Instant Death!!!! Instant Revival!!!!

C

Crestofblue

Registered User
Ok here is the deal....

I have spent the last 10 months of my life putting a 1989 Cougar XR7 engine in my 1994 Mustang. Now that I have finally began to driving it to school and around town its giving me grief. What blows my mind is it runs great, it sounds great, it looks and feels great. However if I try to give it a little gas anymore than a 1/4 of the pedal it instantly dies and instantly revives. It is as if all cylinders stop firing at the same time for a split second and then begin firing again. if I keep my foot in the throttle it bucks. Jerks stops jerks stops and so on. I have some leads and some theories but I cant seem to isolate a solution. Which means I will have to keep buying parts with money i can barely spare until I run across the answer. I would appreciate any insight or advice as to my predicament.

Thanks!!!!
Adam
 
...first check/recheck for vacuum leaks,check plugs and wires to make sure that you don't have a misfire........I had the same problem with my SC and one night I just happened to see a spark plug arcing,found a cracked plug.....
Hopefully it's something as simple as that.........
z
 
check throttle position sensor if all above checks out. you may have to get a data stream type scan tool and actually start looking at sensors and readings while this is happening to narrow it down.
 
Honestly I have always done all the work on my cars myself, so I havent had it tuned, but I really wouldnt even know where to take it to have it tuned. All plugs and wires check out. At one time I had the Bybass valve held open with a vaccum, therefore not allowing boost. While in this condition I obviously had not power but I also didnt have my current problem. So I feel like it must be related to boost. But Im not sure. Ive never heard of this scanning tool to check sensors. Could I rent one somewhere?? How do they work??

Thanks again everyone.

Adam
 
I had this problem on my 94. Exactly the same with the on/off, on/off crap. Check cam sensor. I had a problem where the wiring was rubbed through. I never totally fixed the problem on the car, it just kind of went away. It always happened more when it was wet out too.

Anyways, do a search for bucking and a separate search for surging and you'll get some answers.
 
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I would lean towards a tuning problem....

However, I had an XR-7 that exhibited the same problems as yours....

It ended up being a bad intake gasket....

While the engine is idling, get a section of vacuum tube and put one end in your ear.....

Take the other end and probe around the edges of the intake manifold.....

If there is a leak, you will hear it.....
 
I bought the motor from a guy at a swap meet. Then later I bought an 89 xr7 and pulled the wiring harness so no I am not using a mustang EEC Im using the cougar EEC.

How could a ground problem cause these symptoms?

Thanks again, the help is greatly appreciated!!:)
 
Crestofblue said:
I bought the motor from a guy at a swap meet. Then later I bought an 89 xr7 and pulled the wiring harness so no I am not using a mustang EEC Im using the cougar EEC.

How could a ground problem cause these symptoms?

Thanks again, the help is greatly appreciated!!:)
Click to expand...

A bad ground would basically cause interference with any electrical operation of the motor. So in short, every sensor would be affected in a way.

However, I'm going to say, I don't think it's a vacuum problem, or a gasket. I had the same exact problem. Like I said though, I never really fixed it because it just went away. However, I did fix a number of things that made it happen less. First thing I checked was the Cam sensor and associated wiring, as well as the wiring down to the crank sensor. The crank sensor and wiring was coated in so much crap, but I went ahead and checked it out anyways. I found two wires where the insulation was rubbed through.

I also went around and took every ground I could get access to, took the ground off, stripped all paint and anything else thats on the metal, and put it back on. Make sure to apply a light coat of dialectic grease.

One thing you may want to do, is once it starts doing it, turn the car off. Unplug Cam sensor, and plug it back in. Start the car and see if it does it. I did this when pretty much any sensor that could affect it in such a way to locate the general area of the problem.
 
Crestofblue said:
I bought the motor from a guy at a swap meet. Then later I bought an 89 xr7 and pulled the wiring harness so no I am not using a mustang EEC Im using the cougar EEC.

How could a ground problem cause these symptoms?

Thanks again, the help is greatly appreciated!!:)
Click to expand...

I would use the mustang harness and EEC, its a OBD2 and you can tune it yourself, somewhat. VMP tuning will sell you the tune for the mustang/SC swap. That way you can datalog it and change stuff around. His email is justin@vmptuning.com,

As far as the bucking, check your vacuum routing. The bypass valve is not closing under load.

Justin
 
Surgin said:
I would use the mustang harness and EEC, its a OBD2 and you can tune it yourself, somewhat. VMP tuning will sell you the tune for the mustang/SC swap. That way you can datalog it and change stuff around. His email is justin@vmptuning.com,

As far as the bucking, check your vacuum routing. The bypass valve is not closing under load.

Justin
Click to expand...

An EEC from a 94 mustang is not ODB2 and is still an EEC IV, not V. A basic scanner can be used to get some data from it, but nothing like what a QH could do. A chip will still be needed.

If it is a GURE based setup being used (most likely since that was what the 89/90 XR7's used), then the basics of the tune are in place to support the setup so that will rule the problem out if it is still stock injectors (30#) etc.

It sounds like a car I just recently tuned that had a major boost leak... it was ok at light throttle and idle (not perfect but it ran ok) but give it any gas and it would just fall flat on its face and keel over to boot.

Check for boost leaks as well as vacuum leaks.

Fraser
 
The 94-95 V6 mustang got the OBD2, while the 5.0 got the OBD1, then upgraded in 96.

Justin
 
Doesn't matter, he's not going to be able to use the EEC V without switching timing covers, harmonic balancer, and crank sensor anyway because the EEC V system uses the 36-1 tooth reluctor instead of the 3 vane hall effect that the 89 uses.

If you really want to datalog the car, just get a QH, it's cheaper than an Xcal and pretty well just as useful for datalogging, and 1000x better for tuning (if he's ever so inclined).

The stock tune from the 89 XR7 motor will be better than anything Justin can send him via an Xcal anyway so might as well stick with what he has. As long as the injectors and MAF are stock, it doesn't need tuning.

Sounds like a mechanical problem of some sort anyway. Check all the things already suggested (wiring, grounds, vacuum leaks, etc.).
 
well actually your sitting so uhh :rolleyes:

fturner said:
I stand corrected.

Fraser
Click to expand...



this sounds like my black 90 that i got from new jersey had a problem just as you descibed anything more than ~5 lbs or so of boost and the car would just nose dive and wouldn't recover unless you got off the throttle

this is what was causing my problems

afpr was set at 39psi @ idle with the vac hose still connected :eek:
ignition coil was bad
s/c belt was slipping from tensioner being loose (i remove the belt with my hand)
but mostly... the harmonic balancer failed and would spin inside its housing, the car wouldn't start up with the belt on, would only run with the belt off
 
Listen to XR7DAVE. He knows what he's talking about. He's diagnosed my two major issues (ABS, cam sensor) and all I did was pay attention to his posts.:cool:
 
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