? Can it produce the right pressure at idle and not at higher demand?
 
#11 ·
The FPR is usually quite reliable. The most common failure is the internal diaphragm breaks allowing fuel to get to the (supposed to be) closed vacuum side.

The hose attached to the Cold Start Injector uses a clamp (unlike at the fuel rail). So it is relatively easy to remove the hose there and tee in a gauge. Too much or too little fuel pressure will prevent the engine from running properly.
 

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#14 ·
Yes, cool pic!
Does the fuel pressure gage actually have to be t'd in? Can it just be plugged into the end of the hose when its pulled off the csi, realizing the csi won't be able to spray, so perhaps doing it when the engine is warmed up?
 
#18 ·
Bit of an update.. I think I have proper fuel pressure. I didn't realize but the pressure gauge I just bought only shows up to 10 psi but the needle goes way past that and maxes out to what looks like around 30 psi.. I think the pressure is better than that because the needle shoots so fast.. made a couple videos attached here. I'll buy another pressure gauge to see what it is exactly but I think pressure is good.

Another thing, haven't started her in about a week until today. When I first started her she fired right up and i revved her to around 5000 rpm no problem! Kept revving and she finally died after 20 sec.. I go to start her again and its hard to start and barely stays alive but when she was going after sitting for a while it was like full power.. no idea now.. O2 sensor (was change a year ago)? Bad gas?

Here's some video. All thoughts and ideas appreciated!

https://drive.google.com/file/d/0B1BOtuXCwQ3zRy1oNXd3RzE3Ums/view?usp=drivesdk

https://drive.google.com/file/d/0B1BOtuXCwQ3zay1kSm5NeGR6WUk/view?usp=drivesdk
 
#22 ·
She's alive! So I unplugged the AFM as instructed. She wouldn't start after a lot of attempts. I plugged it back in, tried starting again and she fired up! Took it for a pushing distance drive and she seems fine. Let it cool off for a couple house, tried it again and all good! So strange. Did unplugging the AFM reset something?

I also tried unplugging the AFM while she was running and it died. Plugged it back in and all good. I also unplugged/reconnected the AAV for whatever reason in the middle of all this..

A huge thank you to all for the interest in this thread. Best community ever! :)
 
#23 · (Edited)
#25 ·
Back to square one today! Same symptoms, won't start again. Barely idles. I didn't do a single thing to the car since it was running fine a few days ago. I just tried starting it today and no dice. I unplugged the AFM, connections look good. Scratched them a bit with my nails, no corrosion or anything. Again, any thoughts or suggestions are appreciated!
 
#26 · (Edited)
Make sure the flap inside the AFM moves freely.

There might be wear on the printed circuit board inside the AFM. But check everything else first - double check the flywheel sensors. I've seen a flywheel sensor that tested OK with the ohm meter but when we removed it the end had a dent. We replaced it with good used part and it started right up.
 
#28 ·
We did check to make sure the flap in the AFM moved freely and it did, but I have a spare unit we can try. We did recently replace a dead flywheel sensor with a used one (couple months ago), and although it worked fine initially, could be on its way out. I did have an intermittent issue with one of mine once but it was either fine or dead and wiggling it around did seem to have an effect. Will try that also.

Keep the suggestions coming!
 
#29 ·
CanHam
just backtracking a bit here: you say your fuel pressure tester (in those videos) only goes up to 10psi.....that I find really odd
you certain?

try pinching the FPR return line again and starting her....I mean if it starts with a pinched line I just cannot see the AFM being suspect....more like the FPR
 
#30 ·
Morning, I had this issue and my Timing was out!!! I moved the disty and its been Great since.. Worth a shot as least looking at..

rob s
 
#33 ·
Did a compression test today, here are the results...

From front to back cylinders

Cold engine all plugs in
120
105
120
120

Hot engine plugs in
120
120
125
135

Hot engine plugs out
130
130
135
115

Compression seems good?

Same symptoms, hard to start, takes about 10-15 min, Once shes going she either dies when you give gas or is ok for 5-10 min, can rev to 5000 and then eventually dies.. Very intermittent. Reasons why I was guessing a head gasket failure. As long as I've had her (two years) she leaks a bit of oil or emissions into the coolant. Nothing goes into the oil, it's always been very clean. I do a coolant flush every six months or so and it's clean for a while.

She's been a daily driver for almost two years and she just quit on me last month all of sudden.
 
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